OpenWrt – Rev 3

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/*
 *  MTD splitter for MikroTik NOR devices
 *
 *  Copyright (C) 2017 Thibaut VARENE <varenet@parisc-linux.org>
 *
 *  This program is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU General Public License version 2 as published
 *  by the Free Software Foundation.
 *
 *  The rootfs is expected at erase-block boundary due to the use of
 *  mtd_find_rootfs_from(). We use a trimmed down version of the yaffs header
 *  for two main reasons:
 *  - the original header uses weakly defined types (int, enum...) which can
 *    vary in length depending on build host (and the struct is not packed),
 *    and the name field can have a different total length depending on
 *    whether or not the yaffs code was _built_ with unicode support.
 *  - the only field that could be of real use here (file_size_low) contains
 *    invalid data in the header generated by kernel2minor, so we cannot use
 *    it to infer the exact position of the rootfs and do away with
 *    mtd_find_rootfs_from() (and thus have non-EB-aligned rootfs).
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/partitions.h>
#include <linux/string.h>

#include "mtdsplit.h"

#define YAFFS_OBJECT_TYPE_FILE  0x1
#define YAFFS_OBJECTID_ROOT     0x1
#define YAFFS_SUM_UNUSED        0xFFFF
#define YAFFS_NAME              "kernel"

#define MINOR_NR_PARTS          2

/*
 * This structure is based on yaffs_obj_hdr from yaffs_guts.h
 * The weak types match upstream. The fields have cpu-endianness
 */
struct minor_header {
        int yaffs_type;
        int yaffs_obj_id;
        u16 yaffs_sum_unused;
        char yaffs_name[sizeof(YAFFS_NAME)];
};

static int mtdsplit_parse_minor(struct mtd_info *master,
                                const struct mtd_partition **pparts,
                                struct mtd_part_parser_data *data)
{
        struct minor_header hdr;
        size_t hdr_len, retlen;
        size_t rootfs_offset;
        struct mtd_partition *parts;
        int err;

        hdr_len = sizeof(hdr);
        err = mtd_read(master, 0, hdr_len, &retlen, (void *) &hdr);
        if (err)
                return err;

        if (retlen != hdr_len)
                return -EIO;

        /* match header */
        if (hdr.yaffs_type != YAFFS_OBJECT_TYPE_FILE)
                return -EINVAL;

        if (hdr.yaffs_obj_id != YAFFS_OBJECTID_ROOT)
                return -EINVAL;

        if (hdr.yaffs_sum_unused != YAFFS_SUM_UNUSED)
                return -EINVAL;

        if (memcmp(hdr.yaffs_name, YAFFS_NAME, sizeof(YAFFS_NAME)))
                return -EINVAL;

        err = mtd_find_rootfs_from(master, master->erasesize, master->size,
                                   &rootfs_offset, NULL);
        if (err)
                return err;

        parts = kzalloc(MINOR_NR_PARTS * sizeof(*parts), GFP_KERNEL);
        if (!parts)
                return -ENOMEM;

        parts[0].name = KERNEL_PART_NAME;
        parts[0].offset = 0;
        parts[0].size = rootfs_offset;

        parts[1].name = ROOTFS_PART_NAME;
        parts[1].offset = rootfs_offset;
        parts[1].size = master->size - rootfs_offset;

        *pparts = parts;
        return MINOR_NR_PARTS;
}

static struct mtd_part_parser mtdsplit_minor_parser = {
        .owner = THIS_MODULE,
        .name = "minor-fw",
        .parse_fn = mtdsplit_parse_minor,
        .type = MTD_PARSER_TYPE_FIRMWARE,
};

static int __init mtdsplit_minor_init(void)
{
        register_mtd_parser(&mtdsplit_minor_parser);

        return 0;
}

subsys_initcall(mtdsplit_minor_init);