由于自已经编译出来的16M版本的系统在安装软件的时候出现了很多的问题：更新配置或者安装软件的时候总是报签名有问题。无奈之下，决定安装官方的版本： https://downloads.openwrt.org/chaos_calmer/15.05/ar71xx/generic/openwrt-15.05-ar71xx-generic-tl-wr841n-v9-squashfs-factory.bin。心里想着应该可以正常开机吧，可惜了我那16M的flash。

怀着忐忑的心情，开始了第一次的开机。。。

一切都很顺利，kernel log中没有发现异常信息，串口终端也可以正常使用。用df命令查看一下flash的可用空间，奇迹发生了：

root@OpenWrt-wr802n-v1:~# df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                   12.6M      3.2M      9.4M  25% /
/dev/root                 2.3M      2.3M         0 100% /rom
tmpfs                    14.0M      1.2M     12.8M   9% /tmp
/dev/mtdblock3           12.6M      3.2M      9.4M  25% /overlay
overlayfs:/overlay       12.6M      3.2M      9.4M  25% /
tmpfs                   512.0K         0    512.0K   0% /dev

看到了吧，16M的flash可以正常被识别，再看看kernel log:

[    0.680000] m25p80 spi0.0: found w25q128, expected m25p80
[    0.690000] m25p80 spi0.0: w25q128 (16384 Kbytes)
[    0.690000] 5 tp-link partitions found on MTD device spi0.0
[    0.700000] Creating 5 MTD partitions on "spi0.0":
[    0.700000] 0x000000000000-0x000000020000 : "u-boot"
[    0.710000] 0x000000020000-0x00000012c55c : "kernel"
[    0.720000] 0x00000012c55c-0x000000ff0000 : "rootfs"
[    0.720000] mtd: device 2 (rootfs) set to be root filesystem
[    0.730000] 1 squashfs-split partitions found on MTD device rootfs
[    0.740000] 0x000000350000-0x000000ff0000 : "rootfs_data"
[    0.740000] 0x000000ff0000-0x000001000000 : "art"
[    0.750000] 0x000000020000-0x000000ff0000 : "firmware"

貌似已经被识别出来了， rootfs_data是什么？这是怎么做到的？

• 分区表是如何创建的

本能地去查看这个文件： https://dev.openwrt.org/browser/trunk/target/linux/ar71xx/files/arch/mips/ath79/mach-tl-wr841n-v9.c

#include "common.h"
#include "dev-eth.h"
#include "dev-gpio-buttons.h"
#include "dev-leds-gpio.h"
#include "dev-m25p80.h"
#include "dev-wmac.h"
#include "machtypes.h"

#define TL_WR841NV9_GPIO_LED_WLAN	13
#define TL_WR841NV9_GPIO_LED_QSS	3
#define TL_WR841NV9_GPIO_LED_WAN	4
#define TL_WR841NV9_GPIO_LED_LAN1	16
#define TL_WR841NV9_GPIO_LED_LAN2	15
#define TL_WR841NV9_GPIO_LED_LAN3	14
#define TL_WR841NV9_GPIO_LED_LAN4	11

#define TL_WR841NV9_GPIO_BTN_RESET	12
#define TL_WR841NV9_GPIO_BTN_WIFI	17

#define TL_WR841NV9_KEYS_POLL_INTERVAL	20	/* msecs */
#define TL_WR841NV9_KEYS_DEBOUNCE_INTERVAL (3 * TL_WR841NV9_KEYS_POLL_INTERVAL)

static const char *tl_wr841n_v9_part_probes[] = {
	"tp-link",
	NULL,
};

static struct flash_platform_data tl_wr841n_v9_flash_data = {
	.part_probes	= tl_wr841n_v9_part_probes,
};

static struct gpio_led tl_wr841n_v9_leds_gpio[] __initdata = {
	{
		.name		= "tp-link:green:lan1",
		.gpio		= TL_WR841NV9_GPIO_LED_LAN1,
		.active_low	= 1,
	}, {
		.name		= "tp-link:green:lan2",
		.gpio		= TL_WR841NV9_GPIO_LED_LAN2,
		.active_low	= 1,
	}, {
		.name		= "tp-link:green:lan3",
		.gpio		= TL_WR841NV9_GPIO_LED_LAN3,
		.active_low	= 1,
	}, {
		.name		= "tp-link:green:lan4",
		.gpio		= TL_WR841NV9_GPIO_LED_LAN4,
		.active_low	= 1,
	}, {
		.name		= "tp-link:green:qss",
		.gpio		= TL_WR841NV9_GPIO_LED_QSS,
		.active_low	= 1,
	}, {
		.name		= "tp-link:green:wan",
		.gpio		= TL_WR841NV9_GPIO_LED_WAN,
		.active_low	= 1,
	}, {
		.name		= "tp-link:green:wlan",
		.gpio		= TL_WR841NV9_GPIO_LED_WLAN,
		.active_low	= 1,
	},
};

static struct gpio_keys_button tl_wr841n_v9_gpio_keys[] __initdata = {
	{
		.desc		= "Reset button",
		.type		= EV_KEY,
		.code		= KEY_RESTART,
		.debounce_interval = TL_WR841NV9_KEYS_DEBOUNCE_INTERVAL,
		.gpio		= TL_WR841NV9_GPIO_BTN_RESET,
		.active_low	= 1,
	}, {
		.desc		= "WIFI button",
		.type		= EV_KEY,
		.code		= KEY_RFKILL,
		.debounce_interval = TL_WR841NV9_KEYS_DEBOUNCE_INTERVAL,
		.gpio		= TL_WR841NV9_GPIO_BTN_WIFI,
		.active_low	= 1,
	}
};


static void __init tl_ap143_setup(void)
{
	u8 *mac = (u8 *) KSEG1ADDR(0x1f01fc00);
	u8 *ee = (u8 *) KSEG1ADDR(0x1fff1000);
	u8 tmpmac[ETH_ALEN];

	ath79_register_m25p80(&tl_wr841n_v9_flash_data);

	ath79_setup_ar933x_phy4_switch(false, false);

	ath79_register_mdio(0, 0x0);

