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* block2mtd.c - create an mtd from a block device
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* Copyright (C) 2001,2002 Simon Evans <spse@secret.org.uk>
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* Copyright (C) 2004-2006 Joern Engel <joern@wh.fh-wedel.de>
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#include <linux/module.h>
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#include <linux/blkdev.h>
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#include <linux/bio.h>
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#include <linux/pagemap.h>
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#include <linux/list.h>
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#include <linux/init.h>
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#include <linux/mtd/mtd.h>
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#include <linux/buffer_head.h>
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#include <linux/mutex.h>
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#include <linux/mount.h>
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#include <linux/slab.h>
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#define ERROR(fmt, args...) printk(KERN_ERR "block2mtd: " fmt "\n" , ## args)
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#define INFO(fmt, args...) printk(KERN_INFO "block2mtd: " fmt "\n" , ## args)
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/* Info for the block device */
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struct block2mtd_dev {
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struct list_head list;
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struct block_device *blkdev;
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struct mutex write_mutex;
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/* Static info about the MTD, used in cleanup_module */
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static LIST_HEAD(blkmtd_device_list);
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static struct page *page_read(struct address_space *mapping, int index)
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return read_mapping_page(mapping, index, NULL);
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/* erase a specified part of the device */
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static int _block2mtd_erase(struct block2mtd_dev *dev, loff_t to, size_t len)
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struct address_space *mapping = dev->blkdev->bd_inode->i_mapping;
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int index = to >> PAGE_SHIFT; // page index
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int pages = len >> PAGE_SHIFT;
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page = page_read(mapping, index);
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max = page_address(page) + PAGE_SIZE;
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for (p=page_address(page); p<max; p++)
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memset(page_address(page), 0xff, PAGE_SIZE);
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page_cache_release(page);
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static int block2mtd_erase(struct mtd_info *mtd, struct erase_info *instr)
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struct block2mtd_dev *dev = mtd->priv;
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size_t from = instr->addr;
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size_t len = instr->len;
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instr->state = MTD_ERASING;
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mutex_lock(&dev->write_mutex);
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err = _block2mtd_erase(dev, from, len);
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mutex_unlock(&dev->write_mutex);
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ERROR("erase failed err = %d", err);
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instr->state = MTD_ERASE_FAILED;
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instr->state = MTD_ERASE_DONE;
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mtd_erase_callback(instr);
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static int block2mtd_read(struct mtd_info *mtd, loff_t from, size_t len,
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size_t *retlen, u_char *buf)
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struct block2mtd_dev *dev = mtd->priv;
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int index = from >> PAGE_SHIFT;
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int offset = from & (PAGE_SIZE-1);
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if (from > mtd->size)
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if (from + len > mtd->size)
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len = mtd->size - from;
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if ((offset + len) > PAGE_SIZE)
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cpylen = PAGE_SIZE - offset; // multiple pages
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cpylen = len; // this page
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page = page_read(dev->blkdev->bd_inode->i_mapping, index);
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return PTR_ERR(page);
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memcpy(buf, page_address(page) + offset, cpylen);
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page_cache_release(page);
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/* write data to the underlying device */
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static int _block2mtd_write(struct block2mtd_dev *dev, const u_char *buf,
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loff_t to, size_t len, size_t *retlen)
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struct address_space *mapping = dev->blkdev->bd_inode->i_mapping;
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int index = to >> PAGE_SHIFT; // page index
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int offset = to & ~PAGE_MASK; // page offset
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if ((offset+len) > PAGE_SIZE)
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cpylen = PAGE_SIZE - offset; // multiple pages
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cpylen = len; // this page
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page = page_read(mapping, index);
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return PTR_ERR(page);
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if (memcmp(page_address(page)+offset, buf, cpylen)) {
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memcpy(page_address(page) + offset, buf, cpylen);
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set_page_dirty(page);
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page_cache_release(page);
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static int block2mtd_write(struct mtd_info *mtd, loff_t to, size_t len,
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size_t *retlen, const u_char *buf)
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struct block2mtd_dev *dev = mtd->priv;
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if (to + len > mtd->size)
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len = mtd->size - to;
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mutex_lock(&dev->write_mutex);
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err = _block2mtd_write(dev, buf, to, len, retlen);
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mutex_unlock(&dev->write_mutex);
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/* sync the device - wait until the write queue is empty */
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static void block2mtd_sync(struct mtd_info *mtd)
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struct block2mtd_dev *dev = mtd->priv;
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sync_blockdev(dev->blkdev);
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static void block2mtd_free_device(struct block2mtd_dev *dev)
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kfree(dev->mtd.name);
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invalidate_mapping_pages(dev->blkdev->bd_inode->i_mapping,
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blkdev_put(dev->blkdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
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/* FIXME: ensure that mtd->size % erase_size == 0 */
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static struct block2mtd_dev *add_device(char *devname, int erase_size)
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const fmode_t mode = FMODE_READ | FMODE_WRITE | FMODE_EXCL;
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struct block_device *bdev;
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struct block2mtd_dev *dev;
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dev = kzalloc(sizeof(struct block2mtd_dev), GFP_KERNEL);
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/* Get a handle on the device */
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bdev = blkdev_get_by_path(devname, mode, dev);
