target/linux/generic/files/drivers/mtd/mtdsplit/mtdsplit_minor.c

   1 /*
   2  *  MTD splitter for MikroTik NOR devices
   3  *
   4  *  Copyright (C) 2017 Thibaut VARENE <varenet@parisc-linux.org>
   5  *
   6  *  This program is free software; you can redistribute it and/or modify it
   7  *  under the terms of the GNU General Public License version 2 as published
   8  *  by the Free Software Foundation.
   9  *
  10  *  The rootfs is expected at erase-block boundary due to the use of
  11  *  mtd_find_rootfs_from(). We use a trimmed down version of the yaffs header
  12  *  for two main reasons:
  13  *  - the original header uses weakly defined types (int, enum...) which can
  14  *    vary in length depending on build host (and the struct is not packed),
  15  *    and the name field can have a different total length depending on
  16  *    whether or not the yaffs code was _built_ with unicode support.
  17  *  - the only field that could be of real use here (file_size_low) contains
  18  *    invalid data in the header generated by kernel2minor, so we cannot use
  19  *    it to infer the exact position of the rootfs and do away with
  20  *    mtd_find_rootfs_from() (and thus have non-EB-aligned rootfs).
  21  */
  22
  23 #include <linux/module.h>
  24 #include <linux/init.h>
  25 #include <linux/kernel.h>
  26 #include <linux/slab.h>
  27 #include <linux/mtd/mtd.h>
  28 #include <linux/mtd/partitions.h>
  29 #include <linux/string.h>
  30 #include <linux/of.h>
  31
  32 #include "mtdsplit.h"
  33
  34 #define YAFFS_OBJECT_TYPE_FILE  0x1
  35 #define YAFFS_OBJECTID_ROOT     0x1
  36 #define YAFFS_SUM_UNUSED        0xFFFF
  37 #define YAFFS_NAME              "kernel"
  38
  39 #define MINOR_NR_PARTS          2
  40
  41 /*
  42  * This structure is based on yaffs_obj_hdr from yaffs_guts.h
  43  * The weak types match upstream. The fields have cpu-endianness
  44  */
  45 struct minor_header {
  46         int yaffs_type;
  47         int yaffs_obj_id;
  48         u16 yaffs_sum_unused;
  49         char yaffs_name[sizeof(YAFFS_NAME)];
  50 };
  51
  52 static int mtdsplit_parse_minor(struct mtd_info *master,
  53                                 const struct mtd_partition **pparts,
  54                                 struct mtd_part_parser_data *data)
  55 {
  56         struct minor_header hdr;
  57         size_t hdr_len, retlen;
  58         size_t rootfs_offset;
  59         struct mtd_partition *parts;
  60         int err;
  61
  62         hdr_len = sizeof(hdr);
  63         err = mtd_read(master, 0, hdr_len, &retlen, (void *) &hdr);
  64         if (err)
  65                 return err;
  66
  67         if (retlen != hdr_len)
  68                 return -EIO;
  69
  70         /* match header */
  71         if (hdr.yaffs_type != YAFFS_OBJECT_TYPE_FILE)
  72                 return -EINVAL;
  73
  74         if (hdr.yaffs_obj_id != YAFFS_OBJECTID_ROOT)
  75                 return -EINVAL;
  76
  77         if (hdr.yaffs_sum_unused != YAFFS_SUM_UNUSED)
  78                 return -EINVAL;
  79
  80         if (memcmp(hdr.yaffs_name, YAFFS_NAME, sizeof(YAFFS_NAME)))
  81                 return -EINVAL;
  82
  83         err = mtd_find_rootfs_from(master, master->erasesize, master->size,
  84                                    &rootfs_offset, NULL);
  85         if (err)
  86                 return err;
  87
  88         parts = kzalloc(MINOR_NR_PARTS * sizeof(*parts), GFP_KERNEL);
  89         if (!parts)
  90                 return -ENOMEM;
  91
  92         parts[0].name = KERNEL_PART_NAME;
  93         parts[0].offset = 0;
  94         parts[0].size = rootfs_offset;
  95
  96         parts[1].name = ROOTFS_PART_NAME;
  97         parts[1].offset = rootfs_offset;
  98         parts[1].size = master->size - rootfs_offset;
  99
 100         *pparts = parts;
 101         return MINOR_NR_PARTS;
 102 }
 103
 104 static const struct of_device_id mtdsplit_minor_of_match_table[] = {
 105         { .compatible = "mikrotik,minor" },
 106         {},
 107 };
 108 MODULE_DEVICE_TABLE(of, mtdsplit_minor_of_match_table);
 109
 110 static struct mtd_part_parser mtdsplit_minor_parser = {
 111         .owner = THIS_MODULE,
 112         .name = "minor-fw",
 113         .of_match_table = mtdsplit_minor_of_match_table,
 114         .parse_fn = mtdsplit_parse_minor,
 115         .type = MTD_PARSER_TYPE_FIRMWARE,
 116 };
 117
 118 static int __init mtdsplit_minor_init(void)
 119 {
 120         register_mtd_parser(&mtdsplit_minor_parser);
 121
 122         return 0;
 123 }
 124
 125 subsys_initcall(mtdsplit_minor_init);