	/* LAN */
	ath79_eth1_data.phy_if_mode = PHY_INTERFACE_MODE_GMII;
	ath79_eth1_data.duplex = DUPLEX_FULL;
	ath79_switch_data.phy_poll_mask |= BIT(4);
	ath79_init_mac(ath79_eth1_data.mac_addr, mac, 0);
	ath79_register_eth(1);

	/* WAN */
	ath79_switch_data.phy4_mii_en = 1;
	ath79_eth0_data.phy_if_mode = PHY_INTERFACE_MODE_MII;
	ath79_eth0_data.duplex = DUPLEX_FULL;
	ath79_eth0_data.speed = SPEED_100;
	ath79_eth0_data.phy_mask = BIT(4);
	ath79_init_mac(ath79_eth0_data.mac_addr, mac, 1);
	ath79_register_eth(0);

	ath79_init_mac(tmpmac, mac, 0);
	ath79_register_wmac(ee, tmpmac);
}

static void __init tl_wr841n_v9_setup(void)
{
	tl_ap143_setup();

	ath79_register_leds_gpio(-1, ARRAY_SIZE(tl_wr841n_v9_leds_gpio),
				 tl_wr841n_v9_leds_gpio);

	ath79_register_gpio_keys_polled(1, TL_WR841NV9_KEYS_POLL_INTERVAL,
					ARRAY_SIZE(tl_wr841n_v9_gpio_keys),
					tl_wr841n_v9_gpio_keys);
}

MIPS_MACHINE(ATH79_MACH_TL_WR841N_V9, "TL-WR841N-v9", "TP-LINK TL-WR841N/ND v9",
	     tl_wr841n_v9_setup);

tl_wr841n_v9_part_probes中的”tp-link”是什么？

于是乎又找到了这个文件：https://dev.openwrt.org/browser/trunk/target/linux/ar71xx/files/drivers/mtd/tplinkpart.c

/*
 * Copyright (C) 2011 Gabor Juhos <juhosg@openwrt.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.
 *
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/magic.h>

#include <linux/mtd/mtd.h>
#include <linux/mtd/partitions.h>

#define TPLINK_NUM_PARTS	5
#define TPLINK_HEADER_V1	0x01000000
#define TPLINK_HEADER_V2	0x02000000
#define MD5SUM_LEN		16

#define TPLINK_ART_LEN		0x10000
#define TPLINK_KERNEL_OFFS	0x20000
#define TPLINK_64K_KERNEL_OFFS	0x10000

struct tplink_fw_header {
	uint32_t	version;	/* header version */
	char		vendor_name[24];
	char		fw_version[36];
	uint32_t	hw_id;		/* hardware id */
	uint32_t	hw_rev;		/* hardware revision */
	uint32_t	unk1;
	uint8_t		md5sum1[MD5SUM_LEN];
	uint32_t	unk2;
	uint8_t		md5sum2[MD5SUM_LEN];
	uint32_t	unk3;
	uint32_t	kernel_la;	/* kernel load address */
	uint32_t	kernel_ep;	/* kernel entry point */
	uint32_t	fw_length;	/* total length of the firmware */
	uint32_t	kernel_ofs;	/* kernel data offset */
	uint32_t	kernel_len;	/* kernel data length */
	uint32_t	rootfs_ofs;	/* rootfs data offset */
	uint32_t	rootfs_len;	/* rootfs data length */
	uint32_t	boot_ofs;	/* bootloader data offset */
	uint32_t	boot_len;	/* bootloader data length */
	uint8_t		pad[360];
} __attribute__ ((packed));

static struct tplink_fw_header *
tplink_read_header(struct mtd_info *mtd, size_t offset)
{
	struct tplink_fw_header *header;
	size_t header_len;
	size_t retlen;
	int ret;
	u32 t;

	header = vmalloc(sizeof(*header));
	if (!header)
		goto err;

	header_len = sizeof(struct tplink_fw_header);
	ret = mtd_read(mtd, offset, header_len, &retlen,
		       (unsigned char *) header);
	if (ret)
		goto err_free_header;

	if (retlen != header_len)
		goto err_free_header;

	/* sanity checks */
	t = be32_to_cpu(header->version);
	if ((t != TPLINK_HEADER_V1) && (t != TPLINK_HEADER_V2))
		goto err_free_header;

	t = be32_to_cpu(header->kernel_ofs);
	if (t != header_len)
		goto err_free_header;

	return header;

err_free_header:
	vfree(header);
err:
	return NULL;
}

static int tplink_check_rootfs_magic(struct mtd_info *mtd, size_t offset)
{
	u32 magic;
	size_t retlen;
	int ret;

	ret = mtd_read(mtd, offset, sizeof(magic), &retlen,
		       (unsigned char *) &magic);
	if (ret)
		return ret;

	if (retlen != sizeof(magic))
		return -EIO;

	if (le32_to_cpu(magic) != SQUASHFS_MAGIC &&
	    magic != 0x19852003)
		return -EINVAL;

	return 0;
}

static int tplink_parse_partitions_offset(struct mtd_info *master,
				   struct mtd_partition **pparts,
				   struct mtd_part_parser_data *data,
				   size_t offset)
{
	struct mtd_partition *parts;
	struct tplink_fw_header *header;
	int nr_parts;
	size_t art_offset;
	size_t rootfs_offset;
	size_t squashfs_offset;
	int ret;

	nr_parts = TPLINK_NUM_PARTS;
	parts = kzalloc(nr_parts * sizeof(struct mtd_partition), GFP_KERNEL);
	if (!parts) {
		ret = -ENOMEM;
		goto err;
	}

	header = tplink_read_header(master, offset);
	if (!header) {
		pr_notice("%s: no TP-Link header found\n", master->name);
		ret = -ENODEV;
		goto err_free_parts;
	}

	squashfs_offset = offset + sizeof(struct tplink_fw_header) +
			  be32_to_cpu(header->kernel_len);

	ret = tplink_check_rootfs_magic(master, squashfs_offset);
	if (ret == 0)
		rootfs_offset = squashfs_offset;
	else
		rootfs_offset = offset + be32_to_cpu(header->rootfs_ofs);

	art_offset = master->size - TPLINK_ART_LEN;

	parts[0].name = "u-boot";
	parts[0].offset = 0;
	parts[0].size = offset;
	parts[0].mask_flags = MTD_WRITEABLE;

	parts[1].name = "kernel";
	parts[1].offset = offset;
	parts[1].size = rootfs_offset - offset;

	parts[2].name = "rootfs";
	parts[2].offset = rootfs_offset;
	parts[2].size = art_offset - rootfs_offset;

	parts[3].name = "art";
	parts[3].offset = art_offset;
	parts[3].size = TPLINK_ART_LEN;
	parts[3].mask_flags = MTD_WRITEABLE;

	parts[4].name = "firmware";
	parts[4].offset = offset;
	parts[4].size = art_offset - offset;

	vfree(header);

