[openwrt/svn-archive/archive.git] / target / linux / generic-2.6 / patches / 000-reinstate-devfs.patch

diff -urN linux-2.6.19.old/arch/cris/arch-v10/kernel/debugport.c linux-2.6.19.dev/arch/cris/arch-v10/kernel/debugport.c
--- linux-2.6.19.old/arch/cris/arch-v10/kernel/debugport.c      2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/cris/arch-v10/kernel/debugport.c      2006-12-14 03:12:59.000000000 +0100
@@ -540,7 +540,7 @@
        dummy_driver.init_termios = tty_std_termios;
        dummy_driver.init_termios.c_cflag =
                B115200 | CS8 | CREAD | HUPCL | CLOCAL; /* is normally B9600 default... */
-       dummy_driver.flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
+       dummy_driver.flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_NO_DEVFS;
 
        dummy_driver.open = dummy_open;
        dummy_driver.close = dummy_close;
diff -urN linux-2.6.19.old/arch/cris/arch-v32/kernel/debugport.c linux-2.6.19.dev/arch/cris/arch-v32/kernel/debugport.c
--- linux-2.6.19.old/arch/cris/arch-v32/kernel/debugport.c      2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/cris/arch-v32/kernel/debugport.c      2006-12-14 03:12:59.000000000 +0100
@@ -352,7 +352,7 @@
        dummy_driver.init_termios = tty_std_termios;
        dummy_driver.init_termios.c_cflag =
                B115200 | CS8 | CREAD | HUPCL | CLOCAL; /* is normally B9600 default... */
-       dummy_driver.flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
+       dummy_driver.flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_NO_DEVFS;
 
        dummy_driver.open = dummy_open;
        dummy_driver.close = dummy_close;
diff -urN linux-2.6.19.old/arch/i386/kernel/microcode.c linux-2.6.19.dev/arch/i386/kernel/microcode.c
--- linux-2.6.19.old/arch/i386/kernel/microcode.c       2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/i386/kernel/microcode.c       2006-12-14 03:12:59.000000000 +0100
@@ -460,6 +460,7 @@
 static struct miscdevice microcode_dev = {
        .minor          = MICROCODE_MINOR,
        .name           = "microcode",
+       .devfs_name     = "cpu/microcode",
        .fops           = &microcode_fops,
 };
 
diff -urN linux-2.6.19.old/arch/ppc/4xx_io/serial_sicc.c linux-2.6.19.dev/arch/ppc/4xx_io/serial_sicc.c
--- linux-2.6.19.old/arch/ppc/4xx_io/serial_sicc.c      2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/ppc/4xx_io/serial_sicc.c      2006-12-14 03:12:59.000000000 +0100
@@ -1757,7 +1757,7 @@
     siccnormal_driver->subtype = SERIAL_TYPE_NORMAL;
     siccnormal_driver->init_termios = tty_std_termios;
     siccnormal_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
-    siccnormal_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
+    siccnormal_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_NO_DEVFS;
     tty_set_operations(siccnormal_driver, &sicc_ops);
 
     if (tty_register_driver(siccnormal_driver))
diff -urN linux-2.6.19.old/arch/sparc64/solaris/socksys.c linux-2.6.19.dev/arch/sparc64/solaris/socksys.c
--- linux-2.6.19.old/arch/sparc64/solaris/socksys.c     2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/sparc64/solaris/socksys.c     2006-12-14 03:12:59.000000000 +0100
@@ -26,6 +26,7 @@
 #include <linux/slab.h>
 #include <linux/syscalls.h>
 #include <linux/in.h>
+#include <linux/devfs_fs_kernel.h>
 
 #include <net/sock.h>
 
@@ -188,6 +189,8 @@
                return ret;
        }
 
+       devfs_mk_cdev(MKDEV(30, 0), S_IFCHR|S_IRUSR|S_IWUSR, "socksys");
+
        file = fcheck(ret);
        /* N.B. Is this valid? Suppose the f_ops are in a module ... */
        socksys_file_ops = *file->f_op;
@@ -202,4 +205,5 @@
 {
        if (unregister_chrdev(30, "socksys"))
                printk ("Couldn't unregister socksys character device\n");
+       devfs_remove ("socksys");
 }
diff -urN linux-2.6.19.old/arch/um/drivers/line.c linux-2.6.19.dev/arch/um/drivers/line.c
--- linux-2.6.19.old/arch/um/drivers/line.c     2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/um/drivers/line.c     2006-12-14 03:12:59.000000000 +0100
@@ -8,6 +8,7 @@
 #include "linux/list.h"
 #include "linux/kd.h"
 #include "linux/interrupt.h"
+#include "linux/devfs_fs_kernel.h"
 #include "asm/uaccess.h"
 #include "chan_kern.h"
 #include "irq_user.h"
@@ -653,6 +654,7 @@
 
        driver->driver_name = line_driver->name;
        driver->name = line_driver->device_name;
+       driver->devfs_name = line_driver->devfs_name;
        driver->major = line_driver->major;
        driver->minor_start = line_driver->minor_start;
        driver->type = line_driver->type;
diff -urN linux-2.6.19.old/arch/um/drivers/ssl.c linux-2.6.19.dev/arch/um/drivers/ssl.c
--- linux-2.6.19.old/arch/um/drivers/ssl.c      2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/um/drivers/ssl.c      2006-12-14 03:12:59.000000000 +0100
@@ -53,6 +53,7 @@
 static struct line_driver driver = {
        .name                   = "UML serial line",
        .device_name            = "ttyS",
+       .devfs_name             = "tts/",
        .major                  = TTY_MAJOR,
        .minor_start            = 64,
        .type                   = TTY_DRIVER_TYPE_SERIAL,
diff -urN linux-2.6.19.old/arch/um/drivers/stdio_console.c linux-2.6.19.dev/arch/um/drivers/stdio_console.c
--- linux-2.6.19.old/arch/um/drivers/stdio_console.c    2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/um/drivers/stdio_console.c    2006-12-14 03:12:59.000000000 +0100
@@ -59,6 +59,7 @@
 static struct line_driver driver = {
        .name                   = "UML console",
        .device_name            = "tty",
+       .devfs_name             = "vc/",
        .major                  = TTY_MAJOR,
        .minor_start            = 0,
        .type                   = TTY_DRIVER_TYPE_CONSOLE,
diff -urN linux-2.6.19.old/arch/um/drivers/ubd_kern.c linux-2.6.19.dev/arch/um/drivers/ubd_kern.c
--- linux-2.6.19.old/arch/um/drivers/ubd_kern.c 2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/um/drivers/ubd_kern.c 2006-12-14 03:12:59.000000000 +0100
@@ -24,6 +24,7 @@
 #include "linux/blkdev.h"
 #include "linux/hdreg.h"
 #include "linux/init.h"
+#include "linux/devfs_fs_kernel.h"
 #include "linux/cdrom.h"
 #include "linux/proc_fs.h"
 #include "linux/ctype.h"
@@ -645,10 +646,14 @@
        disk->first_minor = unit << UBD_SHIFT;
        disk->fops = &ubd_blops;
        set_capacity(disk, size / 512);
-       if(major == MAJOR_NR)
+       if(major == MAJOR_NR){
                sprintf(disk->disk_name, "ubd%c", 'a' + unit);
-       else
+               sprintf(disk->devfs_name, "ubd/disc%d", unit);
+       }
+       else {
                sprintf(disk->disk_name, "ubd_fake%d", unit);
+               sprintf(disk->devfs_name, "ubd_fake/disc%d", unit);
+       }
 
        /* sysfs register (not for ide fake devices) */
        if (major == MAJOR_NR) {
@@ -853,6 +864,7 @@
 {
         int i;
 
+       devfs_mk_dir("ubd");
        if (register_blkdev(MAJOR_NR, "ubd"))
                return -1;
 
@@ -866,6 +878,7 @@
                char name[sizeof("ubd_nnn\0")];
 
                snprintf(name, sizeof(name), "ubd_%d", fake_major);
+               devfs_mk_dir(name);
                if (register_blkdev(fake_major, "ubd"))
                        return -1;
        }
diff -urN linux-2.6.19.old/arch/um/include/line.h linux-2.6.19.dev/arch/um/include/line.h
--- linux-2.6.19.old/arch/um/include/line.h     2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/arch/um/include/line.h     2006-12-14 03:12:59.000000000 +0100
@@ -17,6 +17,7 @@
 struct line_driver {
        char *name;
        char *device_name;
+       char *devfs_name;
        short major;
        short minor_start;
        short type;
diff -urN linux-2.6.19.old/Documentation/Changes linux-2.6.19.dev/Documentation/Changes
--- linux-2.6.19.old/Documentation/Changes      2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/Documentation/Changes      2006-12-14 03:12:59.000000000 +0100
@@ -180,8 +180,8 @@
 --------------------
 
 A driver has been added to allow updating of Intel IA32 microcode,
-accessible as a normal (misc) character device.  If you are not using
-udev you may need to:
+accessible as both a devfs regular file and as a normal (misc)
+character device.  If you are not using devfs you may need to:
 
 mkdir /dev/cpu
 mknod /dev/cpu/microcode c 10 184
@@ -200,9 +200,7 @@
 udev
 ----
 udev is a userspace application for populating /dev dynamically with
-only entries for devices actually present.  udev replaces the basic
-functionality of devfs, while allowing persistant device naming for
-devices.
+only entries for devices actually present. udev replaces devfs.
 
 FUSE
 ----
@@ -232,13 +230,18 @@
 enable it to operate over diverse media layers.  If you use PPP,
 upgrade pppd to at least 2.4.0.
 
-If you are not using udev, you must have the device file /dev/ppp
+If you are not using devfs, you must have the device file /dev/ppp
 which can be made by:
 
 mknod /dev/ppp c 108 0
 
 as root.
 
+If you use devfsd and build ppp support as modules, you will need
+the following in your /etc/devfsd.conf file:
+
+LOOKUP PPP     MODLOAD
+
 Isdn4k-utils
 ------------
 
diff -urN linux-2.6.19.old/Documentation/DocBook/kernel-api.tmpl linux-2.6.19.dev/Documentation/DocBook/kernel-api.tmpl
--- linux-2.6.19.old/Documentation/DocBook/kernel-api.tmpl      2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.19.dev/Documentation/DocBook/kernel-api.tmpl      2006-12-14 03:12:59.000000000 +0100
@@ -84,6 +84,9 @@
 !Ekernel/rcupdate.c
      </sect1>
 
+  <chapter id="devfs">
+     <title>The Device File System</title>
+!Efs/devfs/base.c
   </chapter>
 