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/* We might not have rootfs mounted at this point. Try
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to resolve the device name by other means. */
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dev_t devt = name_to_dev_t(devname);
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bdev = blkdev_get_by_dev(devt, mode, dev);
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ERROR("error: cannot open device %s", devname);
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if (MAJOR(bdev->bd_dev) == MTD_BLOCK_MAJOR) {
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ERROR("attempting to use an MTD device as a block device");
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mutex_init(&dev->write_mutex);
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/* Setup the MTD structure */
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/* make the name contain the block device in */
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name = kasprintf(GFP_KERNEL, "block2mtd: %s", devname);
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dev->mtd.name = name;
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dev->mtd.size = dev->blkdev->bd_inode->i_size & PAGE_MASK;
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dev->mtd.erasesize = erase_size;
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dev->mtd.writesize = 1;
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dev->mtd.type = MTD_RAM;
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dev->mtd.flags = MTD_CAP_RAM;
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dev->mtd.erase = block2mtd_erase;
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dev->mtd.write = block2mtd_write;
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dev->mtd.writev = default_mtd_writev;
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dev->mtd.sync = block2mtd_sync;
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dev->mtd.read = block2mtd_read;
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dev->mtd.owner = THIS_MODULE;
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if (mtd_device_register(&dev->mtd, NULL, 0)) {
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/* Device didn't get added, so free the entry */
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list_add(&dev->list, &blkmtd_device_list);
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INFO("mtd%d: [%s] erase_size = %dKiB [%d]", dev->mtd.index,
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dev->mtd.name + strlen("block2mtd: "),
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dev->mtd.erasesize >> 10, dev->mtd.erasesize);
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block2mtd_free_device(dev);
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/* This function works similar to reguler strtoul. In addition, it
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* allows some suffixes for a more human-readable number format:
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* ki, Ki, kiB, KiB - multiply result with 1024
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* Mi, MiB - multiply result with 1024^2
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* Gi, GiB - multiply result with 1024^3
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static int ustrtoul(const char *cp, char **endp, unsigned int base)
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unsigned long result = simple_strtoul(cp, endp, base);
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/* By dwmw2 editorial decree, "ki", "Mi" or "Gi" are to be used. */
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if ((*endp)[1] == 'i') {
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if ((*endp)[2] == 'B')
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static int parse_num(size_t *num, const char *token)
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n = (size_t) ustrtoul(token, &endp, 0);
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static inline void kill_final_newline(char *str)
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char *newline = strrchr(str, '\n');
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if (newline && !newline[1])
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#define parse_err(fmt, args...) do { \
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ERROR(fmt, ## args); \
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static int block2mtd_init_called = 0;
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static char block2mtd_paramline[80 + 12]; /* 80 for device, 12 for erase size */
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static int block2mtd_setup2(const char *val)
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char buf[80 + 12]; /* 80 for device, 12 for erase size */
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size_t erase_size = PAGE_SIZE;
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if (strnlen(val, sizeof(buf)) >= sizeof(buf))
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parse_err("parameter too long");
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kill_final_newline(str);
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for (i = 0; i < 2; i++)
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token[i] = strsep(&str, ",");
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parse_err("too many arguments");
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parse_err("no argument");
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if (strlen(name) + 1 > 80)
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parse_err("device name too long");
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ret = parse_num(&erase_size, token[1]);
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parse_err("illegal erase size");
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add_device(name, erase_size);
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static int block2mtd_setup(const char *val, struct kernel_param *kp)
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return block2mtd_setup2(val);
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/* If more parameters are later passed in via
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/sys/module/block2mtd/parameters/block2mtd
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and block2mtd_init() has already been called,
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we can parse the argument now. */
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if (block2mtd_init_called)
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return block2mtd_setup2(val);
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/* During early boot stage, we only save the parameters
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here. We must parse them later: if the param passed
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from kernel boot command line, block2mtd_setup() is
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called so early that it is not possible to resolve
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the device (even kmalloc() fails). Deter that work to
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block2mtd_setup2(). */
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strlcpy(block2mtd_paramline, val, sizeof(block2mtd_paramline));
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module_param_call(block2mtd, block2mtd_setup, NULL, NULL, 0200);
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MODULE_PARM_DESC(block2mtd, "Device to use. \"block2mtd=<dev>[,<erasesize>]\"");
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static int __init block2mtd_init(void)
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if (strlen(block2mtd_paramline))
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ret = block2mtd_setup2(block2mtd_paramline);
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block2mtd_init_called = 1;
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static void __devexit block2mtd_exit(void)
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struct list_head *pos, *next;
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/* Remove the MTD devices */
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list_for_each_safe(pos, next, &blkmtd_device_list) {
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struct block2mtd_dev *dev = list_entry(pos, typeof(*dev), list);
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block2mtd_sync(&dev->mtd);
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mtd_device_unregister(&dev->mtd);
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INFO("mtd%d: [%s] removed", dev->mtd.index,
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dev->mtd.name + strlen("block2mtd: "));
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list_del(&dev->list);
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block2mtd_free_device(dev);
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module_init(block2mtd_init);
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module_exit(block2mtd_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Joern Engel <joern@lazybastard.org>");
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MODULE_DESCRIPTION("Emulate an MTD using a block device");