EMMC分区（MBR）

一、需求描述

在某些情况下，需要对EMMC快速分区，可以通过只写分区头的方式来实现。

对MBR格式的分区，通常分区头都在第一个Sector扇区。我们只需要将已经分好区的镜像或者linux下分区对应的的块设备的前512个字节读取出来保存，下次分区直接导入即可完成分区。

二、实现过程

2.1 导出分区头

dd if=/dev/mmcblk0 of=p0partition2.bin bs=512 count=1

查看内容：

fudiboardnodp:/home/petalinux# hexdump -Cv p0partition2.bin

00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000080 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

000000a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

000000b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

000000c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

000000d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

000000e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

000000f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000110 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000120 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000130 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000140 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000150 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000160 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000170 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000180 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

00000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

000001a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

000001b0 00 00 00 00 00 00 00 00 9e 69 83 a0 00 00 00 00 |.........i......|

000001c0 01 20 83 03 10 1f 00 08 00 00 00 00 10 00 00 00 |. ..............|

000001d0 01 20 83 03 90 1f 00 08 10 00 00 80 00 00 00 00 |. ..............|

000001e0 81 20 83 03 10 1f 00 88 10 00 00 80 00 00 00 00 |. ..............|

000001f0 01 20 05 03 d0 ff 00 08 11 00 00 f8 d7 00 55 aa |. ............U.|

00000200

2.2 通过导入分区表实现分区

dd if=p0partition2.bin of=/dev/mmcblk0 bs=512 count=1

2.3 实现效果

/home/petalinux# fdisk /dev/mmcblk0

Welcome to fdisk (util-linux 2.37.2).

Changes will remain in memory only, until you decide to write them.

Be careful before using the write command.

Command (m for help): p

Disk /dev/mmcblk0: 7.28 GiB, 7818182656 bytes, 15269888 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disklabel type: dos

Disk identifier: 0xa083699e

Device Boot Start End Sectors Size Id Type

/dev/mmcblk0p1 2048 1050623 1048576 512M 83 Linux

/dev/mmcblk0p2 1050624 1083391 32768 16M 83 Linux

/dev/mmcblk0p3 1083392 1116159 32768 16M 83 Linux

/dev/mmcblk0p4 1116160 15269887 14153728 6.7G 5 Extended

/dev/mmcblk0p5 1118208 1642495 524288 256M 83 Linux

/dev/mmcblk0p6 1644544 1677311 32768 16M 83 Linux

2.4 常用命令

2.4.1 删除所有分区

nodp:/home/petalinux# fdisk /dev/mmcblk0

Welcome to fdisk (util-linux 2.37.2).

Changes will remain in memory only, until you decide to write them.

Be careful before using the write command.

Command (m for help): p

Disk /dev/mmcblk0: 7.28 GiB, 7818182656 bytes, 15269888 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disklabel type: dos

Disk identifier: 0xa083699e

Device Boot Start End Sectors Size Id Type

/dev/mmcblk0p1 2048 1050623 1048576 512M 83 Linux

/dev/mmcblk0p2 1050624 1083391 32768 16M 83 Linux

/dev/mmcblk0p3 1083392 1116159 32768 16M 83 Linux

/dev/mmcblk0p4 1116160 15269887 14153728 6.7G 5 Extended

/dev/mmcblk0p5 1118208 1642495 524288 256M 83 Linux

/dev/mmcblk0p6 1644544 1677311 32768 16M 83 Linux

Command (m for help): o

Created a new DOS disklabel with disk identifier 0x210b2e2b.

Command (m for help): p

Disk /dev/mmcblk0: 7.28 GiB, 7818182656 bytes, 15269888 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disklabel type: dos

Disk identifier: 0x210b2e2b

2.4.2 格式化所有分区数据

上面命令只是删除了分区表，但是分区中的数据还是存在的，如果需要清除分区数据的话，需要使用下面命令：

dd if=/dev/zero of=/dev/mmcblk0 bs=512 count=1