GNU/Linux - wic文件的使用

Yocto/OpenEmbedded使用的磁盘镜像格式是 wic。为嵌入式系统提供 bootable images。

The disk image format used in the Yocto Project is wic.

.wic 文件显然只是一个带有分区表和分区的磁盘镜像，就像下载 Linux 发行版时获得的所有 .img 文件一样。这就是为什么你可以使用 dd 命令烧写 .wic 文件，就像使用 .img 文件一样。

A .wic file is apparently just a disk image with a partition table and partitions, just like all the .img files you get when downloading e.g Linux distros. That's why you can flash a .wic file using dd just like you would with a .img file.

之所以使用 .wic 文件扩展名，是因为它是由 wic 工具创建的，该工具读取 .wks 文件中描述的分区布局，并生成带有相应分区的映像。有关 wic 工具的更多信息，请参阅： 19 Creating Partitioned Images Using Wic — The Yocto Project ® 5.0.1 documentation

The reason for the .wic file extension is simply that it's created by the wic tool, which reads a partition layout described in a .wks file and generates an image with the corresponding partitions. For more info on the wic tool, see:  19 Creating Partitioned Images Using Wic — The Yocto Project ® 5.0.1 documentation 

如何读取wic文件中的内容呢？

1，Mount the .wic File

将wic文件加载为loop device。

Automatically find an available loop device and associate it with a file.

$ sudo losetup -Pf --show my-image.wic

/dev/loop17

$ losetup --help

-a, --all                     list all used devices

-P, --partscan                create a partitioned loop device

-f, --find                    find first unused device

--show                    print device name after setup (with -f)

-d, --detach <loopdev>...     detach one or more devices

-D, --detach-all              detach all used devices

$ losetup -a

上面结果显示加载为/dev/loop17设备。

将设备名赋值给变量：

LOOP_DEVICE=$(sudo losetup -Pf --show my-image.wic)

2, List Partitions

使用fdisk命令，查看加载设备的分区信息

$ sudo fdisk -l /dev/loop17

Disk /dev/loop17: 7.11 GiB, 7638816768 bytes, 14919564 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: 0x076c4a2a

Device        Boot  Start      End  Sectors  Size Id Type

/dev/loop17p1 *     16384   186775   170392 83.2M  c W95 FAT32 (LBA)

/dev/loop17p2      196608 14919563 14722956    7G 83 Linux

3，Mount Partitions

sudo mount  /dev/loop17p1 mnt

4，Access Files

cd mnt

ls

5, Cleaning up

Unmount partitions:

sudo umount mnt

6, Detach the loop device

sudo losetup -d /dev/loop17

---

使用kpartx命令操作：

$ kpartx --help

-a add partition devmappings

-d del partition devmappings

-v verbose

-l list partitions devmappings that would be added by -a

$ sudo kpartx -av my-image.wic

[sudo] password for dev:

add map loop17p1 (252:0): 0 170392 linear 7:17 16384

add map loop17p2 (252:1): 0 14722956 linear 7:17 196608

$ sudo kpartx -l my-image.wic

loop17p1 : 0 170392 /dev/loop17 16384

loop17p2 : 0 14722956 /dev/loop17 196608

$ sudo kpartx -l /dev/loop17

loop17p1 : 0 170392 /dev/loop17 16384

loop17p2 : 0 14722956 /dev/loop17 196608

$ sudo fdisk -l /dev/loop17

Disk /dev/loop17: 7.11 GiB, 7638816768 bytes, 14919564 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: 0x076c4a2a

Device        Boot  Start      End  Sectors  Size Id Type

/dev/loop17p1 *     16384   186775   170392 83.2M  c W95 FAT32 (LBA)

/dev/loop17p2      196608 14919563 14722956    7G 83 Linux

$ ls /dev/mapper/

control  loop17p1  loop17p2

$ sudo mount /dev/mapper/loop17p2 mnt

$ sudo umount mnt

$ sudo kpartx -dv my-image.wic

del devmap : loop17p1

del devmap : loop17p2

loop deleted : /dev/loop17

$ sudo kpartx -dv /dev/loop17

del devmap : loop17p1

del devmap : loop17p2

参考：

linux - Difference between wic and hddimg format in yocto - Stack Overflow