MTD(memory technology device):内存技术设备,是linux用于描述ROM,NAND,NOR等设备的子系统的抽象,MTD设备可以按块读写也可以按字节读写,也就是说MTD设备既可以是块设备也可以是字符设备,块设备(mtdblackx)操作针对文件系统,字符设备(mtdx)操作主要针对格式化等操作的测试用。

一个MTD设备的描述为mtd_info这个结构体,填充好这个结构体,然后调用add_mtd_device添加mtd设备函数就可以注册MTD设备了。在内核的源代码中,mtdram.c是一个很简单的例子,他把一块内存空间模拟了一个MTD device,研究MTD的框架,从这个mtdram.c开始:

  1. /*
  2. * mtdram - a test mtd device
  3. * Author: Alexander Larsson <alex@cendio.se>
  4. *
  5. * Copyright (c) 1999 Alexander Larsson <alex@cendio.se>
  6. * Copyright (c) 2005 Joern Engel <joern@wh.fh-wedel.de>
  7. *
  8. * This code is GPL
  9. *
  10. */
  11. #include <linux/module.h>
  12. #include <linux/slab.h>
  13. #include <linux/ioport.h>
  14. #include <linux/vmalloc.h>
  15. #include <linux/init.h>
  16. #include <linux/mtd/compatmac.h>
  17. #include <linux/mtd/mtd.h>
  18. #include <linux/mtd/mtdram.h>
  19. static unsigned long total_size = CONFIG_MTDRAM_TOTAL_SIZE;
  20. static unsigned long erase_size = CONFIG_MTDRAM_ERASE_SIZE;
  21. #define MTDRAM_TOTAL_SIZE (total_size * 1024)
  22. #define MTDRAM_ERASE_SIZE (erase_size * 1024)
  23. #ifdef MODULE
  24. module_param(total_size, ulong, 0);
  25. MODULE_PARM_DESC(total_size, "Total device size in KiB");
  26. module_param(erase_size, ulong, 0);
  27. MODULE_PARM_DESC(erase_size, "Device erase block size in KiB");
  28. #endif
  29. // We could store these in the mtd structure, but we only support 1 device..
  30. static struct mtd_info *mtd_info;
  31. static int ram_erase(struct mtd_info *mtd, struct erase_info *instr)
  32. {
  33. if (instr->addr + instr->len > mtd->size)
  34. return -EINVAL;
  35. memset((char *)mtd->priv + instr->addr, 0xff, instr->len);
  36. instr->state = MTD_ERASE_DONE;
  37. mtd_erase_callback(instr);
  38. return 0;
  39. }
  40. static int ram_point(struct mtd_info *mtd, loff_t from, size_t len,
  41. size_t *retlen, void **virt, resource_size_t *phys)
  42. {
  43. if (from + len > mtd->size)
  44. return -EINVAL;
  45. /* can we return a physical address with this driver? */
  46. if (phys)
  47. return -EINVAL;
  48. *virt = mtd->priv + from;
  49. *retlen = len;
  50. return 0;
  51. }
  52. static void ram_unpoint(struct mtd_info *mtd, loff_t from, size_t len)
  53. {
  54. }
  55. /*
  56. * Allow NOMMU mmap() to directly map the device (if not NULL)
  57. * - return the address to which the offset maps
  58. * - return -ENOSYS to indicate refusal to do the mapping
  59. */
  60. static unsigned long ram_get_unmapped_area(struct mtd_info *mtd,
  61. unsigned long len,
