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
  31 #include "mtdsplit.h"
  32
  33 #define YAFFS_OBJECT_TYPE_FILE  0x1
  34 #define YAFFS_OBJECTID_ROOT     0x1
  35 #define YAFFS_SUM_UNUSED        0xFFFF
  36 #define YAFFS_NAME              "kernel"
  37
  38 #define MINOR_NR_PARTS          2
  39
  40 /*
  41  * This structure is based on yaffs_obj_hdr from yaffs_guts.h
  42  * The weak types match upstream. The fields have cpu-endianness
  43  */
  44 struct minor_header {
  45         int yaffs_type;
  46         int yaffs_obj_id;
  47         u16 yaffs_sum_unused;
  48         char yaffs_name[sizeof(YAFFS_NAME)];
  49 };
  50
  51 static int mtdsplit_parse_minor(struct mtd_info *master,
  52                                 const struct mtd_partition **pparts,
  53                                 struct mtd_part_parser_data *data)
  54 {
  55         struct minor_header hdr;
  56         size_t hdr_len, retlen;
  57         size_t rootfs_offset;
  58         struct mtd_partition *parts;
  59         int err;
  60
  61         hdr_len = sizeof(hdr);
  62         err = mtd_read(master, 0, hdr_len, &retlen, (void *) &hdr);
  63         if (err)
  64                 return err;
  65
  66         if (retlen != hdr_len)
  67                 return -EIO;
  68
  69         /* match header */
  70         if (hdr.yaffs_type != YAFFS_OBJECT_TYPE_FILE)
  71                 return -EINVAL;
  72
  73         if (hdr.yaffs_obj_id != YAFFS_OBJECTID_ROOT)
  74                 return -EINVAL;
  75
  76         if (hdr.yaffs_sum_unused != YAFFS_SUM_UNUSED)
  77                 return -EINVAL;
  78
  79         if (memcmp(hdr.yaffs_name, YAFFS_NAME, sizeof(YAFFS_NAME)))
  80                 return -EINVAL;
  81
  82         err = mtd_find_rootfs_from(master, master->erasesize, master->size,
  83                                    &rootfs_offset, NULL);
  84         if (err)
  85                 return err;
  86
  87         parts = kzalloc(MINOR_NR_PARTS * sizeof(*parts), GFP_KERNEL);
  88         if (!parts)
  89                 return -ENOMEM;
  90
  91         parts[0].name = KERNEL_PART_NAME;
  92         parts[0].offset = 0;
  93         parts[0].size = rootfs_offset;
  94
  95         parts[1].name = ROOTFS_PART_NAME;
  96         parts[1].offset = rootfs_offset;
  97         parts[1].size = master->size - rootfs_offset;
  98
  99         *pparts = parts;
 100         return MINOR_NR_PARTS;
 101 }
 102
 103 static const struct of_device_id mtdsplit_minor_of_match_table[] = {
 104         { .compatible = "mikrotik,minor" },
 105         {},
 106 };
 107 MODULE_DEVICE_TABLE(of, mtdsplit_minor_of_match_table);
 108
 109 static struct mtd_part_parser mtdsplit_minor_parser = {
 110         .owner = THIS_MODULE,
 111         .name = "minor-fw",
 112         .of_match_table = mtdsplit_minor_of_match_table,
 113         .parse_fn = mtdsplit_parse_minor,
 114         .type = MTD_PARSER_TYPE_FIRMWARE,
 115 };
 116
 117 static int __init mtdsplit_minor_init(void)
 118 {
 119         register_mtd_parser(&mtdsplit_minor_parser);
 120
 121         return 0;
 122 }
 123
 124 subsys_initcall(mtdsplit_minor_init);