   <chapter id="adt">
diff -urN linux-2.6.19.old/Documentation/filesystems/devfs/boot-options linux-2.6.19.dev/Documentation/filesystems/devfs/boot-options
--- linux-2.6.19.old/Documentation/filesystems/devfs/boot-options       1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.19.dev/Documentation/filesystems/devfs/boot-options       2006-12-14 03:12:59.000000000 +0100
@@ -0,0 +1,65 @@
+/* -*- auto-fill -*-                                                         */
+
+               Device File System (devfs) Boot Options
+
+               Richard Gooch <rgooch@atnf.csiro.au>
+
+                             18-AUG-2001
+
+
+When CONFIG_DEVFS_DEBUG is enabled, you can pass several boot options
+to the kernel to debug devfs. The boot options are prefixed by
+"devfs=", and are separated by commas. Spaces are not allowed. The
+syntax looks like this:
+
+devfs=<option1>,<option2>,<option3>
+
+and so on. For example, if you wanted to turn on debugging for module
+load requests and device registration, you would do:
+
+devfs=dmod,dreg
+
+You may prefix "no" to any option. This will invert the option.
+
+
+Debugging Options
+=================
+
+These requires CONFIG_DEVFS_DEBUG to be enabled.
+Note that all debugging options have 'd' as the first character. By
+default all options are off. All debugging output is sent to the
+kernel logs. The debugging options do not take effect until the devfs
+version message appears (just prior to the root filesystem being
+mounted).
+
+These are the options:
+
+dmod           print module load requests to <request_module>
+
+dreg           print device register requests to <devfs_register>
+
+dunreg         print device unregister requests to <devfs_unregister>
+
+dchange                print device change requests to <devfs_set_flags>
+
+dilookup       print inode lookup requests
+
+diget          print VFS inode allocations
+
+diunlink       print inode unlinks
+
+dichange       print inode changes
+
+dimknod                print calls to mknod(2)
+
+dall           some debugging turned on
+
+
+Other Options
+=============
+
+These control the default behaviour of devfs. The options are:
+
+mount          mount devfs onto /dev at boot time
+
+only           disable non-devfs device nodes for devfs-capable drivers
diff -urN linux-2.6.19.old/Documentation/filesystems/devfs/ChangeLog linux-2.6.19.dev/Documentation/filesystems/devfs/ChangeLog
--- linux-2.6.19.old/Documentation/filesystems/devfs/ChangeLog  1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.19.dev/Documentation/filesystems/devfs/ChangeLog  2006-12-14 03:12:59.000000000 +0100
@@ -0,0 +1,1977 @@
+/* -*- auto-fill -*-                                                         */
+===============================================================================
+Changes for patch v1
+
+- creation of devfs
+
+- modified miscellaneous character devices to support devfs
+===============================================================================
+Changes for patch v2
+
+- bug fix with manual inode creation
+===============================================================================
+Changes for patch v3
+
+- bugfixes
+
+- documentation improvements
+
+- created a couple of scripts (one to save&restore a devfs and the
+  other to set up compatibility symlinks)
+
+- devfs support for SCSI discs. New name format is: sd_hHcCiIlL
+===============================================================================
+Changes for patch v4
+
+- bugfix for the directory reading code
+
+- bugfix for compilation with kerneld
+
+- devfs support for generic hard discs
+
+- rationalisation of the various watchdog drivers
+===============================================================================
+Changes for patch v5
+
+- support for mounting directly from entries in the devfs (it doesn't
+  need to be mounted to do this), including the root filesystem.
+  Mounting of swap partitions also works. Hence, now if you set
+  CONFIG_DEVFS_ONLY to 'Y' then you won't be able to access your discs
+  via ordinary device nodes. Naturally, the default is 'N' so that you
+  can still use your old device nodes.  If you want to mount from devfs
+  entries, make sure you use: append = "root=/dev/sd_..." in your
+  lilo.conf. It seems LILO looks for the device number (major&minor)
+  and writes that into the kernel image :-( 
+
+- support for character memory devices (/dev/null, /dev/zero, /dev/full
+  and so on). Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+===============================================================================
+Changes for patch v6
+
+- support for subdirectories
+
+- support for symbolic links (created by devfs_mk_symlink(), no
+  support yet for creation via symlink(2))
+
+- SCSI disc naming now cast in stone, with the format:
+  /dev/sd/c0b1t2u3     controller=0, bus=1, ID=2, LUN=3, whole disc
+  /dev/sd/c0b1t2u3p4   controller=0, bus=1, ID=2, LUN=3, 4th partition
+
+- loop devices now appear in devfs
+
+- tty devices, console, serial ports, etc. now appear in devfs
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- bugs with mounting devfs-only devices now fixed
+===============================================================================
+Changes for patch v7
+
+- SCSI CD-ROMS, tapes and generic devices now appear in devfs
+===============================================================================
+Changes for patch v8
+
+- bugfix with no-rewind SCSI tapes
+
+- RAMDISCs now appear in devfs
+
+- better cleaning up of devfs entries created by various modules
+
+- interface change to <devfs_register>
+===============================================================================
+Changes for patch v9
+
+- the v8 patch was corrupted somehow, which would affect the patch for
+  linux/fs/filesystems.c
+  I've also fixed the v8 patch file on the WWW
+
+- MetaDevices (/dev/md*) should now appear in devfs
+===============================================================================
+Changes for patch v10
+
+- bugfix in meta device support for devfs
+
+- created this ChangeLog file
+
+- added devfs support to the floppy driver
+
+- added support for creating sockets in a devfs
+===============================================================================
+Changes for patch v11
+
+- added DEVFS_FL_HIDE_UNREG flag
+
+- incorporated better patch for ttyname() in libc 5.4.43 from H.J. Lu.
+
+- interface change to <devfs_mk_symlink>
+
+- support for creating symlinks with symlink(2)
+
+- parallel port printer (/dev/lp*) now appears in devfs
+===============================================================================
+Changes for patch v12
+
+- added inode check to <devfs_fill_file> function
+
+- improved devfs support when mounting from devfs
+
+- added call to <<release>> operation when removing swap areas on
+  devfs devices
+
+- increased NR_SUPER to 128 to support large numbers of devfs mounts
+  (for chroot(2) gaols)
+
+- fixed bug in SCSI disc support: was generating incorrect minors if
+  SCSI ID's did not start at 0 and increase by 1
+
+- support symlink traversal when mounting root
+===============================================================================
+Changes for patch v13
+
+- added devfs support to soundcard driver
+  Thanks to Eric Dumas <dumas@linux.eu.org> and
+  C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- added devfs support to the joystick driver
+
+- loop driver now has it's own subdirectory "/dev/loop/"
+
+- created <devfs_get_flags> and <devfs_set_flags> functions
+
+- fix problem with SCSI disc compatibility names (sd{a,b,c,d,e,f})
+  which assumes ID's start at 0 and increase by 1. Also only create
+  devfs entries for SCSI disc partitions which actually exist
+  Show new names in partition check
+  Thanks to Jakub Jelinek <jj@sunsite.ms.mff.cuni.cz>
+===============================================================================
+Changes for patch v14
+
+- bug fix in floppy driver: would not compile without
+  CONFIG_DEVFS_FS='Y'
+  Thanks to Jurgen Botz <jbotz@nova.botz.org>
+
+- bug fix in loop driver
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- do not create devfs entries for printers not configured
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- do not create devfs entries for serial ports not present
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- ensure <tty_register_devfs> is exported from tty_io.c
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- allow unregistering of devfs symlink entries
+
+- fixed bug in SCSI disc naming introduced in last patch version
+===============================================================================
+Changes for patch v15
+
+- ported to kernel 2.1.81
+===============================================================================
+Changes for patch v16
+
+- created <devfs_set_symlink_destination> function
+
+- moved DEVFS_SUPER_MAGIC into header file
+
+- added DEVFS_FL_HIDE flag
+
+- created <devfs_get_maj_min>
+
+- created <devfs_get_handle_from_inode>
+
+- fixed bugs in searching by major&minor
+
+- changed interface to <devfs_unregister>, <devfs_fill_file> and
+  <devfs_find_handle>
+
+- fixed inode times when symlink created with symlink(2)
+
+- change tty driver to do auto-creation of devfs entries
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- fixed bug in genhd.c: whole disc (non-SCSI) was not registered to
+  devfs
+
+- updated libc 5.4.43 patch for ttyname()
+===============================================================================
+Changes for patch v17
+
+- added CONFIG_DEVFS_TTY_COMPAT
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- bugfix in devfs support for drivers/char/lp.c
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- clean up serial driver so that PCMCIA devices unregister correctly
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- fixed bug in genhd.c: whole disc (non-SCSI) was not registered to
+  devfs [was missing in patch v16]
+
+- updated libc 5.4.43 patch for ttyname() [was missing in patch v16]
+
+- all SCSI devices now registered in /dev/sg
+
+- support removal of devfs entries via unlink(2)
+===============================================================================
+Changes for patch v18
+
+- added floppy/?u720 floppy entry
+
+- fixed kerneld support for entries in devfs subdirectories
+
+- incorporated latest patch for ttyname() in libc 5.4.43 from H.J. Lu.
+===============================================================================
+Changes for patch v19
+
+- bug fix when looking up unregistered entries: kerneld was not called
+
+- fixes for kernel 2.1.86 (now requires 2.1.86)
+===============================================================================
+Changes for patch v20
+
+- only create available floppy entries
+  Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
+
+- new IDE naming scheme following SCSI format (i.e. /dev/id/c0b0t0u0p1
+  instead of /dev/hda1)
+  Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
+
+- new XT disc naming scheme following SCSI format (i.e. /dev/xd/c0t0p1
+  instead of /dev/xda1)
+  Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
+
+- new non-standard CD-ROM names (i.e. /dev/sbp/c#t#)
+  Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
+
+- allow symlink traversal when mounting the root filesystem
+
+- Create entries for MD devices at MD init
+  Thanks to Christophe Leroy <christophe.leroy5@capway.com>
+===============================================================================
+Changes for patch v21
+
+- ported to kernel 2.1.91
+===============================================================================
+Changes for patch v22
+
+- SCSI host number patch ("scsihosts=" kernel option)
+  Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
+===============================================================================
+Changes for patch v23
+
+- Fixed persistence bug with device numbers for manually created
+  device files
+
+- Fixed problem with recreating symlinks with different content
+
+- Added CONFIG_DEVFS_MOUNT (mount devfs on /dev at boot time)
+===============================================================================
+Changes for patch v24
+
+- Switched from CONFIG_KERNELD to CONFIG_KMOD: module autoloading
+  should now work again
+
+- Hide entries which are manually unlinked
+
+- Always invalidate devfs dentry cache when registering entries
+
+- Support removal of devfs directories via rmdir(2)
+
+- Ensure directories created by <devfs_mk_dir> are visible
+
+- Default no access for "other" for floppy device
+===============================================================================
+Changes for patch v25
+
+- Updates to CREDITS file and minor IDE numbering change
+  Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
+
+- Invalidate devfs dentry cache when making directories
+
+- Invalidate devfs dentry cache when removing entries
+
+- More informative message if root FS mount fails when devfs
+  configured
+
+- Fixed persistence bug with fifos
+===============================================================================
+Changes for patch v26
+
+- ported to kernel 2.1.97
+
+- Changed serial directory from "/dev/serial" to "/dev/tts" and
+  "/dev/consoles" to "/dev/vc" to be more friendly to new procps
+===============================================================================
+Changes for patch v27
+
+- Added support for IDE4 and IDE5
+  Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
+
+- Documented "scsihosts=" boot parameter
+
+- Print process command when debugging kerneld/kmod
+
+- Added debugging for register/unregister/change operations
+
+- Added "devfs=" boot options
+
+- Hide unregistered entries by default
+===============================================================================
+Changes for patch v28
+
+- No longer lock/unlock superblock in <devfs_put_super> (cope with
+  recent VFS interface change)
+
+- Do not automatically change ownership/protection of /dev/tty
+
+- Drop negative dentries when they are released
+
+- Manage dcache more efficiently
+===============================================================================
+Changes for patch v29
+
+- Added DEVFS_FL_AUTO_DEVNUM flag
+===============================================================================
+Changes for patch v30
+
+- No longer set unnecessary methods
+
+- Ported to kernel 2.1.99-pre3
+===============================================================================
+Changes for patch v31
+
+- Added PID display to <call_kerneld> debugging message
+
+- Added "diread" and "diwrite" options
+
+- Ported to kernel 2.1.102
+
+- Fixed persistence problem with permissions
+===============================================================================
+Changes for patch v32
+
+- Fixed devfs support in drivers/block/md.c
+===============================================================================
+Changes for patch v33
+
+- Support legacy device nodes
+
+- Fixed bug where recreated inodes were hidden
+
+- New IDE naming scheme: everything is under /dev/ide
+===============================================================================
+Changes for patch v34
+
+- Improved debugging in <get_vfs_inode>
+
+- Prevent duplicate calls to <devfs_mk_dir> in SCSI layer
+
+- No longer free old dentries in <devfs_mk_dir>
+
+- Free all dentries for a given entry when deleting inodes
+===============================================================================
+Changes for patch v35
+
+- Ported to kernel 2.1.105 (sound driver changes)
+===============================================================================
+Changes for patch v36
+
+- Fixed sound driver port
+===============================================================================
+Changes for patch v37
+
+- Minor documentation tweaks
+===============================================================================
+Changes for patch v38
+
+- More documentation tweaks
+
+- Fix for sound driver port
+
+- Removed ttyname-patch (grab libc 5.4.44 instead)
+
+- Ported to kernel 2.1.107-pre2 (loop driver fix)
+===============================================================================
+Changes for patch v39
+
+- Ported to kernel 2.1.107 (hd.c hunk broke due to spelling "fixes"). Sigh
+
+- Removed many #ifdef's, replaced with trickery in include/devfs_fs.h
+===============================================================================
+Changes for patch v40
+
+- Fix for sound driver port
+
+- Limit auto-device numbering to majors 128 to 239
+===============================================================================
+Changes for patch v41
+
+- Fixed inode times persistence problem
+===============================================================================
+Changes for patch v42
+
+- Ported to kernel 2.1.108 (drivers/scsi/hosts.c hunk broke)
+===============================================================================
+Changes for patch v43
+
+- Fixed spelling in <devfs_readlink> debug
+
+- Fixed bug in <devfs_setup> parsing "dilookup"
+
+- More #ifdef's removed
+
+- Supported Sparc keyboard (/dev/kbd)
+
+- Supported DSP56001 digital signal processor (/dev/dsp56k)
+
+- Supported Apple Desktop Bus (/dev/adb)
+
+- Supported Coda network file system (/dev/cfs*)
+===============================================================================
+Changes for patch v44
+
+- Fixed devfs inode leak when manually recreating inodes
+
+- Fixed permission persistence problem when recreating inodes
+===============================================================================
+Changes for patch v45
+
+- Ported to kernel 2.1.110
+===============================================================================
+Changes for patch v46
+
+- Ported to kernel 2.1.112-pre1
+
+- Removed harmless "unused variable" compiler warning
+
+- Fixed modes for manually recreated device nodes
+===============================================================================
+Changes for patch v47
+
+- Added NULL devfs inode warning in <devfs_read_inode>
+
+- Force all inode nlink values to 1
+===============================================================================
+Changes for patch v48
+
+- Added "dimknod" option
+
+- Set inode nlink to 0 when freeing dentries
+
+- Added support for virtual console capture devices (/dev/vcs*)
+  Thanks to Dennis Hou <smilax@mindmeld.yi.org>
+
+- Fixed modes for manually recreated symlinks
+===============================================================================
+Changes for patch v49
+
+- Ported to kernel 2.1.113
+===============================================================================
+Changes for patch v50
+
+- Fixed bugs in recreated directories and symlinks
+===============================================================================
+Changes for patch v51
+
+- Improved robustness of rc.devfs script