  62. unsigned long offset,
  63. unsigned long flags)
  64. {
  65. return (unsigned long) mtd->priv + offset;
  66. }
  67. static int ram_read(struct mtd_info *mtd, loff_t from, size_t len,
  68. size_t *retlen, u_char *buf)
  69. {
  70. if (from + len > mtd->size)
  71. return -EINVAL;
  72. memcpy(buf, mtd->priv + from, len);
  73. *retlen = len;
  74. return 0;
  75. }
  76. static int ram_write(struct mtd_info *mtd, loff_t to, size_t len,
  77. size_t *retlen, const u_char *buf)
  78. {
  79. if (to + len > mtd->size)
  80. return -EINVAL;
  81. memcpy((char *)mtd->priv + to, buf, len);
  82. *retlen = len;
  83. return 0;
  84. }
  85. static void __exit cleanup_mtdram(void)
  86. {
  87. if (mtd_info) {
  88. del_mtd_device(mtd_info);
  89. vfree(mtd_info->priv);
  90. kfree(mtd_info);
  91. }
  92. }
  93. int mtdram_init_device(struct mtd_info *mtd, void *mapped_address,
  94. unsigned long size, char *name)
  95. {
  96. memset(mtd, 0, sizeof(*mtd));
  97. /* Setup the MTD structure */
  98. mtd->name = name;
  99. mtd->type = MTD_RAM;
  100. mtd->flags = MTD_CAP_RAM;
  101. mtd->size = size;
  102. mtd->writesize = 1;
  103. mtd->erasesize = MTDRAM_ERASE_SIZE;
  104. mtd->priv = mapped_address;
  105. mtd->owner = THIS_MODULE;
  106. mtd->erase = ram_erase;
  107. mtd->point = ram_point;
  108. mtd->unpoint = ram_unpoint;
  109. mtd->get_unmapped_area = ram_get_unmapped_area;
  110. mtd->read = ram_read;
  111. mtd->write = ram_write;
  112. if (add_mtd_device(mtd)) { //填充好mtd_info之后注册这个mtd设备
  113. return -EIO;
  114. }
  115. return 0;
  116. }
  117. static int __init init_mtdram(void)
  118. {
  119. void *addr;
  120. int err;
  121. if (!total_size)
  122. return -EINVAL;
  123. /* Allocate some memory */
  124. mtd_info = kmalloc(sizeof(struct mtd_info), GFP_KERNEL); //分配mtd_info
  125. if (!mtd_info)
  126. return -ENOMEM;
  127. addr = vmalloc(MTDRAM_TOTAL_SIZE); //开辟一段内存用来模拟MTD设备
  128. if (!addr) {
  129. kfree(mtd_info);
  130. mtd_info = NULL;
  131. return -ENOMEM;
  132. }
  133. err = mtdram_init_device(mtd_info, addr, MTDRAM_TOTAL_SIZE, "mtdram test device");
  134. if (err) {
  135. vfree(addr);
  136. kfree(mtd_info);
  137. mtd_info = NULL;
  138. return err;
  139. }
  140. memset(mtd_info->priv, 0xff, MTDRAM_TOTAL_SIZE);
  141. return err;
  142. }
  143. module_init(init_mtdram);
  144. module_exit(cleanup_mtdram);
  145. MODULE_LICENSE("GPL");
  146. MODULE_AUTHOR("Alexander Larsson <alexl@redhat.com>");
  147. MODULE_DESCRIPTION("Simulated MTD driver for testing");