	*pparts = parts;
	return nr_parts;

err_free_parts:
	kfree(parts);
err:
	*pparts = NULL;
	return ret;
}

static int tplink_parse_partitions(struct mtd_info *master,
				   struct mtd_partition **pparts,
				   struct mtd_part_parser_data *data)
{
	return tplink_parse_partitions_offset(master, pparts, data,
		                              TPLINK_KERNEL_OFFS);
}

static int tplink_parse_64k_partitions(struct mtd_info *master,
				   struct mtd_partition **pparts,
				   struct mtd_part_parser_data *data)
{
	return tplink_parse_partitions_offset(master, pparts, data,
		                              TPLINK_64K_KERNEL_OFFS);
}

static struct mtd_part_parser tplink_parser = {
	.owner		= THIS_MODULE,
	.parse_fn	= tplink_parse_partitions,
	.name		= "tp-link",
};

static struct mtd_part_parser tplink_64k_parser = {
	.owner		= THIS_MODULE,
	.parse_fn	= tplink_parse_64k_partitions,
	.name		= "tp-link-64k",
};

static int __init tplink_parser_init(void)
{
	register_mtd_parser(&tplink_parser);
	register_mtd_parser(&tplink_64k_parser);

	return 0;
}

module_init(tplink_parser_init);

MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Gabor Juhos <juhosg@openwrt.org>");

分区表原来是这么来的，于是了然了。

• rootfs_data分区又是怎么回事呢

首先看一下flash的布局：

Layer0	raw flash(w25q128), 16384KB
Layer1	mtd0 u-boot(tuboot.bin) 128KB		mtd5 firmware 16192KB=16384-(128+64)			mtd4 art 64KB
Layer2			mtd1 kernel 大约1MB	mtd2 rootfs
Layer3				/dev/root 大约2.3MB	mtd3 rootfs_data 大约12.6MB

很显然/dev/root就是根文件系统了，而mtd2什么时候被分成了两个部分了呢？

先贴一下代码（OpenWrt 15.05

build_dir/target-mips_34kc_uClibc-0.9.33.2/linux-ar71xx_generic/linux-3.18.23/drivers/mtd/mtdpart.c)：

/*
 * Simple MTD partitioning layer
 *
 * Copyright © 2000 Nicolas Pitre <nico@fluxnic.net>
 * Copyright © 2002 Thomas Gleixner <gleixner@linutronix.de>
 * Copyright © 2000-2010 David Woodhouse <dwmw2@infradead.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/kmod.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/partitions.h>
#include <linux/magic.h>
#include <linux/err.h>

#include "mtdcore.h"
#include "mtdsplit/mtdsplit.h"

#define MTD_ERASE_PARTIAL	0x8000 /* partition only covers parts of an erase block */

/* Our partition linked list */
static LIST_HEAD(mtd_partitions);
static DEFINE_MUTEX(mtd_partitions_mutex);

/* Our partition node structure */
struct mtd_part {
	struct mtd_info mtd;
	struct mtd_info *master;
	uint64_t offset;
	struct list_head list;
};

static void mtd_partition_split(struct mtd_info *master, struct mtd_part *part);

/*
 * Given a pointer to the MTD object in the mtd_part structure, we can retrieve
 * the pointer to that structure with this macro.
 */
#define PART(x)  ((struct mtd_part *)(x))

/*
 * MTD methods which simply translate the effective address and pass through
 * to the _real_ device.
 */

static int part_read(struct mtd_info *mtd, loff_t from, size_t len,
		size_t *retlen, u_char *buf)
{
	struct mtd_part *part = PART(mtd);
	struct mtd_ecc_stats stats;
	int res;

	stats = part->master->ecc_stats;
	res = part->master->_read(part->master, from + part->offset, len,
				  retlen, buf);
	if (unlikely(mtd_is_eccerr(res)))
		mtd->ecc_stats.failed +=
			part->master->ecc_stats.failed - stats.failed;
	else
		mtd->ecc_stats.corrected +=
			part->master->ecc_stats.corrected - stats.corrected;
	return res;
}

static int part_point(struct mtd_info *mtd, loff_t from, size_t len,
		size_t *retlen, void **virt, resource_size_t *phys)
{
	struct mtd_part *part = PART(mtd);

	return part->master->_point(part->master, from + part->offset, len,
				    retlen, virt, phys);
}

static int part_unpoint(struct mtd_info *mtd, loff_t from, size_t len)
{
	struct mtd_part *part = PART(mtd);

	return part->master->_unpoint(part->master, from + part->offset, len);
}

static unsigned long part_get_unmapped_area(struct mtd_info *mtd,
					    unsigned long len,
					    unsigned long offset,
					    unsigned long flags)
{
	struct mtd_part *part = PART(mtd);

	offset += part->offset;
	return part->master->_get_unmapped_area(part->master, len, offset,
						flags);
}

static int part_read_oob(struct mtd_info *mtd, loff_t from,
		struct mtd_oob_ops *ops)
{
	struct mtd_part *part = PART(mtd);
	int res;

	if (from >= mtd->size)
		return -EINVAL;
	if (ops->datbuf && from + ops->len > mtd->size)
		return -EINVAL;