+  Thanks to Roderich Schupp <rsch@experteam.de>
+
+- Fixed bugs in recreated device nodes
+
+- Fixed bug in currently unused <devfs_get_handle_from_inode>
+
+- Defined new <devfs_handle_t> type
+
+- Improved debugging when getting entries
+
+- Fixed bug where directories could be emptied
+
+- Ported to kernel 2.1.115
+===============================================================================
+Changes for patch v52
+
+- Replaced dummy .epoch inode with .devfsd character device
+
+- Modified rc.devfs to take account of above change
+
+- Removed spurious driver warning messages when CONFIG_DEVFS_FS=n
+
+- Implemented devfsd protocol revision 0
+===============================================================================
+Changes for patch v53
+
+- Ported to kernel 2.1.116 (kmod change broke hunk)
+
+- Updated Documentation/Configure.help
+
+- Test and tty pattern patch for rc.devfs script
+  Thanks to Roderich Schupp <rsch@experteam.de>
+
+- Added soothing message to warning in <devfs_d_iput>
+===============================================================================
+Changes for patch v54
+
+- Ported to kernel 2.1.117
+
+- Fixed default permissions in sound driver
+
+- Added support for frame buffer devices (/dev/fb*)
+===============================================================================
+Changes for patch v55
+
+- Ported to kernel 2.1.119
+
+- Use GCC extensions for structure initialisations
+
+- Implemented async open notification
+
+- Incremented devfsd protocol revision to 1
+===============================================================================
+Changes for patch v56
+
+- Ported to kernel 2.1.120-pre3
+
+- Moved async open notification to end of <devfs_open>
+===============================================================================
+Changes for patch v57
+
+- Ported to kernel 2.1.121
+
+- Prepended "/dev/" to module load request
+
+- Renamed <call_kerneld> to <call_kmod>
+
+- Created sample modules.conf file
+===============================================================================
+Changes for patch v58
+
+- Fixed typo "AYSNC" -> "ASYNC"
+===============================================================================
+Changes for patch v59
+
+- Added open flag for files
+===============================================================================
+Changes for patch v60
+
+- Ported to kernel 2.1.123-pre2
+===============================================================================
+Changes for patch v61
+
+- Set i_blocks=0 and i_blksize=1024 in <devfs_read_inode>
+===============================================================================
+Changes for patch v62
+
+- Ported to kernel 2.1.123
+===============================================================================
+Changes for patch v63
+
+- Ported to kernel 2.1.124-pre2
+===============================================================================
+Changes for patch v64
+
+- Fixed Unix98 pty support
+
+- Increased buffer size in <get_partition_list> to avoid crash and
+  burn
+===============================================================================
+Changes for patch v65
+
+- More Unix98 pty support fixes
+
+- Added test for empty <<name>> in <devfs_find_handle>
+
+- Renamed <generate_path> to <devfs_generate_path> and published
+
+- Created /dev/root symlink
+  Thanks to Roderich Schupp <rsch@ExperTeam.de>
+  with further modifications by me
+===============================================================================
+Changes for patch v66
+
+- Yet more Unix98 pty support fixes (now tested)
+
+- Created <devfs_get_fops>
+
+- Support media change checks when CONFIG_DEVFS_ONLY=y
+
+- Abolished Unix98-style PTY names for old PTY devices
+===============================================================================
+Changes for patch v67
+
+- Added inline declaration for dummy <devfs_generate_path>
+
+- Removed spurious "unable to register... in devfs" messages when
+  CONFIG_DEVFS_FS=n
+
+- Fixed misc. devices when CONFIG_DEVFS_FS=n
+
+- Limit auto-device numbering to majors 144 to 239
+===============================================================================
+Changes for patch v68
+
+- Hide unopened virtual consoles from directory listings
+
+- Added support for video capture devices
+
+- Ported to kernel 2.1.125
+===============================================================================
+Changes for patch v69
+
+- Fix for CONFIG_VT=n
+===============================================================================
+Changes for patch v70
+
+- Added support for non-OSS/Free sound cards
+===============================================================================
+Changes for patch v71
+
+- Ported to kernel 2.1.126-pre2
+===============================================================================
+Changes for patch v72
+
+- #ifdef's for CONFIG_DEVFS_DISABLE_OLD_NAMES removed
+===============================================================================
+Changes for patch v73
+
+- CONFIG_DEVFS_DISABLE_OLD_NAMES replaced with "nocompat" boot option
+
+- CONFIG_DEVFS_BOOT_OPTIONS removed: boot options always available
+===============================================================================
+Changes for patch v74
+
+- Removed CONFIG_DEVFS_MOUNT and "mount" boot option and replaced with
+  "nomount" boot option
+
+- Documentation updates
+
+- Updated sample modules.conf
+===============================================================================
+Changes for patch v75
+
+- Updated sample modules.conf
+
+- Remount devfs after initrd finishes
+
+- Ported to kernel 2.1.127
+
+- Added support for ISDN
+  Thanks to Christophe Leroy <christophe.leroy5@capway.com>
+===============================================================================
+Changes for patch v76
+
+- Updated an email address in ChangeLog
+
+- CONFIG_DEVFS_ONLY replaced with "only" boot option
+===============================================================================
+Changes for patch v77
+
+- Added DEVFS_FL_REMOVABLE flag
+
+- Check for disc change when listing directories with removable media
+  devices
+
+- Use DEVFS_FL_REMOVABLE in sd.c
+
+- Ported to kernel 2.1.128
+===============================================================================
+Changes for patch v78
+
+- Only call <scan_dir_for_removable> on first call to <devfs_readdir>
+
+- Ported to kernel 2.1.129-pre5
+
+- ISDN support improvements
+  Thanks to Christophe Leroy <christophe.leroy5@capway.com>
+===============================================================================
+Changes for patch v79
+
+- Ported to kernel 2.1.130
+
+- Renamed miscdevice "apm" to "apm_bios" to be consistent with
+  devices.txt
+===============================================================================
+Changes for patch v80
+
+- Ported to kernel 2.1.131
+
+- Updated <devfs_rmdir> for VFS change in 2.1.131
+===============================================================================
+Changes for patch v81
+
+- Fixed permissions on /dev/ptmx
+===============================================================================
+Changes for patch v82
+
+- Ported to kernel 2.1.132-pre4
+
+- Changed initial permissions on /dev/pts/*
+
+- Created <devfs_mk_compat>
+
+- Added "symlinks" boot option
+
+- Changed devfs_register_blkdev() back to register_blkdev() for IDE
+
+- Check for partitions on removable media in <devfs_lookup>
+===============================================================================
+Changes for patch v83
+
+- Fixed support for ramdisc when using string-based root FS name
+
+- Ported to kernel 2.2.0-pre1
+===============================================================================
+Changes for patch v84
+
+- Ported to kernel 2.2.0-pre7
+===============================================================================
+Changes for patch v85
+
+- Compile fixes for driver/sound/sound_common.c (non-module) and
+  drivers/isdn/isdn_common.c
+  Thanks to Christophe Leroy <christophe.leroy5@capway.com>
+
+- Added support for registering regular files
+
+- Created <devfs_set_file_size>
+
+- Added /dev/cpu/mtrr as an alternative interface to /proc/mtrr
+
+- Update devfs inodes from entries if not changed through FS
+===============================================================================
+Changes for patch v86
+
+- Ported to kernel 2.2.0-pre9
+===============================================================================
+Changes for patch v87
+
+- Fixed bug when mounting non-devfs devices in a devfs
+===============================================================================
+Changes for patch v88
+
+- Fixed <devfs_fill_file> to only initialise temporary inodes
+
+- Trap for NULL fops in <devfs_register>
+
+- Return -ENODEV in <devfs_fill_file> for non-driver inodes
+
+- Fixed bug when unswapping non-devfs devices in a devfs
+===============================================================================
+Changes for patch v89
+
+- Switched to C data types in include/linux/devfs_fs.h
+
+- Switched from PATH_MAX to DEVFS_PATHLEN
+
+- Updated Documentation/filesystems/devfs/modules.conf to take account
+  of reverse scanning (!) by modprobe
+
+- Ported to kernel 2.2.0
+===============================================================================
+Changes for patch v90
+
+- CONFIG_DEVFS_DISABLE_OLD_TTY_NAMES replaced with "nottycompat" boot
+  option
+
+- CONFIG_DEVFS_TTY_COMPAT removed: existing "symlinks" boot option now
+  controls this. This means you must have libc 5.4.44 or later, or a
+  recent version of libc 6 if you use the "symlinks" option
+===============================================================================
+Changes for patch v91
+
+- Switch from <devfs_mk_symlink> to <devfs_mk_compat> in
+  drivers/char/vc_screen.c to fix problems with Midnight Commander
+===============================================================================
+Changes for patch v92
+
+- Ported to kernel 2.2.2-pre5
+===============================================================================
+Changes for patch v93
+
+- Modified <sd_name> in drivers/scsi/sd.c to cope with devices that
+  don't exist (which happens with new RAID autostart code printk()s)
+===============================================================================
+Changes for patch v94
+
+- Fixed bug in joystick driver: only first joystick was registered
+===============================================================================
+Changes for patch v95
+
+- Fixed another bug in joystick driver
+
+- Fixed <devfsd_read> to not overrun event buffer
+===============================================================================
+Changes for patch v96
+
+- Ported to kernel 2.2.5-2
+
+- Created <devfs_auto_unregister>
+
+- Fixed bugs: compatibility entries were not unregistered for:
+    loop driver
+    floppy driver
+    RAMDISC driver
+    IDE tape driver
+    SCSI CD-ROM driver
+    SCSI HDD driver
+===============================================================================
+Changes for patch v97
+
+- Fixed bugs: compatibility entries were not unregistered for:
+    ALSA sound driver
+    partitions in generic disc driver
+
+- Don't return unregistred entries in <devfs_find_handle>
+
+- Panic in <devfs_unregister> if entry unregistered
+
+- Don't panic in <devfs_auto_unregister> for duplicates
+===============================================================================
+Changes for patch v98
+
+- Don't unregister already unregistered entries in <unregister>
+
+- Register entry in <sd_detect>
+
+- Unregister entry in <sd_detach>
+
+- Changed to <devfs_*register_chrdev> in drivers/char/tty_io.c
+
+- Ported to kernel 2.2.7
+===============================================================================
+Changes for patch v99
+
+- Ported to kernel 2.2.8
+
+- Fixed bug in drivers/scsi/sd.c when >16 SCSI discs
+
+- Disable warning messages when unable to read partition table for
+  removable media
+===============================================================================
+Changes for patch v100
+
+- Ported to kernel 2.3.1-pre5
+
+- Added "oops-on-panic" boot option
+
+- Improved debugging in <devfs_register> and <devfs_unregister>
+
+- Register entry in <sr_detect>
+
+- Unregister entry in <sr_detach>
+
+- Register entry in <sg_detect>
+
+- Unregister entry in <sg_detach>
+
+- Added support for ALSA drivers
+===============================================================================
+Changes for patch v101
+
+- Ported to kernel 2.3.2
+===============================================================================
+Changes for patch v102
+
+- Update serial driver to register PCMCIA entries
+  Thanks to Roch-Alexandre Nomine-Beguin <roch@samarkand.infini.fr>
+
+- Updated an email address in ChangeLog
+
+- Hide virtual console capture entries from directory listings when
+  corresponding console device is not open
+===============================================================================
+Changes for patch v103
+
+- Ported to kernel 2.3.3
+===============================================================================
+Changes for patch v104
+
+- Added documentation for some functions
+
+- Added "doc" target to fs/devfs/Makefile
+
+- Added "v4l" directory for video4linux devices
+
+- Replaced call to <devfs_unregister> in <sd_detach> with call to
+  <devfs_register_partitions>
+
+- Moved registration for sr and sg drivers from detect() to attach()
+  methods
+
+- Register entries in <st_attach> and unregister in <st_detach>
+
+- Work around IDE driver treating CD-ROM as gendisk
+
+- Use <sed> instead of <tr> in rc.devfs
+
+- Updated ToDo list
+
+- Removed "oops-on-panic" boot option: now always Oops
+===============================================================================
+Changes for patch v105
+
+- Unregister SCSI host from <scsi_host_no_list> in <scsi_unregister>
+  Thanks to Zoltán Böszörményi <zboszor@mail.externet.hu>
+
+- Don't save /dev/log in rc.devfs
+
+- Ported to kernel 2.3.4-pre1
+===============================================================================
+Changes for patch v106
+
+- Fixed silly typo in drivers/scsi/st.c
+
+- Improved debugging in <devfs_register>
+===============================================================================
+Changes for patch v107
+
+- Added "diunlink" and "nokmod" boot options
+
+- Removed superfluous warning message in <devfs_d_iput>
+===============================================================================
+Changes for patch v108
+
+- Remove entries when unloading sound module
+===============================================================================
+Changes for patch v109
+
+- Ported to kernel 2.3.6-pre2
+===============================================================================
+Changes for patch v110
+
+- Took account of change to <d_alloc_root>
+===============================================================================
+Changes for patch v111
+
+- Created separate event queue for each mounted devfs
+
+- Removed <devfs_invalidate_dcache>
+
+- Created new ioctl()s for devfsd
+
+- Incremented devfsd protocol revision to 3
+
+- Fixed bug when re-creating directories: contents were lost
+
+- Block access to inodes until devfsd updates permissions
+===============================================================================
+Changes for patch v112
+
+- Modified patch so it applies against 2.3.5 and 2.3.6
+
+- Updated an email address in ChangeLog
+
+- Do not automatically change ownership/protection of /dev/tty<n>
+
+- Updated sample modules.conf
+
+- Switched to sending process uid/gid to devfsd
+
+- Renamed <call_kmod> to <try_modload>
+
+- Added DEVFSD_NOTIFY_LOOKUP event
+
+- Added DEVFSD_NOTIFY_CHANGE event
+
+- Added DEVFSD_NOTIFY_CREATE event
+
+- Incremented devfsd protocol revision to 4
+
+- Moved kernel-specific stuff to include/linux/devfs_fs_kernel.h
+===============================================================================
+Changes for patch v113
+
+- Ported to kernel 2.3.9
+
+- Restricted permissions on some block devices
+===============================================================================
+Changes for patch v114
+
+- Added support for /dev/netlink
+  Thanks to Dennis Hou <smilax@mindmeld.yi.org>
+
+- Return EISDIR rather than EINVAL for read(2) on directories
+
+- Ported to kernel 2.3.10
+===============================================================================
+Changes for patch v115
+
+- Added support for all remaining character devices
+  Thanks to Dennis Hou <smilax@mindmeld.yi.org>
+
+- Cleaned up netlink support
+===============================================================================
+Changes for patch v116
+
+- Added support for /dev/parport%d
+  Thanks to Tim Waugh <tim@cyberelk.demon.co.uk>
+
+- Fixed parallel port ATAPI tape driver
+
+- Fixed Atari SLM laser printer driver
+===============================================================================
+Changes for patch v117
+
+- Added support for COSA card
+  Thanks to Dennis Hou <smilax@mindmeld.yi.org>
+
+- Fixed drivers/char/ppdev.c: missing #include <linux/init.h>
+
+- Fixed drivers/char/ftape/zftape/zftape-init.c
+  Thanks to Vladimir Popov <mashgrad@usa.net>
+===============================================================================
+Changes for patch v118
+
+- Ported to kernel 2.3.15-pre3
+
+- Fixed bug in loop driver
+
+- Unregister /dev/lp%d entries in drivers/char/lp.c
+  Thanks to Maciej W. Rozycki <macro@ds2.pg.gda.pl>
+===============================================================================
+Changes for patch v119
+
+- Ported to kernel 2.3.16
+===============================================================================
+Changes for patch v120
+
+- Fixed bug in drivers/scsi/scsi.c
+
+- Added /dev/ppp
+  Thanks to Dennis Hou <smilax@mindmeld.yi.org>
+
+- Ported to kernel 2.3.17
+===============================================================================
+Changes for patch v121
+
+- Fixed bug in drivers/block/loop.c
+
+- Ported to kernel 2.3.18
+===============================================================================
+Changes for patch v122
+
+- Ported to kernel 2.3.19
+===============================================================================
+Changes for patch v123
+
+- Ported to kernel 2.3.20
+===============================================================================
+Changes for patch v124
+
+- Ported to kernel 2.3.21
+===============================================================================
+Changes for patch v125
+
+- Created <devfs_get_info>, <devfs_set_info>,
+  <devfs_get_first_child> and <devfs_get_next_sibling>
+  Added <<dir>> parameter to <devfs_register>, <devfs_mk_compat>,
+  <devfs_mk_dir> and <devfs_find_handle>
+  Work sponsored by SGI
+
+- Fixed apparent bug in COSA driver
+
+- Re-instated "scsihosts=" boot option
+===============================================================================