这是一个很简单的mtd设备驱动,以一块ram来模拟一个mtd设备,从上面代码可以看到,一个mtd设备的注册就是先填充好一个mtd_info,这个结构体提供设备的硬件信息以及读写擦除等操作方法。注册这个结构体就完成了一个mtd设备的添加。这里对应的是ram设备,读写是直接操作内存的,如果是nandflash和norflash设备,对读写擦除等操作函数比较复杂,但是最终mtd的设备都要调用add_mtd_device这个函数来注册,下面来分析到底这个函数做了什么来注册一个mtd设备的:

  1. int add_mtd_device(struct mtd_info *mtd)
  2. {
  3. int i;
  4. if (!mtd->backing_dev_info) {
  5. switch (mtd->type) {
  6. case MTD_RAM:
  7. mtd->backing_dev_info = &mtd_bdi_rw_mappable;
  8. break;
  9. case MTD_ROM:
  10. mtd->backing_dev_info = &mtd_bdi_ro_mappable;
  11. break;
  12. default:
  13. mtd->backing_dev_info = &mtd_bdi_unmappable;
  14. break;
  15. }
  16. }
  17. BUG_ON(mtd->writesize == 0);
  18. mutex_lock(&mtd_table_mutex);
  19. for (i=0; i < MAX_MTD_DEVICES; i++)
  20. if (!mtd_table[i]) {
  21. struct mtd_notifier *not;
  22. mtd_table[i] = mtd;
  23. mtd->index = i;
  24. mtd->usecount = 0;
  25. if (is_power_of_2(mtd->erasesize))
  26. mtd->erasesize_shift = ffs(mtd->erasesize) - 1;
  27. else
  28. mtd->erasesize_shift = 0;
  29. if (is_power_of_2(mtd->writesize))
  30. mtd->writesize_shift = ffs(mtd->writesize) - 1;
  31. else
  32. mtd->writesize_shift = 0;
  33. mtd->erasesize_mask = (1 << mtd->erasesize_shift) - 1;
  34. mtd->writesize_mask = (1 << mtd->writesize_shift) - 1;
  35. /* Some chips always power up locked. Unlock them now */
  36. if ((mtd->flags & MTD_WRITEABLE)
  37. && (mtd->flags & MTD_POWERUP_LOCK) && mtd->unlock) {
  38. if (mtd->unlock(mtd, 0, mtd->size))
  39. printk(KERN_WARNING
  40. "%s: unlock failed, "
  41. "writes may not work\n",
  42. mtd->name);
  43. }
  44. /* Caller should have set dev.parent to match the
  45. * physical device.
  46. */
  47. mtd->dev.type = &mtd_devtype;
  48. mtd->dev.class = &mtd_class;
  49. mtd->dev.devt = MTD_DEVT(i);
  50. dev_set_name(&mtd->dev, "mtd%d", i); //设置mtd设备名称
  51. dev_set_drvdata(&mtd->dev, mtd);
  52. if (device_register(&mtd->dev) != 0) { //注册mtd设备(会自动创建mtd设备可读写的节点)
  53. mtd_table[i] = NULL;
  54. break;
  55. }
  56. if (MTD_DEVT(i))
  57. device_create(&mtd_class, mtd->dev.parent, //创建mtd设备只读的节点
  58. MTD_DEVT(i) + 1,
  59. NULL, "mtd%dro", i);
  60. DEBUG(0, "mtd: Giving out device %d to %s\n",i, mtd->name);
  61. /* No need to get a refcount on the module containing
  62. the notifier, since we hold the mtd_table_mutex */
  63. list_for_each_entry(not, &mtd_notifiers, list)
  64. not->add(mtd); //把这个mtd device注册到mtd
  65. mutex_unlock(&mtd_table_mutex);
  66. /* We _know_ we aren't being removed, because
  67. our caller is still holding us here. So none
  68. of this try_ nonsense, and no bitching about it
  69. either. :) */
  70. __module_get(THIS_MODULE);
  71. return 0;
  72. }
  73. mutex_unlock(&mtd_table_mutex);
  74. return 1;
  75. }

可以看出注册device的时候,需要调用mtd_notifiers链表里面的add函数,这个函数指针在哪里被添加进去的?

  1. void register_mtd_user (struct mtd_notifier *new)
  2. {
  3. int i;
  4. mutex_lock(&mtd_table_mutex);
  5. list_add(&new->list, &mtd_notifiers); //new添加到mtd_notifiers链表
  6. __module_get(THIS_MODULE);
  7. for (i=0; i< MAX_MTD_DEVICES; i++)
  8. if (mtd_table[i])
  9. new->add(mtd_table[i]);
  10. mutex_unlock(&mtd_table_mutex);
  11. }

那么register_mtd_user是谁调用的?查看代码可以知道在mtdchar.c与mtdblock.c以及mtdblock_ro.c里面注册MTD字符设备与MTD块设备的时候调用的,所以可以知道这个链表放的就是支持mtd设备的所有驱动,都放在这个链表里面,在执行add_mtd_device里面的

list_for_each_entry(not, &mtd_notifiers, list)
not->add(mtd);

的时候,一个for循环调用不同驱动(字符,块,只读块驱动)的add函数来添加这个device到不同的驱动。这里以块设备驱动为例,如果添加到块驱动,那么:

  1. static struct mtd_notifier blktrans_notifier = {
  2. .add = blktrans_notify_add,
  3. .remove = blktrans_notify_remove,
  4. };

调用add就是调用:

  1. static void blktrans_notify_add(struct mtd_info *mtd)
  2. {
  3. struct mtd_blktrans_ops *tr;
  4. if (mtd->type == MTD_ABSENT)
  5. return;
  6. list_for_each_entry(tr, &blktrans_majors, list)
  7. tr->add_mtd(tr, mtd);
  8. }

可以知道执行blktrans_majors链表里面的add_mtd,这个链表的元素通过下面函数添加进去:

  1. int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
  2. {
  3. int ret, i;
  4. /* Register the notifier if/when the first device type is
  5. registered, to prevent the link/init ordering from fucking
  6. us over. */
  7. if (!blktrans_notifier.list.next)
  8. register_mtd_user(&blktrans_notifier);
  9. tr->blkcore_priv = kzalloc(sizeof(*tr->blkcore_priv), GFP_KERNEL);
  10. if (!tr->blkcore_priv)
  11. return -ENOMEM;
  12. mutex_lock(&mtd_table_mutex);
  13. ret = register_blkdev(tr->major, tr->name);
  14. if (ret) {
  15. printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
  16. tr->name, tr->major, ret);
  17. kfree(tr->blkcore_priv);
  18. mutex_unlock(&mtd_table_mutex);
  19. return ret;
  20. }
  21. spin_lock_init(&tr->blkcore_priv->queue_lock);
  22. tr->blkcore_priv->rq = blk_init_queue(mtd_blktrans_request, &tr->blkcore_priv->queue_lock);
  23. if (!tr->blkcore_priv->rq) {
  24. unregister_blkdev(tr->major, tr->name);
  25. kfree(tr->blkcore_priv);
  26. mutex_unlock(&mtd_table_mutex);
  27. return -ENOMEM;
  28. }
  29. tr->blkcore_priv->rq->queuedata = tr;
  30. blk_queue_logical_block_size(tr->blkcore_priv->rq, tr->blksize);
  31. if (tr->discard)
  32. queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
  33. tr->blkcore_priv->rq);
  34. tr->blkshift = ffs(tr->blksize) - 1;
  35. tr->blkcore_priv->thread = kthread_run(mtd_blktrans_thread, tr,
  36. "%sd", tr->name);
  37. if (IS_ERR(tr->blkcore_priv->thread)) {
  38. int ret = PTR_ERR(tr->blkcore_priv->thread);
  39. blk_cleanup_queue(tr->blkcore_priv->rq);
  40. unregister_blkdev(tr->major, tr->name);
  41. kfree(tr->blkcore_priv);
  42. mutex_unlock(&mtd_table_mutex);
  43. return ret;
  44. }
  45. INIT_LIST_HEAD(&tr->devs);
  46. list_add(&tr->list, &blktrans_majors); //添加这个块驱动到链表
  47. for (i=0; i<MAX_MTD_DEVICES; i++) { //注册块驱动的时候添加所有mtd的块设备
  48. if (mtd_table[i] && mtd_table[i]->type != MTD_ABSENT)
  49. tr->add_mtd(tr, mtd_table[i]);
  50. }
  51. mutex_unlock(&mtd_table_mutex);
  52. return 0;
  53. }

这个函数就是注册一个块驱动,然后添加所有mtd的块设备。所以最终的核心就是add_mtd这个,他在mtd块设备里面是mtdblock_add_mtd函数,这个函数最终会调用下面函数来添加一个MTD块设备:

  1. int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
  2. {
  3. struct mtd_blktrans_ops *tr = new->tr;
  4. struct mtd_blktrans_dev *d;
  5. int last_devnum = -1;
  6. struct gendisk *gd;
  7. if (mutex_trylock(&mtd_table_mutex)) {
  8. mutex_unlock(&mtd_table_mutex);
  9. BUG();
  10. }
  11. list_for_each_entry(d, &tr->devs, list) {
  12. if (new->devnum == -1) {
  13. /* Use first free number */
  14. if (d->devnum != last_devnum+1) {
  15. /* Found a free devnum. Plug it in here */
  16. new->devnum = last_devnum+1;
  17. list_add_tail(&new->list, &d->list);
  18. goto added;
  19. }
  20. } else if (d->devnum == new->devnum) {
  21. /* Required number taken */
  22. return -EBUSY;
  23. } else if (d->devnum > new->devnum) {
  24. /* Required number was free */
  25. list_add_tail(&new->list, &d->list);
  26. goto added;
  27. }
  28. last_devnum = d->devnum;
  29. }
  30. if (new->devnum == -1)
  31. new->devnum = last_devnum+1;
  32. if ((new->devnum << tr->part_bits) > 256) {
  33. return -EBUSY;
  34. }
  35. list_add_tail(&new->list, &tr->devs);
  36. added:
  37. mutex_init(&new->lock);
  38. if (!tr->writesect)
  39. new->readonly = 1;
  40. gd = alloc_disk(1 << tr->part_bits); //分配disk
  41. if (!gd) {
  42. list_del(&new->list);
  43. return -ENOMEM;
  44. }
  45. gd->major = tr->major;
  46. gd->first_minor = (new->devnum) << tr->part_bits;
  47. gd->fops = &mtd_blktrans_ops;
  48. if (tr->part_bits)
  49. if (new->devnum < 26)
  50. snprintf(gd->disk_name, sizeof(gd->disk_name),
  51. "%s%c", tr->name, 'a' + new->devnum);
  52. else
  53. snprintf(gd->disk_name, sizeof(gd->disk_name),
  54. "%s%c%c", tr->name,
  55. 'a' - 1 + new->devnum / 26,
  56. 'a' + new->devnum % 26);
  57. else
  58. snprintf(gd->disk_name, sizeof(gd->disk_name),
  59. "%s%d", tr->name, new->devnum);
  60. /* 2.5 has capacity in units of 512 bytes while still
  61. having BLOCK_SIZE_BITS set to 10. Just to keep us amused. */
  62. set_capacity(gd, (new->size * tr->blksize) >> 9);
  63. gd->private_data = new;
  64. new->blkcore_priv = gd;
  65. gd->queue = tr->blkcore_priv->rq;
  66. gd->driverfs_dev = &new->mtd->dev;
  67. if (new->readonly)
  68. set_disk_ro(gd, 1);
  69. add_disk(gd); //添加disk
  70. return 0;
  71. }