	/*
	 * If OOB is also requested, make sure that we do not read past the end
	 * of this partition.
	 */
	if (ops->oobbuf) {
		size_t len, pages;

		if (ops->mode == MTD_OPS_AUTO_OOB)
			len = mtd->oobavail;
		else
			len = mtd->oobsize;
		pages = mtd_div_by_ws(mtd->size, mtd);
		pages -= mtd_div_by_ws(from, mtd);
		if (ops->ooboffs + ops->ooblen > pages * len)
			return -EINVAL;
	}

	res = part->master->_read_oob(part->master, from + part->offset, ops);
	if (unlikely(res)) {
		if (mtd_is_bitflip(res))
			mtd->ecc_stats.corrected++;
		if (mtd_is_eccerr(res))
			mtd->ecc_stats.failed++;
	}
	return res;
}

static int part_read_user_prot_reg(struct mtd_info *mtd, loff_t from,
		size_t len, size_t *retlen, u_char *buf)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_read_user_prot_reg(part->master, from, len,
						 retlen, buf);
}

static int part_get_user_prot_info(struct mtd_info *mtd, size_t len,
				   size_t *retlen, struct otp_info *buf)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_get_user_prot_info(part->master, len, retlen,
						 buf);
}

static int part_read_fact_prot_reg(struct mtd_info *mtd, loff_t from,
		size_t len, size_t *retlen, u_char *buf)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_read_fact_prot_reg(part->master, from, len,
						 retlen, buf);
}

static int part_get_fact_prot_info(struct mtd_info *mtd, size_t len,
				   size_t *retlen, struct otp_info *buf)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_get_fact_prot_info(part->master, len, retlen,
						 buf);
}

static int part_write(struct mtd_info *mtd, loff_t to, size_t len,
		size_t *retlen, const u_char *buf)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_write(part->master, to + part->offset, len,
				    retlen, buf);
}

static int part_panic_write(struct mtd_info *mtd, loff_t to, size_t len,
		size_t *retlen, const u_char *buf)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_panic_write(part->master, to + part->offset, len,
					  retlen, buf);
}

static int part_write_oob(struct mtd_info *mtd, loff_t to,
		struct mtd_oob_ops *ops)
{
	struct mtd_part *part = PART(mtd);

	if (to >= mtd->size)
		return -EINVAL;
	if (ops->datbuf && to + ops->len > mtd->size)
		return -EINVAL;
	return part->master->_write_oob(part->master, to + part->offset, ops);
}

static int part_write_user_prot_reg(struct mtd_info *mtd, loff_t from,
		size_t len, size_t *retlen, u_char *buf)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_write_user_prot_reg(part->master, from, len,
						  retlen, buf);
}

static int part_lock_user_prot_reg(struct mtd_info *mtd, loff_t from,
		size_t len)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_lock_user_prot_reg(part->master, from, len);
}

static int part_writev(struct mtd_info *mtd, const struct kvec *vecs,
		unsigned long count, loff_t to, size_t *retlen)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_writev(part->master, vecs, count,
				     to + part->offset, retlen);
}

static int part_erase(struct mtd_info *mtd, struct erase_info *instr)
{
	struct mtd_part *part = PART(mtd);
	int ret;


	instr->partial_start = false;
	if (mtd->flags & MTD_ERASE_PARTIAL) {
		size_t readlen = 0;
		u64 mtd_ofs;

		instr->erase_buf = kmalloc(part->master->erasesize, GFP_ATOMIC);
		if (!instr->erase_buf)
			return -ENOMEM;

		mtd_ofs = part->offset + instr->addr;
		instr->erase_buf_ofs = do_div(mtd_ofs, part->master->erasesize);

		if (instr->erase_buf_ofs > 0) {
			instr->addr -= instr->erase_buf_ofs;
			ret = mtd_read(part->master,
				instr->addr + part->offset,
				part->master->erasesize,
				&readlen, instr->erase_buf);

			instr->len += instr->erase_buf_ofs;
			instr->partial_start = true;
		} else {
			mtd_ofs = part->offset + part->mtd.size;
			instr->erase_buf_ofs = part->master->erasesize -
				do_div(mtd_ofs, part->master->erasesize);

			if (instr->erase_buf_ofs > 0) {
				instr->len += instr->erase_buf_ofs;
				ret = mtd_read(part->master,
					part->offset + instr->addr +
					instr->len - part->master->erasesize,
					part->master->erasesize, &readlen,
					instr->erase_buf);
			} else {
				ret = 0;
			}
		}
		if (ret < 0) {
			kfree(instr->erase_buf);
			return ret;
		}

	}

	instr->addr += part->offset;
	ret = part->master->_erase(part->master, instr);
	if (ret) {
		if (instr->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
			instr->fail_addr -= part->offset;
		instr->addr -= part->offset;
		if (mtd->flags & MTD_ERASE_PARTIAL)
			kfree(instr->erase_buf);
	}

	return ret;
}

void mtd_erase_callback(struct erase_info *instr)
{
	if (instr->mtd->_erase == part_erase) {
		struct mtd_part *part = PART(instr->mtd);
		size_t wrlen = 0;

		if (instr->mtd->flags & MTD_ERASE_PARTIAL) {
			if (instr->partial_start) {
				part->master->_write(part->master,
					instr->addr, instr->erase_buf_ofs,
					&wrlen, instr->erase_buf);
				instr->addr += instr->erase_buf_ofs;
			} else {
				instr->len -= instr->erase_buf_ofs;
				part->master->_write(part->master,
					instr->addr + instr->len,
					instr->erase_buf_ofs, &wrlen,
					instr->erase_buf +
					part->master->erasesize -
					instr->erase_buf_ofs);
			}
			kfree(instr->erase_buf);
		}
		if (instr->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
			instr->fail_addr -= part->offset;
		instr->addr -= part->offset;
	}
	if (instr->callback)
		instr->callback(instr);
}
EXPORT_SYMBOL_GPL(mtd_erase_callback);

static int part_lock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_lock(part->master, ofs + part->offset, len);
}

static int part_unlock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
{
	struct mtd_part *part = PART(mtd);

	ofs += part->offset;
	if (mtd->flags & MTD_ERASE_PARTIAL) {
		/* round up len to next erasesize and round down offset to prev block */
		len = (mtd_div_by_eb(len, part->master) + 1) * part->master->erasesize;
		ofs &= ~(part->master->erasesize - 1);
	}
	return part->master->_unlock(part->master, ofs, len);
}

static int part_is_locked(struct mtd_info *mtd, loff_t ofs, uint64_t len)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_is_locked(part->master, ofs + part->offset, len);
}

static void part_sync(struct mtd_info *mtd)
{
	struct mtd_part *part = PART(mtd);
	part->master->_sync(part->master);
}

static int part_suspend(struct mtd_info *mtd)
{
	struct mtd_part *part = PART(mtd);
	return part->master->_suspend(part->master);
}