+Changes for patch v126
+
+- Always create /dev/pts if CONFIG_UNIX98_PTYS=y
+
+- Fixed call to <devfs_mk_dir> in drivers/block/ide-disk.c
+  Thanks to Dennis Hou <smilax@mindmeld.yi.org>
+
+- Allow multiple unregistrations
+
+- Created /dev/scsi hierarchy
+  Work sponsored by SGI
+===============================================================================
+Changes for patch v127
+
+Work sponsored by SGI
+
+- No longer disable devpts if devfs enabled (caveat emptor)
+
+- Added flags array to struct gendisk and removed code from
+  drivers/scsi/sd.c
+
+- Created /dev/discs hierarchy
+===============================================================================
+Changes for patch v128
+
+Work sponsored by SGI
+
+- Created /dev/cdroms hierarchy
+===============================================================================
+Changes for patch v129
+
+Work sponsored by SGI
+
+- Removed compatibility entries for sound devices
+
+- Removed compatibility entries for printer devices
+
+- Removed compatibility entries for video4linux devices
+
+- Removed compatibility entries for parallel port devices
+
+- Removed compatibility entries for frame buffer devices
+===============================================================================
+Changes for patch v130
+
+Work sponsored by SGI
+
+- Added major and minor number to devfsd protocol
+
+- Incremented devfsd protocol revision to 5
+
+- Removed compatibility entries for SoundBlaster CD-ROMs
+
+- Removed compatibility entries for netlink devices
+
+- Removed compatibility entries for SCSI generic devices
+
+- Removed compatibility entries for SCSI tape devices
+===============================================================================
+Changes for patch v131
+
+Work sponsored by SGI
+
+- Support info pointer for all devfs entry types
+
+- Added <<info>> parameter to <devfs_mk_dir> and <devfs_mk_symlink>
+
+- Removed /dev/st hierarchy
+
+- Removed /dev/sg hierarchy
+
+- Removed compatibility entries for loop devices
+
+- Removed compatibility entries for IDE tape devices
+
+- Removed compatibility entries for SCSI CD-ROMs
+
+- Removed /dev/sr hierarchy
+===============================================================================
+Changes for patch v132
+
+Work sponsored by SGI
+
+- Removed compatibility entries for floppy devices
+
+- Removed compatibility entries for RAMDISCs
+
+- Removed compatibility entries for meta-devices
+
+- Removed compatibility entries for SCSI discs
+
+- Created <devfs_make_root>
+
+- Removed /dev/sd hierarchy
+
+- Support "../" when searching devfs namespace
+
+- Created /dev/ide/host* hierarchy
+
+- Supported IDE hard discs in /dev/ide/host* hierarchy
+
+- Removed compatibility entries for IDE discs
+
+- Removed /dev/ide/hd hierarchy
+
+- Supported IDE CD-ROMs in /dev/ide/host* hierarchy
+
+- Removed compatibility entries for IDE CD-ROMs
+
+- Removed /dev/ide/cd hierarchy
+===============================================================================
+Changes for patch v133
+
+Work sponsored by SGI
+
+- Created <devfs_get_unregister_slave>
+
+- Fixed bug in fs/partitions/check.c when rescanning
+===============================================================================
+Changes for patch v134
+
+Work sponsored by SGI
+
+- Removed /dev/sd, /dev/sr, /dev/st and /dev/sg directories
+
+- Removed /dev/ide/hd directory
+
+- Exported <devfs_get_parent>
+
+- Created <devfs_register_tape> and /dev/tapes hierarchy
+
+- Removed /dev/ide/mt hierarchy
+
+- Removed /dev/ide/fd hierarchy
+
+- Ported to kernel 2.3.25
+===============================================================================
+Changes for patch v135
+
+Work sponsored by SGI
+
+- Removed compatibility entries for virtual console capture devices
+
+- Removed unused <devfs_set_symlink_destination>
+
+- Removed compatibility entries for serial devices
+
+- Removed compatibility entries for console devices
+
+- Do not hide entries from devfsd or children
+
+- Removed DEVFS_FL_TTY_COMPAT flag
+
+- Removed "nottycompat" boot option
+
+- Removed <devfs_mk_compat>
+===============================================================================
+Changes for patch v136
+
+Work sponsored by SGI
+
+- Moved BSD pty devices to /dev/pty
+
+- Added DEVFS_FL_WAIT flag
+===============================================================================
+Changes for patch v137
+
+Work sponsored by SGI
+
+- Really fixed bug in fs/partitions/check.c when rescanning
+
+- Support new "disc" naming scheme in <get_removable_partition>
+
+- Allow NULL fops in <devfs_register>
+
+- Removed redundant name functions in SCSI disc and IDE drivers
+===============================================================================
+Changes for patch v138
+
+Work sponsored by SGI
+
+- Fixed old bugs in drivers/block/paride/pt.c, drivers/char/tpqic02.c,
+  drivers/net/wan/cosa.c and drivers/scsi/scsi.c
+  Thanks to Sergey Kubushin <ksi@ksi-linux.com>
+
+- Fall back to major table if NULL fops given to <devfs_register>
+===============================================================================
+Changes for patch v139
+
+Work sponsored by SGI
+
+- Corrected and moved <get_blkfops> and <get_chrfops> declarations
+  from arch/alpha/kernel/osf_sys.c to include/linux/fs.h
+
+- Removed name function from struct gendisk
+
+- Updated devfs FAQ
+===============================================================================
+Changes for patch v140
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.27
+===============================================================================
+Changes for patch v141
+
+Work sponsored by SGI
+
+- Bug fix in arch/m68k/atari/joystick.c
+
+- Moved ISDN and capi devices to /dev/isdn
+===============================================================================
+Changes for patch v142
+
+Work sponsored by SGI
+
+- Bug fix in drivers/block/ide-probe.c (patch confusion)
+===============================================================================
+Changes for patch v143
+
+Work sponsored by SGI
+
+- Bug fix in drivers/block/blkpg.c:partition_name()
+===============================================================================
+Changes for patch v144
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.29
+
+- Removed calls to <devfs_register> from cdu31a, cm206, mcd and mcdx
+  CD-ROM drivers: generic driver handles this now
+
+- Moved joystick devices to /dev/joysticks
+===============================================================================
+Changes for patch v145
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.30-pre3
+
+- Register whole-disc entry even for invalid partition tables
+
+- Fixed bug in mounting root FS when initrd enabled
+
+- Fixed device entry leak with IDE CD-ROMs
+
+- Fixed compile problem with drivers/isdn/isdn_common.c
+
+- Moved COSA devices to /dev/cosa
+
+- Support fifos when unregistering
+
+- Created <devfs_register_series> and used in many drivers
+
+- Moved Coda devices to /dev/coda
+
+- Moved parallel port IDE tapes to /dev/pt
+
+- Moved parallel port IDE generic devices to /dev/pg
+===============================================================================
+Changes for patch v146
+
+Work sponsored by SGI
+
+- Removed obsolete DEVFS_FL_COMPAT and DEVFS_FL_TOLERANT flags
+
+- Fixed compile problem with fs/coda/psdev.c
+
+- Reinstate change to <devfs_register_blkdev> in
+  drivers/block/ide-probe.c now that fs/isofs/inode.c is fixed
+
+- Switched to <devfs_register_blkdev> in drivers/block/floppy.c,
+  drivers/scsi/sr.c and drivers/block/md.c
+
+- Moved DAC960 devices to /dev/dac960
+===============================================================================
+Changes for patch v147
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.32-pre4
+===============================================================================
+Changes for patch v148
+
+Work sponsored by SGI
+
+- Removed kmod support: use devfsd instead
+
+- Moved miscellaneous character devices to /dev/misc
+===============================================================================
+Changes for patch v149
+
+Work sponsored by SGI
+
+- Ensure include/linux/joystick.h is OK for user-space
+
+- Improved debugging in <get_vfs_inode>
+
+- Ensure dentries created by devfsd will be cleaned up
+===============================================================================
+Changes for patch v150
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.34
+===============================================================================
+Changes for patch v151
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.35-pre1
+
+- Created <devfs_get_name>
+===============================================================================
+Changes for patch v152
+
+Work sponsored by SGI
+
+- Updated sample modules.conf
+
+- Ported to kernel 2.3.36-pre1
+===============================================================================
+Changes for patch v153
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.42
+
+- Removed <devfs_fill_file>
+===============================================================================
+Changes for patch v154
+
+Work sponsored by SGI
+
+- Took account of device number changes for /dev/fb*
+===============================================================================
+Changes for patch v155
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.43-pre8
+
+- Moved /dev/tty0 to /dev/vc/0
+
+- Moved sequence number formatting from <_tty_make_name> to drivers
+===============================================================================
+Changes for patch v156
+
+Work sponsored by SGI
+
+- Fixed breakage in drivers/scsi/sd.c due to recent SCSI changes
+===============================================================================
+Changes for patch v157
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.45
+===============================================================================
+Changes for patch v158
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.46-pre2
+===============================================================================
+Changes for patch v159
+
+Work sponsored by SGI
+
+- Fixed drivers/block/md.c
+  Thanks to Mike Galbraith <mikeg@weiden.de>
+
+- Documentation fixes
+
+- Moved device registration from <lp_init> to <lp_register>
+  Thanks to Tim Waugh <twaugh@redhat.com>
+===============================================================================
+Changes for patch v160
+
+Work sponsored by SGI
+
+- Fixed drivers/char/joystick/joystick.c
+  Thanks to Vojtech Pavlik <vojtech@suse.cz>
+
+- Documentation updates
+
+- Fixed arch/i386/kernel/mtrr.c if procfs and devfs not enabled
+
+- Fixed drivers/char/stallion.c
+===============================================================================
+Changes for patch v161
+
+Work sponsored by SGI
+
+- Remove /dev/ide when ide-mod is unloaded
+
+- Fixed bug in drivers/block/ide-probe.c when secondary but no primary
+
+- Added DEVFS_FL_NO_PERSISTENCE flag
+
+- Used new DEVFS_FL_NO_PERSISTENCE flag for Unix98 pty slaves
+
+- Removed unnecessary call to <update_devfs_inode_from_entry> in
+  <devfs_readdir>
+
+- Only set auto-ownership for /dev/pty/s*
+===============================================================================
+Changes for patch v162
+
+Work sponsored by SGI
+
+- Set inode->i_size to correct size for symlinks
+  Thanks to Jeremy Fitzhardinge <jeremy@goop.org>
+
+- Only give lookup() method to directories to comply with new VFS
+  assumptions
+
+- Remove unnecessary tests in symlink methods
+
+- Don't kill existing block ops in <devfs_read_inode>
+
+- Restore auto-ownership for /dev/pty/m*
+===============================================================================
+Changes for patch v163
+
+Work sponsored by SGI
+
+- Don't create missing directories in <devfs_find_handle>
+
+- Removed Documentation/filesystems/devfs/mk-devlinks
+
+- Updated Documentation/filesystems/devfs/README
+===============================================================================
+Changes for patch v164
+
+Work sponsored by SGI
+
+- Fixed CONFIG_DEVFS breakage in drivers/char/serial.c introduced in
+  linux-2.3.99-pre6-7
+===============================================================================
+Changes for patch v165
+
+Work sponsored by SGI
+
+- Ported to kernel 2.3.99-pre6
+===============================================================================
+Changes for patch v166
+
+Work sponsored by SGI
+
+- Added CONFIG_DEVFS_MOUNT
+===============================================================================
+Changes for patch v167
+
+Work sponsored by SGI
+
+- Updated Documentation/filesystems/devfs/README
+
+- Updated sample modules.conf
+===============================================================================
+Changes for patch v168
+
+Work sponsored by SGI
+
+- Disabled multi-mount capability (use VFS bindings instead)
+
+- Updated README from master HTML file
+===============================================================================
+Changes for patch v169
+
+Work sponsored by SGI
+
+- Removed multi-mount code
+
+- Removed compatibility macros: VFS has changed too much
+===============================================================================
+Changes for patch v170
+
+Work sponsored by SGI
+
+- Updated README from master HTML file
+
+- Merged devfs inode into devfs entry
+===============================================================================
+Changes for patch v171
+
+Work sponsored by SGI
+
+- Updated sample modules.conf
+
+- Removed dead code in <devfs_register> which used to call
+  <free_dentries>
+
+- Ported to kernel 2.4.0-test2-pre3
+===============================================================================
+Changes for patch v172
+
+Work sponsored by SGI
+
+- Changed interface to <devfs_register>
+
+- Changed interface to <devfs_register_series>
+===============================================================================
+Changes for patch v173
+
+Work sponsored by SGI
+
+- Simplified interface to <devfs_mk_symlink>
+
+- Simplified interface to <devfs_mk_dir>
+
+- Simplified interface to <devfs_find_handle>
+===============================================================================
+Changes for patch v174
+
+Work sponsored by SGI
+
+- Updated README from master HTML file
+===============================================================================
+Changes for patch v175
+
+Work sponsored by SGI
+
+- DocBook update for fs/devfs/base.c
+  Thanks to Tim Waugh <twaugh@redhat.com>
+
+- Removed stale fs/tunnel.c (was never used or completed)
+===============================================================================
+Changes for patch v176
+
+Work sponsored by SGI
+
+- Updated ToDo list
+
+- Removed sample modules.conf: now distributed with devfsd
+
+- Updated README from master HTML file
+
+- Ported to kernel 2.4.0-test3-pre4 (which had devfs-patch-v174)
+===============================================================================
+Changes for patch v177
+
+- Updated README from master HTML file
+
+- Documentation cleanups
+
+- Ensure <devfs_generate_path> terminates string for root entry
+  Thanks to Tim Jansen <tim@tjansen.de>
+
+- Exported <devfs_get_name> to modules
+
+- Make <devfs_mk_symlink> send events to devfsd
+
+- Cleaned up option processing in <devfs_setup>
+
+- Fixed bugs in handling symlinks: could leak or cause Oops
+
+- Cleaned up directory handling by separating fops
+  Thanks to Alexander Viro <viro@parcelfarce.linux.theplanet.co.uk>
+===============================================================================
+Changes for patch v178
+
+- Fixed handling of inverted options in <devfs_setup>
+===============================================================================
+Changes for patch v179
+
+- Adjusted <try_modload> to account for <devfs_generate_path> fix
+===============================================================================
+Changes for patch v180
+
+- Fixed !CONFIG_DEVFS_FS stub declaration of <devfs_get_info>
+===============================================================================
+Changes for patch v181
+
+- Answered question posed by Al Viro and removed his comments from <devfs_open>
+
+- Moved setting of registered flag after other fields are changed
+
+- Fixed race between <devfsd_close> and <devfsd_notify_one>
+
+- Global VFS changes added bogus BKL to devfsd_close(): removed
+
+- Widened locking in <devfs_readlink> and <devfs_follow_link>
+
+- Replaced <devfsd_read> stack usage with <devfsd_ioctl> kmalloc
+
+- Simplified locking in <devfsd_ioctl> and fixed memory leak
+===============================================================================
+Changes for patch v182
+
+- Created <devfs_*alloc_major> and <devfs_*alloc_devnum>
+
+- Removed broken devnum allocation and use <devfs_alloc_devnum>
+
+- Fixed old devnum leak by calling new <devfs_dealloc_devnum>
+
+- Created <devfs_*alloc_unique_number>
+
+- Fixed number leak for /dev/cdroms/cdrom%d
+
+- Fixed number leak for /dev/discs/disc%d
+===============================================================================
+Changes for patch v183
+
+- Fixed bug in <devfs_setup> which could hang boot process
+===============================================================================
+Changes for patch v184
+
+- Documentation typo fix for fs/devfs/util.c
+
+- Fixed drivers/char/stallion.c for devfs
+
+- Added DEVFSD_NOTIFY_DELETE event
+
+- Updated README from master HTML file
+
+- Removed #include <asm/segment.h> from fs/devfs/base.c
+===============================================================================
+Changes for patch v185
+
+- Made <block_semaphore> and <char_semaphore> in fs/devfs/util.c
+  private
+
+- Fixed inode table races by removing it and using inode->u.generic_ip
+  instead
+
+- Moved <devfs_read_inode> into <get_vfs_inode>
+
+- Moved <devfs_write_inode> into <devfs_notify_change>
+===============================================================================
+Changes for patch v186
+
+- Fixed race in <devfs_do_symlink> for uni-processor
+
+- Updated README from master HTML file
+===============================================================================
+Changes for patch v187
+
+- Fixed drivers/char/stallion.c for devfs
+
+- Fixed drivers/char/rocket.c for devfs
+
+- Fixed bug in <devfs_alloc_unique_number>: limited to 128 numbers
+===============================================================================
+Changes for patch v188
+
+- Updated major masks in fs/devfs/util.c up to Linus' "no new majors"
+  proclamation. Block: were 126 now 122 free, char: were 26 now 19 free
+
+- Updated README from master HTML file
+
+- Removed remnant of multi-mount support in <devfs_mknod>
+
+- Removed unused DEVFS_FL_SHOW_UNREG flag
+===============================================================================
+Changes for patch v189
+