alloc_disk与add_disk这在之前分析块设备驱动框架的时候已经分析了,这两个就是注册块设备的基本函数。而如果是mtd字符设备,就会调用字符设备的添加函数,所以add_mtd_device这个函数就是这样来添加mtd设备的。
mtd设备驱动由块设备,字符设备,只读块设备等类型:

MTD块driver(针对文件系统):

  1. static struct mtd_blktrans_ops mtdblock_tr = {
  2. .name = "mtdblock",
  3. .major = 31,
  4. .part_bits = 0,
  5. .blksize = 512,
  6. .open = mtdblock_open,
  7. .flush = mtdblock_flush,
  8. .release = mtdblock_release,
  9. .readsect = mtdblock_readsect,
  10. .writesect = mtdblock_writesect,
  11. .add_mtd = mtdblock_add_mtd,
  12. .remove_dev = mtdblock_remove_dev,
  13. .owner = THIS_MODULE,
  14. };
  15. static int __init init_mtdblock(void)
  16. {
  17. mutex_init(&mtdblks_lock);
  18. return register_mtd_blktrans(&mtdblock_tr);
  19. }
  20. static void __exit cleanup_mtdblock(void)
  21. {
  22. deregister_mtd_blktrans(&mtdblock_tr);
  23. }
  24. module_init(init_mtdblock);
  25. module_exit(cleanup_mtdblock);

MTD字符driver(支持块设备像字符设备那样去操作,一般用作测试)

  1. static int __init init_mtdchar(void)
  2. {
  3. int ret;
  4. ret = __register_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS,"mtd", &mtd_fops); //注册字符设备,捆绑mtd_fops
  5. if (ret < 0) {
  6. pr_notice("Can't allocate major number %d for Memory Technology Devices.\n", MTD_CHAR_MAJOR);
  7. return ret;
  8. }
  9. ret = register_filesystem(&mtd_inodefs_type); //注册mtd_inodefs_type文件系统
  10. if (ret) {
  11. pr_notice("Can't register mtd_inodefs filesystem: %d\n", ret);
  12. goto err_unregister_chdev;
  13. }
  14. mtd_inode_mnt = kern_mount(&mtd_inodefs_type); //挂载mtd_inodefs_type文件系统
  15. if (IS_ERR(mtd_inode_mnt)) {
  16. ret = PTR_ERR(mtd_inode_mnt);
  17. pr_notice("Error mounting mtd_inodefs filesystem: %d\n", ret);
  18. goto err_unregister_filesystem;
  19. }
  20. register_mtd_user(&mtdchar_notifier); //注册到链表
  21. return ret;
  22. err_unregister_filesystem:
  23. unregister_filesystem(&mtd_inodefs_type);
  24. err_unregister_chdev:
  25. __unregister_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS, "mtd");
  26. return ret;
  27. }

MTD的框架跟输入子系统一样类似的分离框架,一边注册驱动(driver),一边注册设备(device),驱动有字符,块,只读块,系统开机会注册mtd设备的驱动同时添加已注册的设备。

MTD驱动端:这里可以注册mtd的字符与块设备,只读块驱动,分别对应内核代码的mtdblock.c与mtdchar.c还有只读的mtdblock_ro.c

MTD设备端:调用add_mtd_device注册设备

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