static void part_resume(struct mtd_info *mtd)
{
	struct mtd_part *part = PART(mtd);
	part->master->_resume(part->master);
}

static int part_block_isreserved(struct mtd_info *mtd, loff_t ofs)
{
	struct mtd_part *part = PART(mtd);
	ofs += part->offset;
	return part->master->_block_isreserved(part->master, ofs);
}

static int part_block_isbad(struct mtd_info *mtd, loff_t ofs)
{
	struct mtd_part *part = PART(mtd);
	ofs += part->offset;
	return part->master->_block_isbad(part->master, ofs);
}

static int part_block_markbad(struct mtd_info *mtd, loff_t ofs)
{
	struct mtd_part *part = PART(mtd);
	int res;

	ofs += part->offset;
	res = part->master->_block_markbad(part->master, ofs);
	if (!res)
		mtd->ecc_stats.badblocks++;
	return res;
}

static inline void free_partition(struct mtd_part *p)
{
	kfree(p->mtd.name);
	kfree(p);
}

/*
 * This function unregisters and destroy all slave MTD objects which are
 * attached to the given master MTD object.
 */

int del_mtd_partitions(struct mtd_info *master)
{
	struct mtd_part *slave, *next;
	int ret, err = 0;

	mutex_lock(&mtd_partitions_mutex);
	list_for_each_entry_safe(slave, next, &mtd_partitions, list)
		if (slave->master == master) {
			ret = del_mtd_device(&slave->mtd);
			if (ret < 0) {
				err = ret;
				continue;
			}
			list_del(&slave->list);
			free_partition(slave);
		}
	mutex_unlock(&mtd_partitions_mutex);

	return err;
}

static struct mtd_part *allocate_partition(struct mtd_info *master,
			const struct mtd_partition *part, int partno,
			uint64_t cur_offset)
{
	struct mtd_part *slave;
	char *name;

	/* allocate the partition structure */
	slave = kzalloc(sizeof(*slave), GFP_KERNEL);
	name = kstrdup(part->name, GFP_KERNEL);
	if (!name || !slave) {
		printk(KERN_ERR"memory allocation error while creating partitions for \"%s\"\n",
		       master->name);
		kfree(name);
		kfree(slave);
		return ERR_PTR(-ENOMEM);
	}

	/* set up the MTD object for this partition */
	slave->mtd.type = master->type;
	slave->mtd.flags = master->flags & ~part->mask_flags;
	slave->mtd.size = part->size;
	slave->mtd.writesize = master->writesize;
	slave->mtd.writebufsize = master->writebufsize;
	slave->mtd.oobsize = master->oobsize;
	slave->mtd.oobavail = master->oobavail;
	slave->mtd.subpage_sft = master->subpage_sft;

	slave->mtd.name = name;
	slave->mtd.owner = master->owner;
	slave->mtd.backing_dev_info = master->backing_dev_info;

	/* NOTE:  we don't arrange MTDs as a tree; it'd be error-prone
	 * to have the same data be in two different partitions.
	 */
	slave->mtd.dev.parent = master->dev.parent;

	slave->mtd._read = part_read;
	slave->mtd._write = part_write;

	if (master->_panic_write)
		slave->mtd._panic_write = part_panic_write;

	if (master->_point && master->_unpoint) {
		slave->mtd._point = part_point;
		slave->mtd._unpoint = part_unpoint;
	}

	if (master->_get_unmapped_area)
		slave->mtd._get_unmapped_area = part_get_unmapped_area;
	if (master->_read_oob)
		slave->mtd._read_oob = part_read_oob;
	if (master->_write_oob)
		slave->mtd._write_oob = part_write_oob;
	if (master->_read_user_prot_reg)
		slave->mtd._read_user_prot_reg = part_read_user_prot_reg;
	if (master->_read_fact_prot_reg)
		slave->mtd._read_fact_prot_reg = part_read_fact_prot_reg;
	if (master->_write_user_prot_reg)
		slave->mtd._write_user_prot_reg = part_write_user_prot_reg;
	if (master->_lock_user_prot_reg)
		slave->mtd._lock_user_prot_reg = part_lock_user_prot_reg;
	if (master->_get_user_prot_info)
		slave->mtd._get_user_prot_info = part_get_user_prot_info;
	if (master->_get_fact_prot_info)
		slave->mtd._get_fact_prot_info = part_get_fact_prot_info;
	if (master->_sync)
		slave->mtd._sync = part_sync;
	if (!partno && !master->dev.class && master->_suspend &&
	    master->_resume) {
			slave->mtd._suspend = part_suspend;
			slave->mtd._resume = part_resume;
	}
	if (master->_writev)
		slave->mtd._writev = part_writev;
	if (master->_lock)
		slave->mtd._lock = part_lock;
	if (master->_unlock)
		slave->mtd._unlock = part_unlock;
	if (master->_is_locked)
		slave->mtd._is_locked = part_is_locked;
	if (master->_block_isreserved)
		slave->mtd._block_isreserved = part_block_isreserved;
	if (master->_block_isbad)
		slave->mtd._block_isbad = part_block_isbad;
	if (master->_block_markbad)
		slave->mtd._block_markbad = part_block_markbad;
	slave->mtd._erase = part_erase;
	slave->master = master;
	slave->offset = part->offset;

	if (slave->offset == MTDPART_OFS_APPEND)
		slave->offset = cur_offset;
	if (slave->offset == MTDPART_OFS_NXTBLK) {
		/* Round up to next erasesize */
		slave->offset = mtd_roundup_to_eb(cur_offset, master);
		if (slave->offset != cur_offset)
			printk(KERN_NOTICE "Moving partition %d: "
			       "0x%012llx -> 0x%012llx\n", partno,
			       (unsigned long long)cur_offset, (unsigned long long)slave->offset);
	}
	if (slave->offset == MTDPART_OFS_RETAIN) {
		slave->offset = cur_offset;
		if (master->size - slave->offset >= slave->mtd.size) {
			slave->mtd.size = master->size - slave->offset
							- slave->mtd.size;
		} else {
			printk(KERN_ERR "mtd partition \"%s\" doesn't have enough space: %#llx < %#llx, disabled\n",
				part->name, master->size - slave->offset,
				slave->mtd.size);
			/* register to preserve ordering */
			goto out_register;
		}
	}
	if (slave->mtd.size == MTDPART_SIZ_FULL)
		slave->mtd.size = master->size - slave->offset;

	printk(KERN_NOTICE "0x%012llx-0x%012llx : \"%s\"\n", (unsigned long long)slave->offset,
		(unsigned long long)(slave->offset + slave->mtd.size), slave->mtd.name);

