转：http://www.crifan.com/linux_system_in__dev__mtd_and__dev__mtdblock_distinction_character_devices_and_block_devices_mtd_difference/
1. /dev/mtdN 是Linux 中的MTD架构中，系统自己实现的mtd分区所对应的字符设备，其里面添加了一些ioctl，支持很多命令，如MEMGETINFO，MEMERASE等。
而mtd-util中的flash_eraseall等工具，就是以这些ioctl为基础而实现的工具，实现一些关于Flash的操作。比如，mtd 工具中的 flash_eraseall中的：
if (ioctl(fd, MEMGETINFO, &meminfo) != 0) {
fprintf(stderr, "%s: %s: unable to get MTD device infon", exe_name, mtd_device);
return 1;
}
其中，MEMGETINFO，就是Linux MTD中的drivers/mtd/nand/mtdchar.c中的：
static int mtd_ioctl(struct inode *inode, struct file *file,
u_int cmd, u_long arg)
{
。。。。。
case MEMGETINFO:
info.type = mtd->type;
info.flags = mtd->flags;
info.size = mtd->size;
info.erasesize = mtd->erasesize;
info.writesize = mtd->writesize;
info.oobsize = mtd->oobsize;
/* The below fields are obsolete */
info.ecctype = -1;
info.eccsize = 0;
if (copy_to_user(argp, &info, sizeof(struct mtd_info_user)))
return -EFAULT;
break;
。。。
}
而/dev/mtdblockN，是Nand Flash驱动中，驱动在用add_mtd_partitions()添加MTD设备分区，而生成的对应的块设备。
根据以上内容，也就更加明白，为什么不能用nandwrite,flash_eraseall,flash_erase等工具去对/dev/mtdblockN去操作了。因为/dev/mtdblock中不包含对应的ioctl，不支持你这么操作。
2. mtd char 设备的主设备号是90，而mtd block设备的主设备号是31：
# ls /dev/mtd? -l
crw-r—– 1 root root 90, 0 May 30 2007 /dev/mtd0
crw-r—– 1 root root 90, 2 May 30 2007 /dev/mtd1
crw-r—– 1 root root 90, 4 Jul 17 2009 /dev/mtd2
crw-r—– 1 root root 90, 6 May 30 2007 /dev/mtd3
crwxrwxrwx 1 root root 90, 8 May 30 2007 /dev/mtd4
crwxrwxrwx 1 root root 90, 10 May 30 2007 /dev/mtd5
crwxrwxrwx 1 root root 90, 12 May 30 2007 /dev/mtd6
crwxrwxrwx 1 root root 90, 14 May 30 2007 /dev/mtd7
crwxrwxrwx 1 root root 90, 16 May 30 2007 /dev/mtd8
crwxrwxrwx 1 root root 90, 18 May 30 2007 /dev/mtd9
# ls /dev/mtdblock? -l
brw-r—– 1 root root 31, 0 May 30 2007 /dev/mtdblock0
brw-r—– 1 root root 31, 1 May 30 2007 /dev/mtdblock1
brw-r—– 1 root root 31, 2 May 30 2007 /dev/mtdblock2
brw-r—– 1 root root 31, 3 May 30 2007 /dev/mtdblock3
brwxrwxrwx 1 root root 31, 4 May 30 2007 /dev/mtdblock4
brwxrwxrwx 1 root root 31, 5 May 30 2007 /dev/mtdblock5
brwxrwxrwx 1 root root 31, 6 May 30 2007 /dev/mtdblock6
brwxrwxrwx 1 root root 31, 7 May 30 2007 /dev/mtdblock7
brwxrwxrwx 1 root root 31, 8 May 30 2007 /dev/mtdblock8
brwxrwxrwx 1 root root 31, 9 May 30 2007 /dev/mtdblock9
此设备号，定义在/include/linux/mtd/mtd.h中 ：
#define MTD_CHAR_MAJOR 90
#define MTD_BLOCK_MAJOR 31
3. 其中，mtd的块设备的大小，可以通过查看分区信息获得：
# cat /proc/partitions
major minor #blocks name
31 0 1024 mtdblock0
31 1 8192 mtdblock1
31 2 204800 mtdblock2
31 3 65536 mtdblock3
31 4 225280 mtdblock4
上面中显示的块设备大小，是block的数目，每个block是1KB。
而每个字符设备，其实就是对应着上面的每个块设备。即/dev/mtd0对应/dev/mtdblock0，其他以此类推。换句话说，mtdblockN的一些属性，也就是mtdN的属性，比如大小。
4。对每个mtd字符设备的操作，比如利用nandwrite去对/dev/mtd0写数据，实际就是操作/dev/mtdblock0。
而这些操作里面涉及到的偏移量offset，都指的是此mtd 分区内的偏移。比如向/dev/mtd1的offset为0的位置写入数据，实际操作的是物理偏移offset=/dev/mtd0的大小=1MB=0×100000。
5.mtd的字符设备和块设备的命名规则，可以参考下表：
Table 7-1. MTD /dev entries, corresponding MTD user modules, and relevant device major numbers
| /dev entry | Accessible MTD user module | Device type | Major number |
|---|---|---|---|
| mtdN | char device | char | 90 |
| mtdrN | char device | char | 90 |
| mtdblockN | block device, read-only block device, JFFS, and JFFS2 | block | 31 |
| nftlLN | NFTL | block | 93 |
| ftlLN | FTL | block | 44 |
Table 7-2. MTD /dev entries, minor numbers, and naming schemes
| /dev entry | Minor number range | Naming scheme |
|---|---|---|
| mtdN | 0 to 32 per increments of 2 | N = minor / 2 |
| mtdrN | 1 to 33 per increments of 2 | N = (minor – 1) / 2 |
| mtdblockN | 0 to 16 per increments of 1 | N = minor |
| nftlLN | 0 to 255 per sets of 16 | L = set;[2]N = minor – (set – 1) x 16; N is not appended to entry name if its value is zero. |
| ftlLN | 0 to 255 per sets of 16 | Same as NFTL. |
上表相关内容，请参考附录2.
【附录】
1.最新的mtd-utils-1.3.0.tar.bz2 下载地址：ftp://ftp.infradead.org/pub/mtd-utils/mtd-utils-1.3.0.tar.bz2
2.7.1 MTD-Supported Devices
http://book.opensourceproject.org.cn/embedded/oreillybuildembed/opensource/belinuxsys-chp-7-sect-1.html