+- Removed nlink field from struct devfs_inode
+
+- Removed auto-ownership for /dev/pty/* (BSD ptys) and used
+  DEVFS_FL_CURRENT_OWNER|DEVFS_FL_NO_PERSISTENCE for /dev/pty/s* (just
+  like Unix98 pty slaves) and made /dev/pty/m* rw-rw-rw- access
+===============================================================================
+Changes for patch v190
+
+- Updated README from master HTML file
+
+- Replaced BKL with global rwsem to protect symlink data (quick and
+  dirty hack)
+===============================================================================
+Changes for patch v191
+
+- Replaced global rwsem for symlink with per-link refcount
+===============================================================================
+Changes for patch v192
+
+- Removed unnecessary #ifdef CONFIG_DEVFS_FS from arch/i386/kernel/mtrr.c
+
+- Ported to kernel 2.4.10-pre11
+
+- Set inode->i_mapping->a_ops for block nodes in <get_vfs_inode>
+===============================================================================
+Changes for patch v193
+
+- Went back to global rwsem for symlinks (refcount scheme no good)
+===============================================================================
+Changes for patch v194
+
+- Fixed overrun in <devfs_link> by removing function (not needed)
+
+- Updated README from master HTML file
+===============================================================================
+Changes for patch v195
+
+- Fixed buffer underrun in <try_modload>
+
+- Moved down_read() from <search_for_entry_in_dir> to <find_entry>
+===============================================================================
+Changes for patch v196
+
+- Fixed race in <devfsd_ioctl> when setting event mask
+  Thanks to Kari Hurtta <hurtta@leija.mh.fmi.fi>
+
+- Avoid deadlock in <devfs_follow_link> by using temporary buffer
+===============================================================================
+Changes for patch v197
+
+- First release of new locking code for devfs core (v1.0)
+
+- Fixed bug in drivers/cdrom/cdrom.c
+===============================================================================
+Changes for patch v198
+
+- Discard temporary buffer, now use "%s" for dentry names
+
+- Don't generate path in <try_modload>: use fake entry instead
+
+- Use "existing" directory in <_devfs_make_parent_for_leaf>
+
+- Use slab cache rather than fixed buffer for devfsd events
+===============================================================================
+Changes for patch v199
+
+- Removed obsolete usage of DEVFS_FL_NO_PERSISTENCE
+
+- Send DEVFSD_NOTIFY_REGISTERED events in <devfs_mk_dir>
+
+- Fixed locking bug in <devfs_d_revalidate_wait> due to typo
+
+- Do not send CREATE, CHANGE, ASYNC_OPEN or DELETE events from devfsd
+  or children
+===============================================================================
+Changes for patch v200
+
+- Ported to kernel 2.5.1-pre2
+===============================================================================
+Changes for patch v201
+
+- Fixed bug in <devfsd_read>: was dereferencing freed pointer
+===============================================================================
+Changes for patch v202
+
+- Fixed bug in <devfsd_close>: was dereferencing freed pointer
+
+- Added process group check for devfsd privileges
+===============================================================================
+Changes for patch v203
+
+- Use SLAB_ATOMIC in <devfsd_notify_de> from <devfs_d_delete>
+===============================================================================
+Changes for patch v204
+
+- Removed long obsolete rc.devfs
+
+- Return old entry in <devfs_mk_dir> for 2.4.x kernels
+
+- Updated README from master HTML file
+
+- Increment refcount on module in <check_disc_changed>
+
+- Created <devfs_get_handle> and exported <devfs_put>
+
+- Increment refcount on module in <devfs_get_ops>
+
+- Created <devfs_put_ops> and used where needed to fix races
+
+- Added clarifying comments in response to preliminary EMC code review
+
+- Added poisoning to <devfs_put>
+
+- Improved debugging messages
+
+- Fixed unregister bugs in drivers/md/lvm-fs.c
+===============================================================================
+Changes for patch v205
+
+- Corrected (made useful) debugging message in <unregister>
+
+- Moved <kmem_cache_create> in <mount_devfs_fs> to <init_devfs_fs>
+
+- Fixed drivers/md/lvm-fs.c to create "lvm" entry
+
+- Added magic number to guard against scribbling drivers
+
+- Only return old entry in <devfs_mk_dir> if a directory
+
+- Defined macros for error and debug messages
+
+- Updated README from master HTML file
+===============================================================================
+Changes for patch v206
+
+- Added support for multiple Compaq cpqarray controllers
+
+- Fixed (rare, old) race in <devfs_lookup>
+===============================================================================
+Changes for patch v207
+
+- Fixed deadlock bug in <devfs_d_revalidate_wait>
+
+- Tag VFS deletable in <devfs_mk_symlink> if handle ignored
+
+- Updated README from master HTML file
+===============================================================================
+Changes for patch v208
+
+- Added KERN_* to remaining messages
+
+- Cleaned up declaration of <stat_read>
+
+- Updated README from master HTML file
+===============================================================================
+Changes for patch v209
+
+- Updated README from master HTML file
+
+- Removed silently introduced calls to lock_kernel() and
+  unlock_kernel() due to recent VFS locking changes. BKL isn't
+  required in devfs 
+
+- Changed <devfs_rmdir> to allow later additions if not yet empty
+
+- Added calls to <devfs_register_partitions> in drivers/block/blkpc.c
+  <add_partition> and <del_partition>
+
+- Fixed bug in <devfs_alloc_unique_number>: was clearing beyond
+  bitfield
+
+- Fixed bitfield data type for <devfs_*alloc_devnum>
+
+- Made major bitfield type and initialiser 64 bit safe
+===============================================================================
+Changes for patch v210
+
+- Updated fs/devfs/util.c to fix shift warning on 64 bit machines
+  Thanks to Anton Blanchard <anton@samba.org>
+
+- Updated README from master HTML file
+===============================================================================
+Changes for patch v211
+
+- Do not put miscellaneous character devices in /dev/misc if they
+  specify their own directory (i.e. contain a '/' character)
+
+- Copied macro for error messages from fs/devfs/base.c to
+  fs/devfs/util.c and made use of this macro
+
+- Removed 2.4.x compatibility code from fs/devfs/base.c
+===============================================================================
+Changes for patch v212
+
+- Added BKL to <devfs_open> because drivers still need it
+===============================================================================
+Changes for patch v213
+
+- Protected <scan_dir_for_removable> and <get_removable_partition>
+  from changing directory contents
+===============================================================================
+Changes for patch v214
+
+- Switched to ISO C structure field initialisers
+
+- Switch to set_current_state() and move before add_wait_queue()
+
+- Updated README from master HTML file
+
+- Fixed devfs entry leak in <devfs_readdir> when *readdir fails
+===============================================================================
+Changes for patch v215
+
+- Created <devfs_find_and_unregister>
+
+- Switched many functions from <devfs_find_handle> to
+  <devfs_find_and_unregister>
+
+- Switched many functions from <devfs_find_handle> to <devfs_get_handle>
+===============================================================================
+Changes for patch v216
+
+- Switched arch/ia64/sn/io/hcl.c from <devfs_find_handle> to
+  <devfs_get_handle>
+
+- Removed deprecated <devfs_find_handle>
+===============================================================================
+Changes for patch v217
+
+- Exported <devfs_find_and_unregister> and <devfs_only> to modules
+
+- Updated README from master HTML file
+
+- Fixed module unload race in <devfs_open>
+===============================================================================
+Changes for patch v218
+
+- Removed DEVFS_FL_AUTO_OWNER flag
+
+- Switched lingering structure field initialiser to ISO C
+
+- Added locking when setting/clearing flags
+
+- Documentation fix in fs/devfs/util.c
diff -urN linux-2.6.19.old/Documentation/filesystems/devfs/README linux-2.6.19.dev/Documentation/filesystems/devfs/README
--- linux-2.6.19.old/Documentation/filesystems/devfs/README     1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.19.dev/Documentation/filesystems/devfs/README     2006-12-14 03:12:59.000000000 +0100
@@ -0,0 +1,1959 @@
+Devfs (Device File System) FAQ
+
+
+Linux Devfs (Device File System) FAQ
+Richard Gooch
+20-AUG-2002
+
+
+Document languages:
+
+
+
+
+
+
+
+-----------------------------------------------------------------------------
+
+NOTE: the master copy of this document is available online at:
+
+http://www.atnf.csiro.au/~rgooch/linux/docs/devfs.html
+and looks much better than the text version distributed with the
+kernel sources. A mirror site is available at:
+
+http://www.ras.ucalgary.ca/~rgooch/linux/docs/devfs.html
+
+There is also an optional daemon that may be used with devfs. You can
+find out more about it at:
+
+http://www.atnf.csiro.au/~rgooch/linux/
+
+A mailing list is available which you may subscribe to. Send
+email
+to majordomo@oss.sgi.com with the following line in the
+body of the message:
+subscribe devfs
+To unsubscribe, send the message body:
+unsubscribe devfs
+instead. The list is archived at
+
+http://oss.sgi.com/projects/devfs/archive/.
+
+-----------------------------------------------------------------------------
+
+Contents
+
+
+What is it?
+
+Why do it?
+
+Who else does it?
+
+How it works
+
+Operational issues (essential reading)
+
+Instructions for the impatient
+Permissions persistence across reboots
+Dealing with drivers without devfs support
+All the way with Devfs
+Other Issues
+Kernel Naming Scheme
+Devfsd Naming Scheme
+Old Compatibility Names
+SCSI Host Probing Issues
+
+
+
+Device drivers currently ported
+
+Allocation of Device Numbers
+
+Questions and Answers
+
+Making things work
+Alternatives to devfs
+What I don't like about devfs
+How to report bugs
+Strange kernel messages
+Compilation problems with devfsd
+
+
+Other resources
+
+Translations of this document
+
+
+-----------------------------------------------------------------------------
+
+
+What is it?
+
+Devfs is an alternative to "real" character and block special devices
+on your root filesystem. Kernel device drivers can register devices by
+name rather than major and minor numbers. These devices will appear in
+devfs automatically, with whatever default ownership and
+protection the driver specified. A daemon (devfsd) can be used to
+override these defaults. Devfs has been in the kernel since 2.3.46.
+
+NOTE that devfs is entirely optional. If you prefer the old
+disc-based device nodes, then simply leave CONFIG_DEVFS_FS=n (the
+default). In this case, nothing will change.  ALSO NOTE that if you do
+enable devfs, the defaults are such that full compatibility is
+maintained with the old devices names.
+
+There are two aspects to devfs: one is the underlying device
+namespace, which is a namespace just like any mounted filesystem. The
+other aspect is the filesystem code which provides a view of the
+device namespace. The reason I make a distinction is because devfs
+can be mounted many times, with each mount showing the same device
+namespace. Changes made are global to all mounted devfs filesystems.
+Also, because the devfs namespace exists without any devfs mounts, you
+can easily mount the root filesystem by referring to an entry in the
+devfs namespace.
+
+
+The cost of devfs is a small increase in kernel code size and memory
+usage. About 7 pages of code (some of that in __init sections) and 72
+bytes for each entry in the namespace. A modest system has only a
+couple of hundred device entries, so this costs a few more
+pages. Compare this with the suggestion to put /dev on a <a
+href="#why-faq-ramdisc">ramdisc.
+
+On a typical machine, the cost is under 0.2 percent. On a modest
+system with 64 MBytes of RAM, the cost is under 0.1 percent.  The
+accusations of "bloatware" levelled at devfs are not justified.
+
+-----------------------------------------------------------------------------
+
+
+Why do it?
+
+There are several problems that devfs addresses. Some of these
+problems are more serious than others (depending on your point of
+view), and some can be solved without devfs. However, the totality of
+these problems really calls out for devfs.
+
+The choice is a patchwork of inefficient user space solutions, which
+are complex and likely to be fragile, or to use a simple and efficient
+devfs which is robust.
+
+There have been many counter-proposals to devfs, all seeking to
+provide some of the benefits without actually implementing devfs. So
+far there has been an absence of code and no proposed alternative has
+been able to provide all the features that devfs does. Further,
+alternative proposals require far more complexity in user-space (and
+still deliver less functionality than devfs). Some people have the
+mantra of reducing "kernel bloat", but don't consider the effects on
+user-space.
+
+A good solution limits the total complexity of kernel-space and
+user-space.
+
+
+Major&minor allocation
+
+The existing scheme requires the allocation of major and minor device
+numbers for each and every device. This means that a central
+co-ordinating authority is required to issue these device numbers
+(unless you're developing a "private" device driver), in order to
+preserve uniqueness. Devfs shifts the burden to a namespace. This may
+not seem like a huge benefit, but actually it is. Since driver authors
+will naturally choose a device name which reflects the functionality
+of the device, there is far less potential for namespace conflict.
+Solving this requires a kernel change.
+
+/dev management
+
+Because you currently access devices through device nodes, these must
+be created by the system administrator. For standard devices you can
+usually find a MAKEDEV programme which creates all these (hundreds!)
+of nodes. This means that changes in the kernel must be reflected by
+changes in the MAKEDEV programme, or else the system administrator
+creates device nodes by hand.
+
+The basic problem is that there are two separate databases of
+major and minor numbers. One is in the kernel and one is in /dev (or
+in a MAKEDEV programme, if you want to look at it that way). This is
+duplication of information, which is not good practice.
+Solving this requires a kernel change.
+
+/dev growth
+
+A typical /dev has over 1200 nodes! Most of these devices simply don't
+exist because the hardware is not available. A huge /dev increases the
+time to access devices (I'm just referring to the dentry lookup times
+and the time taken to read inodes off disc: the next subsection shows
+some more horrors).
+
+An example of how big /dev can grow is if we consider SCSI devices:
+
+host           6  bits  (say up to 64 hosts on a really big machine)
+channel        4  bits  (say up to 16 SCSI buses per host)
+id             4  bits
+lun            3  bits
+partition      6  bits
+TOTAL          23 bits
+
+
+This requires 8 Mega (1024*1024) inodes if we want to store all
+possible device nodes. Even if we scrap everything but id,partition
+and assume a single host adapter with a single SCSI bus and only one
+logical unit per SCSI target (id), that's still 10 bits or 1024
+inodes. Each VFS inode takes around 256 bytes (kernel 2.1.78), so
+that's 256 kBytes of inode storage on disc (assuming real inodes take
+a similar amount of space as VFS inodes). This is actually not so bad,
+because disc is cheap these days. Embedded systems would care about
+256 kBytes of /dev inodes, but you could argue that embedded systems
+would have hand-tuned /dev directories. I've had to do just that on my
+embedded systems, but I would rather just leave it to devfs.
+
+Another issue is the time taken to lookup an inode when first
+referenced. Not only does this take time in scanning through a list in
+memory, but also the seek times to read the inodes off disc.
+This could be solved in user-space using a clever programme which
+scanned the kernel logs and deleted /dev entries which are not
+available and created them when they were available. This programme
+would need to be run every time a new module was loaded, which would
+slow things down a lot.
+
+There is an existing programme called scsidev which will automatically
+create device nodes for SCSI devices. It can do this by scanning files
+in /proc/scsi. Unfortunately, to extend this idea to other device
+nodes would require significant modifications to existing drivers (so
+they too would provide information in /proc). This is a non-trivial
+change (I should know: devfs has had to do something similar). Once
+you go to this much effort, you may as well use devfs itself (which
+also provides this information).  Furthermore, such a system would
+likely be implemented in an ad-hoc fashion, as different drivers will
+provide their information in different ways.
+
+Devfs is much cleaner, because it (naturally) has a uniform mechanism
+to provide this information: the device nodes themselves!
+
+
+Node to driver file_operations translation
+
+There is an important difference between the way disc-based character
+and block nodes and devfs entries make the connection between an entry
+in /dev and the actual device driver.
+
+With the current 8 bit major and minor numbers the connection between
+disc-based c&b nodes and per-major drivers is done through a
+fixed-length table of 128 entries. The various filesystem types set
+the inode operations for c&b nodes to {chr,blk}dev_inode_operations,
+so when a device is opened a few quick levels of indirection bring us
+to the driver file_operations.
+
+For miscellaneous character devices a second step is required: there
+is a scan for the driver entry with the same minor number as the file
+that was opened, and the appropriate minor open method is called. This
+scanning is done *every time* you open a device node. Potentially, you
+may be searching through dozens of misc. entries before you find your
+open method. While not an enormous performance overhead, this does
+seem pointless.
+
+Linux *must* move beyond the 8 bit major and minor barrier,
+somehow. If we simply increase each to 16 bits, then the indexing
+scheme used for major driver lookup becomes untenable, because the
+major tables (one each for character and block devices) would need to
+be 64 k entries long (512 kBytes on x86, 1 MByte for 64 bit