	/* let's do some sanity checks */
	if (slave->offset >= master->size) {
		/* let's register it anyway to preserve ordering */
		slave->offset = 0;
		slave->mtd.size = 0;
		printk(KERN_ERR"mtd: partition \"%s\" is out of reach -- disabled\n",
			part->name);
		goto out_register;
	}
	if (slave->offset + slave->mtd.size > master->size) {
		slave->mtd.size = master->size - slave->offset;
		printk(KERN_WARNING"mtd: partition \"%s\" extends beyond the end of device \"%s\" -- size truncated to %#llx\n",
			part->name, master->name, (unsigned long long)slave->mtd.size);
	}
	if (master->numeraseregions > 1) {
		/* Deal with variable erase size stuff */
		int i, max = master->numeraseregions;
		u64 end = slave->offset + slave->mtd.size;
		struct mtd_erase_region_info *regions = master->eraseregions;

		/* Find the first erase regions which is part of this
		 * partition. */
		for (i = 0; i < max && regions[i].offset <= slave->offset; i++)
			;
		/* The loop searched for the region _behind_ the first one */
		if (i > 0)
			i--;

		/* Pick biggest erasesize */
		for (; i < max && regions[i].offset < end; i++) {
			if (slave->mtd.erasesize < regions[i].erasesize) {
				slave->mtd.erasesize = regions[i].erasesize;
			}
		}
		BUG_ON(slave->mtd.erasesize == 0);
	} else {
		/* Single erase size */
		slave->mtd.erasesize = master->erasesize;
	}

	if ((slave->mtd.flags & MTD_WRITEABLE) &&
	    mtd_mod_by_eb(slave->offset, &slave->mtd)) {
		/* Doesn't start on a boundary of major erase size */
		slave->mtd.flags |= MTD_ERASE_PARTIAL;
		if (((u32) slave->mtd.size) > master->erasesize)
			slave->mtd.flags &= ~MTD_WRITEABLE;
		else
			slave->mtd.erasesize = slave->mtd.size;
	}
	if ((slave->mtd.flags & MTD_WRITEABLE) &&
	    mtd_mod_by_eb(slave->offset + slave->mtd.size, &slave->mtd)) {
		slave->mtd.flags |= MTD_ERASE_PARTIAL;

		if ((u32) slave->mtd.size > master->erasesize)
			slave->mtd.flags &= ~MTD_WRITEABLE;
		else
			slave->mtd.erasesize = slave->mtd.size;
	}

	slave->mtd.ecclayout = master->ecclayout;
	slave->mtd.ecc_step_size = master->ecc_step_size;
	slave->mtd.ecc_strength = master->ecc_strength;
	slave->mtd.bitflip_threshold = master->bitflip_threshold;

	if (master->_block_isbad) {
		uint64_t offs = 0;

		while (offs < slave->mtd.size) {
			if (mtd_block_isreserved(master, offs + slave->offset))
				slave->mtd.ecc_stats.bbtblocks++;
			else if (mtd_block_isbad(master, offs + slave->offset))
				slave->mtd.ecc_stats.badblocks++;
			offs += slave->mtd.erasesize;
		}
	}

out_register:
	return slave;
}


static int
__mtd_add_partition(struct mtd_info *master, const char *name,
		    long long offset, long long length, bool dup_check)
{
	struct mtd_partition part;
	struct mtd_part *p, *new;
	uint64_t start, end;
	int ret = 0;

	/* the direct offset is expected */
	if (offset == MTDPART_OFS_APPEND ||
	    offset == MTDPART_OFS_NXTBLK)
		return -EINVAL;

	if (length == MTDPART_SIZ_FULL)
		length = master->size - offset;

	if (length <= 0)
		return -EINVAL;

	part.name = name;
	part.size = length;
	part.offset = offset;
	part.mask_flags = 0;
	part.ecclayout = NULL;

	new = allocate_partition(master, &part, -1, offset);
	if (IS_ERR(new))
		return PTR_ERR(new);

	start = offset;
	end = offset + length;

	mutex_lock(&mtd_partitions_mutex);
	if (dup_check) {
		list_for_each_entry(p, &mtd_partitions, list)
			if (p->master == master) {
				if ((start >= p->offset) &&
				    (start < (p->offset + p->mtd.size)))
					goto err_inv;

				if ((end >= p->offset) &&
				    (end < (p->offset + p->mtd.size)))
					goto err_inv;
			}
	}

	list_add(&new->list, &mtd_partitions);
	mutex_unlock(&mtd_partitions_mutex);

	add_mtd_device(&new->mtd);
	mtd_partition_split(master, new);

	return ret;
err_inv:
	mutex_unlock(&mtd_partitions_mutex);
	free_partition(new);
	return -EINVAL;
}
EXPORT_SYMBOL_GPL(mtd_add_partition);

int mtd_add_partition(struct mtd_info *master, const char *name,
		      long long offset, long long length)
{
	return __mtd_add_partition(master, name, offset, length, true);
}

int mtd_del_partition(struct mtd_info *master, int partno)
{
	struct mtd_part *slave, *next;
	int ret = -EINVAL;

	mutex_lock(&mtd_partitions_mutex);
	list_for_each_entry_safe(slave, next, &mtd_partitions, list)
		if ((slave->master == master) &&
		    (slave->mtd.index == partno)) {
			ret = del_mtd_device(&slave->mtd);
			if (ret < 0)
				break;

			list_del(&slave->list);
			free_partition(slave);
			break;
		}
	mutex_unlock(&mtd_partitions_mutex);

	return ret;
}
EXPORT_SYMBOL_GPL(mtd_del_partition);

static int
run_parsers_by_type(struct mtd_part *slave, enum mtd_parser_type type)
{
	struct mtd_partition *parts;
	int nr_parts;
	int i;

	nr_parts = parse_mtd_partitions_by_type(&slave->mtd, type, &parts,
						NULL);
	if (nr_parts <= 0)
		return nr_parts;

	if (WARN_ON(!parts))
		return 0;

	for (i = 0; i < nr_parts; i++) {
		/* adjust partition offsets */
		parts[i].offset += slave->offset;

		__mtd_add_partition(slave->master,
				    parts[i].name,
				    parts[i].offset,
				    parts[i].size,
				    false);
	}

	kfree(parts);

	return nr_parts;
}

static inline unsigned long
mtd_pad_erasesize(struct mtd_info *mtd, int offset, int len)
{
	unsigned long mask = mtd->erasesize - 1;

	len += offset & mask;
	len = (len + mask) & ~mask;
	len -= offset & mask;
	return len;
}

static int split_squashfs(struct mtd_info *master, int offset, int *split_offset)
{
	size_t squashfs_len;
	int len, ret;

	ret = mtd_get_squashfs_len(master, offset, &squashfs_len);
	if (ret)
		return ret;

	len = mtd_pad_erasesize(master, offset, squashfs_len);
	*split_offset = offset + len;

	return 0;
}

static void split_rootfs_data(struct mtd_info *master, struct mtd_part *part)
{
	unsigned int split_offset = 0;
	unsigned int split_size;
	int ret;

	ret = split_squashfs(master, part->offset, &split_offset);
	if (ret)
		return;

	if (split_offset <= 0)
		return;

	if (config_enabled(CONFIG_MTD_SPLIT_SQUASHFS_ROOT))
		pr_err("Dedicated partitioner didn't create \"rootfs_data\" partition, please fill a bug report!\n");
	else
		pr_warn("Support for built-in \"rootfs_data\" splitter will be removed, please use CONFIG_MTD_SPLIT_SQUASHFS_ROOT\n");

	split_size = part->mtd.size - (split_offset - part->offset);
	printk(KERN_INFO "mtd: partition \"%s\" created automatically, ofs=0x%x, len=0x%x\n",
		ROOTFS_SPLIT_NAME, split_offset, split_size);

	__mtd_add_partition(master, ROOTFS_SPLIT_NAME, split_offset,
			    split_size, false);
}

#define UBOOT_MAGIC	0x27051956

static void split_uimage(struct mtd_info *master, struct mtd_part *part)
{
	struct {
		__be32 magic;
		__be32 pad[2];
		__be32 size;
	} hdr;
	size_t len;

	if (mtd_read(master, part->offset, sizeof(hdr), &len, (void *) &hdr))
		return;

	if (len != sizeof(hdr) || hdr.magic != cpu_to_be32(UBOOT_MAGIC))
		return;

	len = be32_to_cpu(hdr.size) + 0x40;
	len = mtd_pad_erasesize(master, part->offset, len);
	if (len + master->erasesize > part->mtd.size)
		return;

	if (config_enabled(CONFIG_MTD_SPLIT_UIMAGE_FW))
		pr_err("Dedicated partitioner didn't split firmware partition, please fill a bug report!\n");
	else
		pr_warn("Support for built-in firmware splitter will be removed, please use CONFIG_MTD_SPLIT_UIMAGE_FW\n");

	__mtd_add_partition(master, "rootfs", part->offset + len,
			    part->mtd.size - len, false);
}

#ifdef CONFIG_MTD_SPLIT_FIRMWARE_NAME
#define SPLIT_FIRMWARE_NAME	CONFIG_MTD_SPLIT_FIRMWARE_NAME
#else
#define SPLIT_FIRMWARE_NAME	"unused"
#endif

static void split_firmware(struct mtd_info *master, struct mtd_part *part)
{
	int ret;

	ret = run_parsers_by_type(part, MTD_PARSER_TYPE_FIRMWARE);
	if (ret > 0)
		return;

	if (config_enabled(CONFIG_MTD_UIMAGE_SPLIT))
		split_uimage(master, part);
}

void __weak arch_split_mtd_part(struct mtd_info *master, const char *name,
                                int offset, int size)
{
}

static void mtd_partition_split(struct mtd_info *master, struct mtd_part *part)
{
	static int rootfs_found = 0;

	if (rootfs_found)
		return;

	if (!strcmp(part->mtd.name, "rootfs")) {
		int num = run_parsers_by_type(part, MTD_PARSER_TYPE_ROOTFS);

		if (num <= 0 && config_enabled(CONFIG_MTD_ROOTFS_SPLIT))
			split_rootfs_data(master, part);

		rootfs_found = 1;
	}

	if (!strcmp(part->mtd.name, SPLIT_FIRMWARE_NAME) &&
	    config_enabled(CONFIG_MTD_SPLIT_FIRMWARE))
		split_firmware(master, part);

	arch_split_mtd_part(master, part->mtd.name, part->offset,
			    part->mtd.size);
}
/*
 * This function, given a master MTD object and a partition table, creates
 * and registers slave MTD objects which are bound to the master according to
 * the partition definitions.
 *
 * We don't register the master, or expect the caller to have done so,
 * for reasons of data integrity.
 */

int add_mtd_partitions(struct mtd_info *master,
		       const struct mtd_partition *parts,
		       int nbparts)
{
	struct mtd_part *slave;
	uint64_t cur_offset = 0;
	int i;

	printk(KERN_NOTICE "Creating %d MTD partitions on \"%s\":\n", nbparts, master->name);

	for (i = 0; i < nbparts; i++) {
		slave = allocate_partition(master, parts + i, i, cur_offset);
		if (IS_ERR(slave))
			return PTR_ERR(slave);

		mutex_lock(&mtd_partitions_mutex);
		list_add(&slave->list, &mtd_partitions);
		mutex_unlock(&mtd_partitions_mutex);

		add_mtd_device(&slave->mtd);
		mtd_partition_split(master, slave);

		cur_offset = slave->offset + slave->mtd.size;
	}

	return 0;
}

static DEFINE_SPINLOCK(part_parser_lock);
static LIST_HEAD(part_parsers);

static struct mtd_part_parser *get_partition_parser(const char *name)
{
	struct mtd_part_parser *p, *ret = NULL;

	spin_lock(&part_parser_lock);

	list_for_each_entry(p, &part_parsers, list)
		if (!strcmp(p->name, name) && try_module_get(p->owner)) {
			ret = p;
			break;
		}

	spin_unlock(&part_parser_lock);

	return ret;
}

#define put_partition_parser(p) do { module_put((p)->owner); } while (0)