+systems). So we would have to use a scheme like that used for
+miscellaneous character devices, which means the search time goes up
+linearly with the average number of major device drivers on your
+system. Not all "devices" are hardware, some are higher-level drivers
+like KGI, so you can get more "devices" without adding hardware
+You can improve this by creating an ordered (balanced:-)
+binary tree, in which case your search time becomes log(N).
+Alternatively, you can use hashing to speed up the search.
+But why do that search at all if you don't have to? Once again, it
+seems pointless.
+
+Note that devfs doesn't use the major&minor system. For devfs
+entries, the connection is done when you lookup the /dev entry. When
+devfs_register() is called, an internal table is appended which has
+the entry name and the file_operations. If the dentry cache doesn't
+have the /dev entry already, this internal table is scanned to get the
+file_operations, and an inode is created. If the dentry cache already
+has the entry, there is *no lookup time* (other than the dentry scan
+itself, but we can't avoid that anyway, and besides Linux dentries
+cream other OS's which don't have them:-). Furthermore, the number of
+node entries in a devfs is only the number of available device
+entries, not the number of *conceivable* entries. Even if you remove
+unnecessary entries in a disc-based /dev, the number of conceivable
+entries remains the same: you just limit yourself in order to save
+space.
+
+Devfs provides a fast connection between a VFS node and the device
+driver, in a scalable way.
+
+/dev as a system administration tool
+
+Right now /dev contains a list of conceivable devices, most of which I
+don't have. Devfs only shows those devices available on my
+system. This means that listing /dev is a handy way of checking what
+devices are available.
+
+Major&minor size
+
+Existing major and minor numbers are limited to 8 bits each. This is
+now a limiting factor for some drivers, particularly the SCSI disc
+driver, which consumes a single major number. Only 16 discs are
+supported, and each disc may have only 15 partitions. Maybe this isn't
+a problem for you, but some of us are building huge Linux systems with
+disc arrays. With devfs an arbitrary pointer can be associated with
+each device entry, which can be used to give an effective 32 bit
+device identifier (i.e. that's like having a 32 bit minor
+number). Since this is private to the kernel, there are no C library
+compatibility issues which you would have with increasing major and
+minor number sizes. See the section on "Allocation of Device Numbers"
+for details on maintaining compatibility with userspace.
+
+Solving this requires a kernel change.
+
+Since writing this, the kernel has been modified so that the SCSI disc
+driver has more major numbers allocated to it and now supports up to
+128 discs. Since these major numbers are non-contiguous (a result of
+unplanned expansion), the implementation is a little more cumbersome
+than originally.
+
+Just like the changes to IPv4 to fix impending limitations in the
+address space, people find ways around the limitations. In the long
+run, however, solutions like IPv6 or devfs can't be put off forever.
+
+Read-only root filesystem
+
+Having your device nodes on the root filesystem means that you can't
+operate properly with a read-only root filesystem. This is because you
+want to change ownerships and protections of tty devices. Existing
+practice prevents you using a CD-ROM as your root filesystem for a
+*real* system. Sure, you can boot off a CD-ROM, but you can't change
+tty ownerships, so it's only good for installing.
+
+Also, you can't use a shared NFS root filesystem for a cluster of
+discless Linux machines (having tty ownerships changed on a common
+/dev is not good). Nor can you embed your root filesystem in a
+ROM-FS.
+
+You can get around this by creating a RAMDISC at boot time, making
+an ext2 filesystem in it, mounting it somewhere and copying the
+contents of /dev into it, then unmounting it and mounting it over
+/dev.
+
+A devfs is a cleaner way of solving this.
+
+Non-Unix root filesystem
+
+Non-Unix filesystems (such as NTFS) can't be used for a root
+filesystem because they variously don't support character and block
+special files or symbolic links. You can't have a separate disc-based
+or RAMDISC-based filesystem mounted on /dev because you need device
+nodes before you can mount these. Devfs can be mounted without any
+device nodes. Devlinks won't work because symlinks aren't supported.
+An alternative solution is to use initrd to mount a RAMDISC initial
+root filesystem (which is populated with a minimal set of device
+nodes), and then construct a new /dev in another RAMDISC, and finally
+switch to your non-Unix root filesystem. This requires clever boot
+scripts and a fragile and conceptually complex boot procedure.
+
+Devfs solves this in a robust and conceptually simple way.
+
+PTY security
+
+Current pseudo-tty (pty) devices are owned by root and read-writable
+by everyone. The user of a pty-pair cannot change
+ownership/protections without being suid-root.
+
+This could be solved with a secure user-space daemon which runs as
+root and does the actual creation of pty-pairs. Such a daemon would
+require modification to *every* programme that wants to use this new
+mechanism. It also slows down creation of pty-pairs.
+
+An alternative is to create a new open_pty() syscall which does much
+the same thing as the user-space daemon. Once again, this requires
+modifications to pty-handling programmes.
+
+The devfs solution allows a device driver to "tag" certain device
+files so that when an unopened device is opened, the ownerships are
+changed to the current euid and egid of the opening process, and the
+protections are changed to the default registered by the driver. When
+the device is closed ownership is set back to root and protections are
+set back to read-write for everybody. No programme need be changed.
+The devpts filesystem provides this auto-ownership feature for Unix98
+ptys. It doesn't support old-style pty devices, nor does it have all
+the other features of devfs.
+
+Intelligent device management
+
+Devfs implements a simple yet powerful protocol for communication with
+a device management daemon (devfsd) which runs in user space. It is
+possible to send a message (either synchronously or asynchronously) to
+devfsd on any event, such as registration/unregistration of device
+entries, opening and closing devices, looking up inodes, scanning
+directories and more. This has many possibilities. Some of these are
+already implemented. See:
+
+
+http://www.atnf.csiro.au/~rgooch/linux/
+
+Device entry registration events can be used by devfsd to change
+permissions of newly-created device nodes. This is one mechanism to
+control device permissions.
+
+Device entry registration/unregistration events can be used to run
+programmes or scripts. This can be used to provide automatic mounting
+of filesystems when a new block device media is inserted into the
+drive.
+
+Asynchronous device open and close events can be used to implement
+clever permissions management. For example, the default permissions on
+/dev/dsp do not allow everybody to read from the device. This is
+sensible, as you don't want some remote user recording what you say at
+your console. However, the console user is also prevented from
+recording. This behaviour is not desirable. With asynchronous device
+open and close events, you can have devfsd run a programme or script
+when console devices are opened to change the ownerships for *other*
+device nodes (such as /dev/dsp). On closure, you can run a different
+script to restore permissions. An advantage of this scheme over
+modifying the C library tty handling is that this works even if your
+programme crashes (how many times have you seen the utmp database with
+lingering entries for non-existent logins?).
+
+Synchronous device open events can be used to perform intelligent
+device access protections. Before the device driver open() method is
+called, the daemon must first validate the open attempt, by running an
+external programme or script. This is far more flexible than access
+control lists, as access can be determined on the basis of other
+system conditions instead of just the UID and GID.
+
+Inode lookup events can be used to authenticate module autoload
+requests. Instead of using kmod directly, the event is sent to
+devfsd which can implement an arbitrary authentication before loading
+the module itself.
+
+Inode lookup events can also be used to construct arbitrary
+namespaces, without having to resort to populating devfs with symlinks
+to devices that don't exist.
+
+Speculative Device Scanning
+
+Consider an application (like cdparanoia) that wants to find all
+CD-ROM devices on the system (SCSI, IDE and other types), whether or
+not their respective modules are loaded. The application must
+speculatively open certain device nodes (such as /dev/sr0 for the SCSI
+CD-ROMs) in order to make sure the module is loaded. This requires
+that all Linux distributions follow the standard device naming scheme
+(last time I looked RedHat did things differently). Devfs solves the
+naming problem.
+
+The same application also wants to see which devices are actually
+available on the system. With the existing system it needs to read the
+/dev directory and speculatively open each /dev/sr* device to
+determine if the device exists or not. With a large /dev this is an
+inefficient operation, especially if there are many /dev/sr* nodes. A
+solution like scsidev could reduce the number of /dev/sr* entries (but
+of course that also requires all that inefficient directory scanning).
+
+With devfs, the application can open the /dev/sr directory
+(which triggers the module autoloading if required), and proceed to
+read /dev/sr. Since only the available devices will have
+entries, there are no inefficencies in directory scanning or device
+openings.
+
+-----------------------------------------------------------------------------
+
+Who else does it?
+
+FreeBSD has a devfs implementation. Solaris and AIX each have a
+pseudo-devfs (something akin to scsidev but for all devices, with some
+unspecified kernel support). BeOS, Plan9 and QNX also have it. SGI's
+IRIX 6.4 and above also have a device filesystem.
+
+While we shouldn't just automatically do something because others do
+it, we should not ignore the work of others either. FreeBSD has a lot
+of competent people working on it, so their opinion should not be
+blithely ignored.
+
+-----------------------------------------------------------------------------
+
+
+How it works
+
+Registering device entries
+
+For every entry (device node) in a devfs-based /dev a driver must call
+devfs_register(). This adds the name of the device entry, the
+file_operations structure pointer and a few other things to an
+internal table. Device entries may be added and removed at any
+time. When a device entry is registered, it automagically appears in
+any mounted devfs'.
+
+Inode lookup
+
+When a lookup operation on an entry is performed and if there is no
+driver information for that entry devfs will attempt to call
+devfsd. If still no driver information can be found then a negative
+dentry is yielded and the next stage operation will be called by the
+VFS (such as create() or mknod() inode methods). If driver information
+can be found, an inode is created (if one does not exist already) and
+all is well.
+
+Manually creating device nodes
+
+The mknod() method allows you to create an ordinary named pipe in the
+devfs, or you can create a character or block special inode if one
+does not already exist. You may wish to create a character or block
+special inode so that you can set permissions and ownership. Later, if
+a device driver registers an entry with the same name, the
+permissions, ownership and times are retained. This is how you can set
+the protections on a device even before the driver is loaded. Once you
+create an inode it appears in the directory listing.
+
+Unregistering device entries
+
+A device driver calls devfs_unregister() to unregister an entry.
+
+Chroot() gaols
+
+2.2.x kernels
+
+The semantics of inode creation are different when devfs is mounted
+with the "explicit" option. Now, when a device entry is registered, it
+will not appear until you use mknod() to create the device. It doesn't
+matter if you mknod() before or after the device is registered with
+devfs_register(). The purpose of this behaviour is to support
+chroot(2) gaols, where you want to mount a minimal devfs inside the
+gaol. Only the devices you specifically want to be available (through
+your mknod() setup) will be accessible.
+
+2.4.x kernels
+
+As of kernel 2.3.99, the VFS has had the ability to rebind parts of
+the global filesystem namespace into another part of the namespace.
+This now works even at the leaf-node level, which means that
+individual files and device nodes may be bound into other parts of the
+namespace. This is like making links, but better, because it works
+across filesystems (unlike hard links) and works through chroot()
+gaols (unlike symbolic links).
+
+Because of these improvements to the VFS, the multi-mount capability
+in devfs is no longer needed. The administrator may create a minimal
+device tree inside a chroot(2) gaol by using VFS bindings. As this
+provides most of the features of the devfs multi-mount capability, I
+removed the multi-mount support code (after issuing an RFC). This
+yielded code size reductions and simplifications.
+
+If you want to construct a minimal chroot() gaol, the following
+command should suffice:
+
+mount --bind /dev/null /gaol/dev/null
+
+
+Repeat for other device nodes you want to expose. Simple!
+
+-----------------------------------------------------------------------------
+
+
+Operational issues
+
+
+Instructions for the impatient
+
+Nobody likes reading documentation. People just want to get in there
+and play. So this section tells you quickly the steps you need to take
+to run with devfs mounted over /dev. Skip these steps and you will end
+up with a nearly unbootable system. Subsequent sections describe the
+issues in more detail, and discuss non-essential configuration
+options.
+
+Devfsd
+OK, if you're reading this, I assume you want to play with
+devfs. First you should ensure that /usr/src/linux contains a
+recent kernel source tree. Then you need to compile devfsd, the device
+management daemon, available at
+
+http://www.atnf.csiro.au/~rgooch/linux/.
+Because the kernel has a naming scheme
+which is quite different from the old naming scheme, you need to
+install devfsd so that software and configuration files that use the
+old naming scheme will not break.
+
+Compile and install devfsd. You will be provided with a default
+configuration file /etc/devfsd.conf which will provide
+compatibility symlinks for the old naming scheme. Don't change this
+config file unless you know what you're doing. Even if you think you
+do know what you're doing, don't change it until you've followed all
+the steps below and booted a devfs-enabled system and verified that it
+works.
+
+Now edit your main system boot script so that devfsd is started at the
+very beginning (before any filesystem
+checks). /etc/rc.d/rc.sysinit is often the main boot script
+on systems with SysV-style boot scripts. On systems with BSD-style
+boot scripts it is often /etc/rc. Also check
+/sbin/rc.
+
+NOTE that the line you put into the boot
+script should be exactly:
+
+/sbin/devfsd /dev
+
+DO NOT use some special daemon-launching
+programme, otherwise the boot script may not wait for devfsd to finish
+initialising.
+
+System Libraries
+There may still be some problems because of broken software making
+assumptions about device names. In particular, some software does not
+handle devices which are symbolic links. If you are running a libc 5
+based system, install libc 5.4.44 (if you have libc 5.4.46, go back to
+libc 5.4.44, which is actually correct). If you are running a glibc
+based system, make sure you have glibc 2.1.3 or later.
+
+/etc/securetty
+PAM (Pluggable Authentication Modules) is supposed to be a flexible
+mechanism for providing better user authentication and access to
+services. Unfortunately, it's also fragile, complex and undocumented
+(check out RedHat 6.1, and probably other distributions as well). PAM
+has problems with symbolic links. Append the following lines to your
+/etc/securetty file:
+
+vc/1
+vc/2
+vc/3
+vc/4
+vc/5
+vc/6
+vc/7
+vc/8
+
+This will not weaken security. If you have a version of util-linux
+earlier than 2.10.h, please upgrade to 2.10.h or later. If you
+absolutely cannot upgrade, then also append the following lines to
+your /etc/securetty file:
+
+1
+2
+3
+4
+5
+6
+7
+8
+
+This may potentially weaken security by allowing root logins over the
+network (a password is still required, though). However, since there
+are problems with dealing with symlinks, I'm suspicious of the level
+of security offered in any case.
+
+XFree86
+While not essential, it's probably a good idea to upgrade to XFree86
+4.0, as patches went in to make it more devfs-friendly. If you don't,
+you'll probably need to apply the following patch to
+/etc/security/console.perms so that ordinary users can run
+startx. Note that not all distributions have this file (e.g. Debian),
+so if it's not present, don't worry about it.
+
+--- /etc/security/console.perms.orig    Sat Apr 17 16:26:47 1999 
++++ /etc/security/console.perms Fri Feb 25 23:53:55 2000 
+@@ -14,7 +14,7 @@ 
+ # man 5 console.perms 
+
+ # file classes -- these are regular expressions 
+-<console>=tty[0-9][0-9]* :[0-9]\.[0-9] :[0-9] 
++<console>=tty[0-9][0-9]* vc/[0-9][0-9]* :[0-9]\.[0-9] :[0-9] 
+
+ # device classes -- these are shell-style globs 
+ <floppy>=/dev/fd[0-1]* 
+
+If the patch does not apply, then change the line:
+
+<console>=tty[0-9][0-9]* :[0-9]\.[0-9] :[0-9]
+
+with:
+
+<console>=tty[0-9][0-9]* vc/[0-9][0-9]* :[0-9]\.[0-9] :[0-9]
+
+
+Disable devpts
+I've had a report of devpts mounted on /dev/pts not working
+correctly. Since devfs will also manage /dev/pts, there is no
+need to mount devpts as well. You should either edit your
+/etc/fstab so devpts is not mounted, or disable devpts from
+your kernel configuration.
+
+Unsupported drivers
+Not all drivers have devfs support. If you depend on one of these
+drivers, you will need to create a script or tarfile that you can use
+at boot time to create device nodes as appropriate. There is a
+section which describes this. Another
+section lists the drivers which have
+devfs support.
+
+/dev/mouse
+
+Many disributions configure /dev/mouse to be the mouse device
+for XFree86 and GPM. I actually think this is a bad idea, because it
+adds another level of indirection. When looking at a config file, if
+you see /dev/mouse you're left wondering which mouse
+is being referred to. Hence I recommend putting the actual mouse
+device (for example /dev/psaux) into your
+/etc/X11/XF86Config file (and similarly for the GPM
+configuration file).
+
+Alternatively, use the same technique used for unsupported drivers
+described above.
+
+The Kernel
+Finally, you need to make sure devfs is compiled into your kernel. Set
+CONFIG_EXPERIMENTAL=y, CONFIG_DEVFS_FS=y and CONFIG_DEVFS_MOUNT=y by
+using favourite configuration tool (i.e. make config or
+make xconfig) and then make clean and then recompile your kernel and 
+modules. At boot, devfs will be mounted onto /dev.
+
+If you encounter problems booting (for example if you forgot a
+configuration step), you can pass devfs=nomount at the kernel
+boot command line. This will prevent the kernel from mounting devfs at
+boot time onto /dev.
+
+In general, a kernel built with CONFIG_DEVFS_FS=y but without mounting
+devfs onto /dev is completely safe, and requires no
+configuration changes. One exception to take note of is when
+LABEL= directives are used in /etc/fstab. In this
+case you will be unable to boot properly. This is because the
+mount(8) programme uses /proc/partitions as part of
+the volume label search process, and the device names it finds are not
+available, because setting CONFIG_DEVFS_FS=y changes the names in
+/proc/partitions, irrespective of whether devfs is mounted.
+
+Now you've finished all the steps required. You're now ready to boot
+your shiny new kernel. Enjoy.
+
+Changing the configuration
+
+OK, you've now booted a devfs-enabled system, and everything works.
+Now you may feel like changing the configuration (common targets are
+/etc/fstab and /etc/devfsd.conf). Since you have a
+system that works, if you make any changes and it doesn't work, you
+now know that you only have to restore your configuration files to the
+default and it will work again.
+
+
+Permissions persistence across reboots
+
+If you don't use mknod(2) to create a device file, nor use chmod(2) or
+chown(2) to change the ownerships/permissions, the inode ctime will
+remain at 0 (the epoch, 12 am, 1-JAN-1970, GMT). Anything with a ctime
+later than this has had it's ownership/permissions changed. Hence, a
+simple script or programme may be used to tar up all changed inodes,
+prior to shutdown. Although effective, many consider this approach a
+kludge.
+
+A much better approach is to use devfsd to save and restore
+permissions. It may be configured to record changes in permissions and
+will save them in a database (in fact a directory tree), and restore
+these upon boot. This is an efficient method and results in immediate
+saving of current permissions (unlike the tar approach, which saves
+permissions at some unspecified future time).
+
+The default configuration file supplied with devfsd has config entries
+which you may uncomment to enable persistence management.
+
+If you decide to use the tar approach anyway, be aware that tar will
+first unlink(2) an inode before creating a new device node. The
+unlink(2) has the effect of breaking the connection between a devfs
+entry and the device driver. If you use the "devfs=only" boot option,
+you lose access to the device driver, requiring you to reload the
+module. I consider this a bug in tar (there is no real need to
+unlink(2) the inode first).
+
+Alternatively, you can use devfsd to provide more sophisticated
+management of device permissions. You can use devfsd to store
+permissions for whole groups of devices with a single configuration
+entry, rather than the conventional single entry per device entry.
+
+Permissions database stored in mounted-over /dev
+
+If you wish to save and restore your device permissions into the
+disc-based /dev while still mounting devfs onto /dev
+you may do so. This requires a 2.4.x kernel (in fact, 2.3.99 or
+later), which has the VFS binding facility. You need to do the
+following to set this up:
+
+
+
+make sure the kernel does not mount devfs at boot time
+
+
+make sure you have a correct /dev/console entry in your
+root file-system (where your disc-based /dev lives)
+
+create the /dev-state directory
+
+
+add the following lines near the very beginning of your boot
+scripts:
+
+mount --bind /dev /dev-state
+mount -t devfs none /dev
+devfsd /dev
+
+
+
+
+add the following lines to your /etc/devfsd.conf file:
+
+REGISTER       ^pt[sy]         IGNORE
+CREATE         ^pt[sy]         IGNORE
+CHANGE         ^pt[sy]         IGNORE
+DELETE         ^pt[sy]         IGNORE
+REGISTER       .*              COPY    /dev-state/$devname $devpath
+CREATE         .*              COPY    $devpath /dev-state/$devname
+CHANGE         .*              COPY    $devpath /dev-state/$devname
+DELETE         .*              CFUNCTION GLOBAL unlink /dev-state/$devname
+RESTORE                /dev-state
+
+Note that the sample devfsd.conf file contains these lines,
+as well as other sample configurations you may find useful. See the
+devfsd distribution
+
+
+reboot.
+
+
+
+
+Permissions database stored in normal directory
+
+If you are using an older kernel which doesn't support VFS binding,
+then you won't be able to have the permissions database in a
+mounted-over /dev. However, you can still use a regular
+directory to store the database. The sample /etc/devfsd.conf
+file above may still be used. You will need to create the
+/dev-state directory prior to installing devfsd. If you have
+old permissions in /dev, then just copy (or move) the device
+nodes over to the new directory.
+
+Which method is better?
+
+The best method is to have the permissions database stored in the
+mounted-over /dev. This is because you will not need to copy
+device nodes over to /dev-state, and because it allows you to
+switch between devfs and non-devfs kernels, without requiring you to
+copy permissions between /dev-state (for devfs) and
+/dev (for non-devfs).
+
+
+Dealing with drivers without devfs support
+
+Currently, not all device drivers in the kernel have been modified to
+use devfs. Device drivers which do not yet have devfs support will not
+automagically appear in devfs. The simplest way to create device nodes
+for these drivers is to unpack a tarfile containing the required
+device nodes. You can do this in your boot scripts. All your drivers
+will now work as before.
+
+Hopefully for most people devfs will have enough support so that they
+can mount devfs directly over /dev without losing most functionality
+(i.e. losing access to various devices). As of 22-JAN-1998 (devfs
+patch version 10) I am now running this way. All the devices I have
+are available in devfs, so I don't lose anything.
+
+WARNING: if your configuration requires the old-style device names
+(i.e. /dev/hda1 or /dev/sda1), you must install devfsd and configure
+it to maintain compatibility entries. It is almost certain that you
+will require this. Note that the kernel creates a compatibility entry
+for the root device, so you don't need initrd.
+
+Note that you no longer need to mount devpts if you use Unix98 PTYs,
+as devfs can manage /dev/pts itself. This saves you some RAM, as you
+don't need to compile and install devpts. Note that some versions of
+glibc have a bug with Unix98 pty handling on devfs systems. Contact
+the glibc maintainers for a fix. Glibc 2.1.3 has the fix.
+
+Note also that apart from editing /etc/fstab, other things will need
+to be changed if you *don't* install devfsd. Some software (like the X
+server) hard-wire device names in their source. It really is much
+easier to install devfsd so that compatibility entries are created.
+You can then slowly migrate your system to using the new device names
+(for example, by starting with /etc/fstab), and then limiting the
+compatibility entries that devfsd creates.
+
+IF YOU CONFIGURE TO MOUNT DEVFS AT BOOT, MAKE SURE YOU INSTALL DEVFSD
+BEFORE YOU BOOT A DEVFS-ENABLED KERNEL!
+
+Now that devfs has gone into the 2.3.46 kernel, I'm getting a lot of
+reports back. Many of these are because people are trying to run
+without devfsd, and hence some things break. Please just run devfsd if
+things break. I want to concentrate on real bugs rather than
+misconfiguration problems at the moment. If people are willing to fix
+bugs/false assumptions in other code (i.e. glibc, X server) and submit
+that to the respective maintainers, that would be great.
+
+
+All the way with Devfs
+
+The devfs kernel patch creates a rationalised device tree. As stated
+above, if you want to keep using the old /dev naming scheme,
+you just need to configure devfsd appopriately (see the man
+page). People who prefer the old names can ignore this section. For
+those of us who like the rationalised names and an uncluttered
+/dev, read on.
+
+If you don't run devfsd, or don't enable compatibility entry
+management, then you will have to configure your system to use the new
+names. For example, you will then need to edit your
+/etc/fstab to use the new disc naming scheme. If you want to
+be able to boot non-devfs kernels, you will need compatibility
+symlinks in the underlying disc-based /dev pointing back to
+the old-style names for when you boot a kernel without devfs.
+
+You can selectively decide which devices you want compatibility
+entries for. For example, you may only want compatibility entries for
+BSD pseudo-terminal devices (otherwise you'll have to patch you C
+library or use Unix98 ptys instead). It's just a matter of putting in
+the correct regular expression into /dev/devfsd.conf.
+
+There are other choices of naming schemes that you may prefer. For
+example, I don't use the kernel-supplied
+names, because they are too verbose. A common misconception is
+that the kernel-supplied names are meant to be used directly in
+configuration files. This is not the case. They are designed to
+reflect the layout of the devices attached and to provide easy
+classification.
+
+If you like the kernel-supplied names, that's fine. If you don't then
+you should be using devfsd to construct a namespace more to your
+liking. Devfsd has built-in code to construct a
+namespace that is both logical and easy to
+manage. In essence, it creates a convenient abbreviation of the
+kernel-supplied namespace.
+
+You are of course free to build your own namespace. Devfsd has all the
+infrastructure required to make this easy for you. All you need do is
+write a script. You can even write some C code and devfsd can load the
+shared object as a callable extension.
+
+
+Other Issues
+
+The init programme
+Another thing to take note of is whether your init programme
+creates a Unix socket /dev/telinit. Some versions of init
+create /dev/telinit so that the telinit programme can
+communicate with the init process. If you have such a system you need
+to make sure that devfs is mounted over /dev *before* init
+starts. In other words, you can't leave the mounting of devfs to
+/etc/rc, since this is executed after init. Other
+versions of init require a named pipe /dev/initctl
+which must exist *before* init starts. Once again, you need to
+mount devfs and then create the named pipe *before* init
+starts.
+
+The default behaviour now is not to mount devfs onto /dev at
+boot time for 2.3.x and later kernels. You can correct this with the
+"devfs=mount" boot option. This solves any problems with init,
+and also prevents the dreaded:
+
+Cannot open initial console
+
+message. For 2.2.x kernels where you need to apply the devfs patch,
+the default is to mount.
+
+If you have automatic mounting of devfs onto /dev then you
+may need to create /dev/initctl in your boot scripts. The
+following lines should suffice:
+
+mknod /dev/initctl p
+kill -SIGUSR1 1       # tell init that /dev/initctl now exists
+
+Alternatively, if you don't want the kernel to mount devfs onto
+/dev then you could use the following procedure is a
+guideline for how to get around /dev/initctl problems:
+
+# cd /sbin
+# mv init init.real
+# cat > init
+#! /bin/sh
+mount -n -t devfs none /dev
+mknod /dev/initctl p
+exec /sbin/init.real $*
+[control-D]
+# chmod a+x init
+
+Note that newer versions of init create /dev/initctl
+automatically, so you don't have to worry about this.
+
+Module autoloading
+You will need to configure devfsd to enable module
+autoloading. The following lines should be placed in your
+/etc/devfsd.conf file:
+
+LOOKUP .*              MODLOAD
+
+
+As of devfsd-v1.3.10, a generic /etc/modules.devfs
+configuration file is installed, which is used by the MODLOAD
+action. This should be sufficient for most configurations. If you
+require further configuration, edit your /etc/modules.conf
+file. The way module autoloading work with devfs is:
+
+
+a process attempts to lookup a device node (e.g. /dev/fred)
+
+
+if that device node does not exist, the full pathname is passed to
+devfsd as a string
+
+
+devfsd will pass the string to the modprobe programme (provided the
+configuration line shown above is present), and specifies that
+/etc/modules.devfs is the configuration file
+
+
+/etc/modules.devfs includes /etc/modules.conf to
+access local configurations
+
+modprobe will search it's configuration files, looking for an alias
+that translates the pathname into a module name
+
+
+the translated pathname is then used to load the module.
+
+
+If you wanted a lookup of /dev/fred to load the
+mymod module, you would require the following configuration
+line in /etc/modules.conf:
+
+alias    /dev/fred    mymod
+
+The /etc/modules.devfs configuration file provides many such
+aliases for standard device names. If you look closely at this file,
+you will note that some modules require multiple alias configuration
+lines. This is required to support module autoloading for old and new
+device names.
+
+Mounting root off a devfs device
+If you wish to mount root off a devfs device when you pass the
+"devfs=only" boot option, then you need to pass in the
+"root=<device>" option to the kernel when booting. If you use
+LILO, then you must have this in lilo.conf:
+
+append = "root=<device>"
+
+Surprised? Yep, so was I. It turns out if you have (as most people
+do):
+
+root = <device>
+
+
+then LILO will determine the device number of <device> and will
+write that device number into a special place in the kernel image
+before starting the kernel, and the kernel will use that device number
+to mount the root filesystem. So, using the "append" variety ensures
+that LILO passes the root filesystem device as a string, which devfs
+can then use.
+
+Note that this isn't an issue if you don't pass "devfs=only".
+
+TTY issues
+The ttyname(3) function in some versions of the C library makes
+false assumptions about device entries which are symbolic links.  The
+tty(1) programme is one that depends on this function.  I've
+written a patch to libc 5.4.43 which fixes this. This has been
+included in libc 5.4.44 and a similar fix is in glibc 2.1.3.
+
+
+Kernel Naming Scheme
+
+The kernel provides a default naming scheme. This scheme is designed
+to make it easy to search for specific devices or device types, and to
+view the available devices. Some device types (such as hard discs),
+have a directory of entries, making it easy to see what devices of
+that class are available. Often, the entries are symbolic links into a
+directory tree that reflects the topology of available devices. The
+topological tree is useful for finding how your devices are arranged.
+
+Below is a list of the naming schemes for the most common drivers. A
+list of reserved device names is
+available for reference. Please send email to
+rgooch@atnf.csiro.au to obtain an allocation. Please be
+patient (the maintainer is busy). An alternative name may be allocated
+instead of the requested name, at the discretion of the maintainer.
+
+Disc Devices
+
+All discs, whether SCSI, IDE or whatever, are placed under the
+/dev/discs hierarchy:
+
+       /dev/discs/disc0        first disc
+       /dev/discs/disc1        second disc
+
+
+Each of these entries is a symbolic link to the directory for that
+device. The device directory contains:
+
+       disc    for the whole disc
+       part*   for individual partitions
+
+
+CD-ROM Devices
+
+All CD-ROMs, whether SCSI, IDE or whatever, are placed under the
+/dev/cdroms hierarchy:
+
+       /dev/cdroms/cdrom0      first CD-ROM
+       /dev/cdroms/cdrom1      second CD-ROM
+
+
+Each of these entries is a symbolic link to the real device entry for
+that device.
+
+Tape Devices
+
+All tapes, whether SCSI, IDE or whatever, are placed under the
+/dev/tapes hierarchy:
+
+       /dev/tapes/tape0        first tape
+       /dev/tapes/tape1        second tape
+
+
+Each of these entries is a symbolic link to the directory for that
+device. The device directory contains:
+
+       mt                      for mode 0
+       mtl                     for mode 1
+       mtm                     for mode 2
+       mta                     for mode 3
+       mtn                     for mode 0, no rewind
+       mtln                    for mode 1, no rewind
+       mtmn                    for mode 2, no rewind
+       mtan                    for mode 3, no rewind
+
+
+SCSI Devices
+
+To uniquely identify any SCSI device requires the following
+information:
+
+  controller   (host adapter)
+  bus          (SCSI channel)
+  target       (SCSI ID)
+  unit         (Logical Unit Number)
+
+
+All SCSI devices are placed under /dev/scsi (assuming devfs
+is mounted on /dev). Hence, a SCSI device with the following
+parameters: c=1,b=2,t=3,u=4 would appear as:
+
+       /dev/scsi/host1/bus2/target3/lun4       device directory
+
+
+Inside this directory, a number of device entries may be created,
+depending on which SCSI device-type drivers were installed.
+
+See the section on the disc naming scheme to see what entries the SCSI
+disc driver creates.
+
+See the section on the tape naming scheme to see what entries the SCSI
+tape driver creates.
+
+The SCSI CD-ROM driver creates:
+
+       cd
+
+
+The SCSI generic driver creates:
+
+       generic
+
+
+IDE Devices
+
+To uniquely identify any IDE device requires the following
+information:
+
+  controller
+  bus          (aka. primary/secondary)
+  target       (aka. master/slave)
+  unit
+
+
+All IDE devices are placed under /dev/ide, and uses a similar
+naming scheme to the SCSI subsystem.
+
+XT Hard Discs
+
+All XT discs are placed under /dev/xd. The first XT disc has
+the directory /dev/xd/disc0.
+
+TTY devices
+
+The tty devices now appear as:
+
+  New name                   Old-name                   Device Type
+  --------                   --------                   -----------
+  /dev/tts/{0,1,...}         /dev/ttyS{0,1,...}         Serial ports
+  /dev/cua/{0,1,...}         /dev/cua{0,1,...}          Call out devices
+  /dev/vc/0                  /dev/tty                   Current virtual console
+  /dev/vc/{1,2,...}          /dev/tty{1...63}           Virtual consoles