static struct mtd_part_parser *
get_partition_parser_by_type(enum mtd_parser_type type,
			     struct mtd_part_parser *start)
{
	struct mtd_part_parser *p, *ret = NULL;

	spin_lock(&part_parser_lock);

	p = list_prepare_entry(start, &part_parsers, list);
	if (start)
		put_partition_parser(start);

	list_for_each_entry_continue(p, &part_parsers, list) {
		if (p->type == type && try_module_get(p->owner)) {
			ret = p;
			break;
		}
	}

	spin_unlock(&part_parser_lock);

	return ret;
}

void register_mtd_parser(struct mtd_part_parser *p)
{
	spin_lock(&part_parser_lock);
	list_add(&p->list, &part_parsers);
	spin_unlock(&part_parser_lock);
}
EXPORT_SYMBOL_GPL(register_mtd_parser);

void deregister_mtd_parser(struct mtd_part_parser *p)
{
	spin_lock(&part_parser_lock);
	list_del(&p->list);
	spin_unlock(&part_parser_lock);
}
EXPORT_SYMBOL_GPL(deregister_mtd_parser);

/*
 * Do not forget to update 'parse_mtd_partitions()' kerneldoc comment if you
 * are changing this array!
 */
static const char * const default_mtd_part_types[] = {
	"cmdlinepart",
	"ofpart",
	NULL
};

/**
 * parse_mtd_partitions - parse MTD partitions
 * @master: the master partition (describes whole MTD device)
 * @types: names of partition parsers to try or %NULL
 * @pparts: array of partitions found is returned here
 * @data: MTD partition parser-specific data
 *
 * This function tries to find partition on MTD device @master. It uses MTD
 * partition parsers, specified in @types. However, if @types is %NULL, then
 * the default list of parsers is used. The default list contains only the
 * "cmdlinepart" and "ofpart" parsers ATM.
 * Note: If there are more then one parser in @types, the kernel only takes the
 * partitions parsed out by the first parser.
 *
 * This function may return:
 * o a negative error code in case of failure
 * o zero if no partitions were found
 * o a positive number of found partitions, in which case on exit @pparts will
 *   point to an array containing this number of &struct mtd_info objects.
 */
int parse_mtd_partitions(struct mtd_info *master, const char *const *types,
			 struct mtd_partition **pparts,
			 struct mtd_part_parser_data *data)
{
	struct mtd_part_parser *parser;
	int ret = 0;

	if (!types)
		types = default_mtd_part_types;

	for ( ; ret <= 0 && *types; types++) {
		parser = get_partition_parser(*types);
		if (!parser && !request_module("%s", *types))
			parser = get_partition_parser(*types);
		if (!parser)
			continue;
		ret = (*parser->parse_fn)(master, pparts, data);
		put_partition_parser(parser);
		if (ret > 0) {
			printk(KERN_NOTICE "%d %s partitions found on MTD device %s\n",
			       ret, parser->name, master->name);
			break;
		}
	}
	return ret;
}

int parse_mtd_partitions_by_type(struct mtd_info *master,
				 enum mtd_parser_type type,
				 struct mtd_partition **pparts,
				 struct mtd_part_parser_data *data)
{
	struct mtd_part_parser *prev = NULL;
	int ret = 0;

	while (1) {
		struct mtd_part_parser *parser;

		parser = get_partition_parser_by_type(type, prev);
		if (!parser)
			break;

		ret = (*parser->parse_fn)(master, pparts, data);

		if (ret > 0) {
			put_partition_parser(parser);
			printk(KERN_NOTICE
			       "%d %s partitions found on MTD device %s\n",
			       ret, parser->name, master->name);
			break;
		}

		prev = parser;
	}

	return ret;
}
EXPORT_SYMBOL_GPL(parse_mtd_partitions_by_type);

int mtd_is_partition(const struct mtd_info *mtd)
{
	struct mtd_part *part;
	int ispart = 0;

	mutex_lock(&mtd_partitions_mutex);
	list_for_each_entry(part, &mtd_partitions, list)
		if (&part->mtd == mtd) {
			ispart = 1;
			break;
		}
	mutex_unlock(&mtd_partitions_mutex);

	return ispart;
}
EXPORT_SYMBOL_GPL(mtd_is_partition);

struct mtd_info *mtdpart_get_master(const struct mtd_info *mtd)
{
	if (!mtd_is_partition(mtd))
		return (struct mtd_info *)mtd;

	return PART(mtd)->master;
}
EXPORT_SYMBOL_GPL(mtdpart_get_master);

uint64_t mtdpart_get_offset(const struct mtd_info *mtd)
{
	if (!mtd_is_partition(mtd))
		return 0;

	return PART(mtd)->offset;
}
EXPORT_SYMBOL_GPL(mtdpart_get_offset);

/* Returns the size of the entire flash chip */
uint64_t mtd_get_device_size(const struct mtd_info *mtd)
{
	if (!mtd_is_partition(mtd))
		return mtd->size;

	return PART(mtd)->master->size;
}
EXPORT_SYMBOL_GPL(mtd_get_device_size);

mtd_device_parse_register()->parse_mtd_partitions() -> tplink_parse_partitions()

从代码()中可以看到，这里从Flash中得到了5个分区：u-boot, kernel, rootfs, art和firmware分区，其中firmware分区中又包含了kernel和rootfs分区，官方image也就在这里面。下面是将rootfs分区分解出rootfs_data分区：

-> add_mtd_partitions()

-> mtd_partition_split(“rootfs”)

-> split_rootfs_data(“rootfs”)

-> __mtd_add_partition(“rootfs_data”)

NOTE:

rootfs分区使用的文件系统为SquashFS, 是ro (readonly)的文件系统。

rootfs_data分区使用的文件系统为JFFS2(全称为Journalling Flash File System v2 ), 是带日志的，不怕意外断电，所以请放心使用。

相关文档请看这里：

1. https://wiki.openwrt.org/doc/techref/flash.layout
2. https://dev.openwrt.org/browser/trunk/target/linux/ar71xx/files/drivers/mtd/tplinkpart.c?rev=46662
3. https://wiki.openwrt.org/doc/techref/filesystems#squashfs
4. https://wiki.openwrt.org/doc/techref/filesystems#overlayfs