+  /dev/vcc/{0,1,...}         /dev/vcs{1...63}           Virtual consoles
+  /dev/pty/m{0,1,...}        /dev/ptyp??                PTY masters
+  /dev/pty/s{0,1,...}        /dev/ttyp??                PTY slaves
+
+
+RAMDISCS
+
+The RAMDISCS are placed in their own directory, and are named thus:
+
+  /dev/rd/{0,1,2,...}
+
+
+Meta Devices
+
+The meta devices are placed in their own directory, and are named
+thus:
+
+  /dev/md/{0,1,2,...}
+
+
+Floppy discs
+
+Floppy discs are placed in the /dev/floppy directory.
+
+Loop devices
+
+Loop devices are placed in the /dev/loop directory.
+
+Sound devices
+
+Sound devices are placed in the /dev/sound directory
+(audio, sequencer, ...).
+
+
+Devfsd Naming Scheme
+
+Devfsd provides a naming scheme which is a convenient abbreviation of
+the kernel-supplied namespace. In some
+cases, the kernel-supplied naming scheme is quite convenient, so
+devfsd does not provide another naming scheme. The convenience names
+that devfsd creates are in fact the same names as the original devfs
+kernel patch created (before Linus mandated the Big Name
+Change). These are referred to as "new compatibility entries".
+
+In order to configure devfsd to create these convenience names, the
+following lines should be placed in your /etc/devfsd.conf:
+
+REGISTER       .*              MKNEWCOMPAT
+UNREGISTER     .*              RMNEWCOMPAT
+
+This will cause devfsd to create (and destroy) symbolic links which
+point to the kernel-supplied names.
+
+SCSI Hard Discs
+
+All SCSI discs are placed under /dev/sd (assuming devfs is
+mounted on /dev). Hence, a SCSI disc with the following
+parameters: c=1,b=2,t=3,u=4 would appear as:
+
+       /dev/sd/c1b2t3u4        for the whole disc
+       /dev/sd/c1b2t3u4p5      for the 5th partition
+       /dev/sd/c1b2t3u4p5s6    for the 6th slice in the 5th partition
+
+
+SCSI Tapes
+
+All SCSI tapes are placed under /dev/st. A similar naming
+scheme is used as for SCSI discs. A SCSI tape with the
+parameters:c=1,b=2,t=3,u=4 would appear as:
+
+       /dev/st/c1b2t3u4m0      for mode 0
+       /dev/st/c1b2t3u4m1      for mode 1
+       /dev/st/c1b2t3u4m2      for mode 2
+       /dev/st/c1b2t3u4m3      for mode 3
+       /dev/st/c1b2t3u4m0n     for mode 0, no rewind
+       /dev/st/c1b2t3u4m1n     for mode 1, no rewind
+       /dev/st/c1b2t3u4m2n     for mode 2, no rewind
+       /dev/st/c1b2t3u4m3n     for mode 3, no rewind
+
+
+SCSI CD-ROMs
+
+All SCSI CD-ROMs are placed under /dev/sr. A similar naming
+scheme is used as for SCSI discs. A SCSI CD-ROM with the
+parameters:c=1,b=2,t=3,u=4 would appear as:
+
+       /dev/sr/c1b2t3u4
+
+
+SCSI Generic Devices
+
+The generic (aka. raw) interface for all SCSI devices are placed under
+/dev/sg. A similar naming scheme is used as for SCSI discs. A
+SCSI generic device with the parameters:c=1,b=2,t=3,u=4 would appear
+as:
+
+       /dev/sg/c1b2t3u4
+
+
+IDE Hard Discs
+
+All IDE discs are placed under /dev/ide/hd, using a similar
+convention to SCSI discs. The following mappings exist between the new
+and the old names:
+
+       /dev/hda        /dev/ide/hd/c0b0t0u0
+       /dev/hdb        /dev/ide/hd/c0b0t1u0
+       /dev/hdc        /dev/ide/hd/c0b1t0u0
+       /dev/hdd        /dev/ide/hd/c0b1t1u0
+
+
+IDE Tapes
+
+A similar naming scheme is used as for IDE discs. The entries will
+appear in the /dev/ide/mt directory.
+
+IDE CD-ROM
+
+A similar naming scheme is used as for IDE discs. The entries will
+appear in the /dev/ide/cd directory.
+
+IDE Floppies
+
+A similar naming scheme is used as for IDE discs. The entries will
+appear in the /dev/ide/fd directory.
+
+XT Hard Discs
+
+All XT discs are placed under /dev/xd. The first XT disc
+would appear as /dev/xd/c0t0.
+
+
+Old Compatibility Names
+
+The old compatibility names are the legacy device names, such as
+/dev/hda, /dev/sda, /dev/rtc and so on.
+Devfsd can be configured to create compatibility symlinks so that you
+may continue to use the old names in your configuration files and so
+that old applications will continue to function correctly.
+
+In order to configure devfsd to create these legacy names, the
+following lines should be placed in your /etc/devfsd.conf:
+
+REGISTER       .*              MKOLDCOMPAT
+UNREGISTER     .*              RMOLDCOMPAT
+
+This will cause devfsd to create (and destroy) symbolic links which
+point to the kernel-supplied names.
+
+
+-----------------------------------------------------------------------------
+
+
+Device drivers currently ported
+
+- All miscellaneous character devices support devfs (this is done
+  transparently through misc_register())
+
+- SCSI discs and generic hard discs
+
+- Character memory devices (null, zero, full and so on)
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- Loop devices (/dev/loop?)
+ 
+- TTY devices (console, serial ports, terminals and pseudo-terminals)
+  Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- SCSI tapes (/dev/scsi and /dev/tapes)
+
+- SCSI CD-ROMs (/dev/scsi and /dev/cdroms)
+
+- SCSI generic devices (/dev/scsi)
+
+- RAMDISCS (/dev/ram?)
+
+- Meta Devices (/dev/md*)
+
+- Floppy discs (/dev/floppy)
+
+- Parallel port printers (/dev/printers)
+
+- Sound devices (/dev/sound)
+  Thanks to Eric Dumas <dumas@linux.eu.org> and
+  C. Scott Ananian <cananian@alumni.princeton.edu>
+
+- Joysticks (/dev/joysticks)
+
+- Sparc keyboard (/dev/kbd)
+
+- DSP56001 digital signal processor (/dev/dsp56k)
+
+- Apple Desktop Bus (/dev/adb)
+
+- Coda network file system (/dev/cfs*)
+
+- Virtual console capture devices (/dev/vcc)
+  Thanks to Dennis Hou <smilax@mindmeld.yi.org>
+
+- Frame buffer devices (/dev/fb)
+
+- Video capture devices (/dev/v4l)
+
+
+-----------------------------------------------------------------------------
+
+
+Allocation of Device Numbers
+
+Devfs allows you to write a driver which doesn't need to allocate a
+device number (major&minor numbers) for the internal operation of the
+kernel. However, there are a number of userspace programmes that use
+the device number as a unique handle for a device. An example is the
+find programme, which uses device numbers to determine whether
+an inode is on a different filesystem than another inode. The device
+number used is the one for the block device which a filesystem is
+using. To preserve compatibility with userspace programmes, block
+devices using devfs need to have unique device numbers allocated to
+them. Furthermore, POSIX specifies device numbers, so some kind of
+device number needs to be presented to userspace.
+
+The simplest option (especially when porting drivers to devfs) is to
+keep using the old major and minor numbers. Devfs will take whatever
+values are given for major&minor and pass them onto userspace.
+
+This device number is a 16 bit number, so this leaves plenty of space
+for large numbers of discs and partitions. This scheme can also be
+used for character devices, in particular the tty devices, which are
+currently limited to 256 pseudo-ttys (this limits the total number of
+simultaneous xterms and remote logins).  Note that the device number
+is limited to the range 36864-61439 (majors 144-239), in order to
+avoid any possible conflicts with existing official allocations.
+
+Please note that using dynamically allocated block device numbers may
+break the NFS daemons (both user and kernel mode), which expect dev_t
+for a given device to be constant over the lifetime of remote mounts.
+
+A final note on this scheme: since it doesn't increase the size of
+device numbers, there are no compatibility issues with userspace.
+
+-----------------------------------------------------------------------------
+
+
+Questions and Answers
+
+
+Making things work
+Alternatives to devfs
+What I don't like about devfs
+How to report bugs
+Strange kernel messages
+Compilation problems with devfsd
+
+
+
+Making things work
+
+Here are some common questions and answers.
+
+
+
+Devfsd doesn't start
+
+Make sure you have compiled and installed devfsd
+Make sure devfsd is being started from your boot
+scripts
+Make sure you have configured your kernel to enable devfs (see
+below)
+Make sure devfs is mounted (see below)
+
+
+Devfsd is not managing all my permissions
+
+Make sure you are capturing the appropriate events. For example,
+device entries created by the kernel generate REGISTER events,
+but those created by devfsd generate CREATE events.
+
+
+Devfsd is not capturing all REGISTER events
+
+See the previous entry: you may need to capture CREATE events.
+
+
+X will not start
+
+Make sure you followed the steps 
+outlined above.
+
+
+Why don't my network devices appear in devfs?
+
+This is not a bug. Network devices have their own, completely separate
+namespace. They are accessed via socket(2) and
+setsockopt(2) calls, and thus require no device nodes. I have
+raised the possibilty of moving network devices into the device
+namespace, but have had no response.
+
+
+How can I test if I have devfs compiled into my kernel?
+
+All filesystems built-in or currently loaded are listed in
+/proc/filesystems. If you see a devfs entry, then
+you know that devfs was compiled into your kernel. If you have
+correctly configured and rebuilt your kernel, then devfs will be
+built-in. If you think you've configured it in, but
+/proc/filesystems doesn't show it, you've made a mistake.
+Common mistakes include:
+
+Using a 2.2.x kernel without applying the devfs patch (if you
+don't know how to patch your kernel, use 2.4.x instead, don't bother
+asking me how to patch)
+Forgetting to set CONFIG_EXPERIMENTAL=y
+Forgetting to set CONFIG_DEVFS_FS=y
+Forgetting to set CONFIG_DEVFS_MOUNT=y (if you want devfs
+to be automatically mounted at boot)
+Editing your .config manually, instead of using make
+config or make xconfig
+Forgetting to run make dep; make clean after changing the
+configuration and before compiling
+Forgetting to compile your kernel and modules
+Forgetting to install your kernel
+Forgetting to install your modules
+
+Please check twice that you've done all these steps before sending in
+a bug report.
+
+
+
+How can I test if devfs is mounted on /dev?
+
+The device filesystem will always create an entry called
+".devfsd", which is used to communicate with the daemon. Even
+if the daemon is not running, this entry will exist. Testing for the
+existence of this entry is the approved method of determining if devfs
+is mounted or not. Note that the type of entry (i.e. regular file,
+character device, named pipe, etc.) may change without notice. Only
+the existence of the entry should be relied upon.
+
+
+When I start devfsd, I see the error:
+Error opening file: ".devfsd"   No such file or directory?
+
+This means that devfs is not mounted. Make sure you have devfs mounted.
+
+
+How do I mount devfs?
+
+First make sure you have devfs compiled into your kernel (see
+above). Then you will either need to:
+
+set CONFIG_DEVFS_MOUNT=y in your kernel config
+pass devfs=mount to your boot loader
+mount devfs manually in your boot scripts with:
+mount -t none devfs /dev
+
+
+
+Mount by volume LABEL=<label> doesn't work with
+devfs
+
+Most probably you are not mounting devfs onto /dev. What
+happens is that if your kernel config has CONFIG_DEVFS_FS=y
+then the contents of /proc/partitions will have the devfs
+names (such as scsi/host0/bus0/target0/lun0/part1). The
+contents of /proc/partitions are used by mount(8) when
+mounting by volume label. If devfs is not mounted on /dev,
+then mount(8) will fail to find devices. The solution is to
+make sure that devfs is mounted on /dev. See above for how to
+do that.
+
+
+I have extra or incorrect entries in /dev
+
+You may have stale entries in your dev-state area. Check for a
+RESTORE configuration line in your devfsd configuration
+(typically /etc/devfsd.conf). If you have this line, check
+the contents of the specified directory for stale entries. Remove
+any entries which are incorrect, then reboot.
+
+
+I get "Unable to open initial console" messages at boot
+
+This usually happens when you don't have devfs automounted onto
+/dev at boot time, and there is no valid
+/dev/console entry on your root file-system. Create a valid
+/dev/console device node.
+
+
+
+
+
+Alternatives to devfs
+
+I've attempted to collate all the anti-devfs proposals and explain
+their limitations. Under construction.
+
+
+Why not just pass device create/remove events to a daemon?
+
+Here the suggestion is to develop an API in the kernel so that devices
+can register create and remove events, and a daemon listens for those
+events. The daemon would then populate/depopulate /dev (which
+resides on disc).
+
+This has several limitations:
+
+
+it only works for modules loaded and unloaded (or devices inserted
+and removed) after the kernel has finished booting. Without a database
+of events, there is no way the daemon could fully populate
+/dev
+
+
+if you add a database to this scheme, the question is then how to
+present that database to user-space. If you make it a list of strings
+with embedded event codes which are passed through a pipe to the
+daemon, then this is only of use to the daemon. I would argue that the
+natural way to present this data is via a filesystem (since many of
+the events will be of a hierarchical nature), such as devfs.
+Presenting the data as a filesystem makes it easy for the user to see
+what is available and also makes it easy to write scripts to scan the
+"database"
+
+
+the tight binding between device nodes and drivers is no longer
+possible (requiring the otherwise perfectly avoidable
+table lookups)
+
+
+you cannot catch inode lookup events on /dev which means
+that module autoloading requires device nodes to be created. This is a
+problem, particularly for drivers where only a few inodes are created
+from a potentially large set
+
+
+this technique can't be used when the root FS is mounted
+read-only
+
+
+
+
+Just implement a better scsidev
+
+This suggestion involves taking the scsidev programme and
+extending it to scan for all devices, not just SCSI devices. The
+scsidev programme works by scanning /proc/scsi
+
+Problems:
+
+
+the kernel does not currently provide a list of all devices
+available. Not all drivers register entries in /proc or
+generate kernel messages
+
+
+there is no uniform mechanism to register devices other than the
+devfs API
+
+
+implementing such an API is then the same as the
+proposal above
+
+
+
+
+Put /dev on a ramdisc
+
+This suggestion involves creating a ramdisc and populating it with
+device nodes and then mounting it over /dev.
+
+Problems:
+
+
+
+this doesn't help when mounting the root filesystem, since you
+still need a device node to do that
+
+
+if you want to use this technique for the root device node as
+well, you need to use initrd. This complicates the booting sequence
+and makes it significantly harder to administer and configure. The
+initrd is essentially opaque, robbing the system administrator of easy
+configuration
+
+
+insufficient information is available to correctly populate the
+ramdisc. So we come back to the
+proposal above to "solve" this
+
+
+a ramdisc-based solution would take more kernel memory, since the
+backing store would be (at best) normal VFS inodes and dentries, which
+take 284 bytes and 112 bytes, respectively, for each entry. Compare
+that to 72 bytes for devfs
+
+
+
+
+Do nothing: there's no problem
+
+Sometimes people can be heard to claim that the existing scheme is
+fine. This is what they're ignoring:
+
+
+device number size (8 bits each for major and minor) is a real
+limitation, and must be fixed somehow. Systems with large numbers of
+SCSI devices, for example, will continue to consume the remaining
+unallocated major numbers. USB will also need to push beyond the 8 bit
+minor limitation
+
+
+simply increasing the device number size is insufficient. Apart
+from causing a lot of pain, it doesn't solve the management issues
+of a /dev with thousands or more device nodes
+
+
+ignoring the problem of a huge /dev will not make it go
+away, and dismisses the legitimacy of a large number of people who
+want a dynamic /dev
+
+
+the standard response then becomes: "write a device management
+daemon", which brings us back to the
+proposal above
+
+
+
+
+What I don't like about devfs
+
+Here are some common complaints about devfs, and some suggestions and
+solutions that may make it more palatable for you. I can't please
+everybody, but I do try :-)
+
+I hate the naming scheme
+
+First, remember that no naming scheme will please everybody. You hate
+the scheme, others love it. Who's to say who's right and who's wrong?
+Ultimately, the person who writes the code gets to choose, and what
+exists now is a combination of the choices made by the
+devfs author and the
+kernel maintainer (Linus).
+
+However, not all is lost. If you want to create your own naming
+scheme, it is a simple matter to write a standalone script, hack
+devfsd, or write a script called by devfsd. You can create whatever
+naming scheme you like.
+
+Further, if you want to remove all traces of the devfs naming scheme
+from /dev, you can mount devfs elsewhere (say
+/devfs) and populate /dev with links into
+/devfs. This population can be automated using devfsd if you
+wish.
+
+You can even use the VFS binding facility to make the links, rather
+than using symbolic links. This way, you don't even have to see the
+"destination" of these symbolic links.
+
+Devfs puts policy into the kernel
+
+There's already policy in the kernel. Device numbers are in fact
+policy (why should the kernel dictate what device numbers I use?).
+Face it, some policy has to be in the kernel. The real difference
+between device names as policy and device numbers as policy is that
+no one will use device numbers directly, because device
+numbers are devoid of meaning to humans and are ugly. At least with
+the devfs device names, (even though you can add your own naming
+scheme) some people will use the devfs-supplied names directly. This
+offends some people :-)
+
+Devfs is bloatware
+
+This is not even remotely true. As shown above,
+both code and data size are quite modest.
+
+
+How to report bugs
+
+If you have (or think you have) a bug with devfs, please follow the
+steps below:
+
+
+
+make sure you have enabled debugging output when configuring your
+kernel. You will need to set (at least) the following config options:
+
+CONFIG_DEVFS_DEBUG=y
+CONFIG_DEBUG_KERNEL=y
+CONFIG_DEBUG_SLAB=y
+
+
+
+please make sure you have the latest devfs patches applied. The
+latest kernel version might not have the latest devfs patches applied
+yet (Linus is very busy)
+
+
+save a copy of your complete kernel logs (preferably by
+using the dmesg programme) for later inclusion in your bug
+report. You may need to use the -s switch to increase the
+internal buffer size so you can capture all the boot messages.
+Don't edit or trim the dmesg output
+
+
+
+
+try booting with devfs=dall passed to the kernel boot