CODEWITHSUNDEEP
libvirtmount-point
coanor
coanor

Reputation: 3954

qemu: how to get image UUID

I want to mount a existing image (file.vhd) to a running guest:

<!-- attach.xml -->
<disk type='file' device='disk'>
    <driver name='qemu' type='vpc' cache='none' io='native' dataplane='on' />
    <source file='/path/to/file.vhd'/>
    <target dev='vdf'/>
</disk>

then

# virsh attach-device guest1 attach.xml

here, I want to mount file.vhd to guest1 and under /dev/vdf, but when there is only two device existed on guest1, file.vhd will mount to /dev/vdc (/dev/vda and /dev/vbd has been occupied by existing 2 disk), so I can't know where file.vhd will be mounted without login into guest1 for checking.

How to make it possible to know the mount point before I mount file.vhd?

By the way, at the same time, there may be other client attach some.vhd to guest1, so just check the next mount point on guest1 remotely may not work.

I know the lsblk can list device's UUID like this:

# lsblk -nio NAME,UUID

I don't know if the UUID is existed within the file.vhd before I attached to guest1 or only generated by guest1. If the UUID is existed within file.vhd, how to get it?

I have tried mount the same file.vhd file to guest1 multiple times (with different /dev/vd*), it seems that the UUID of them are the same, so I think the UUID may existed within file.vhd, but I still not sure definitely.

Upvotes: 1

Views: 7888

Answers (1)

DanielB
DanielB

Reputation: 2816

libguestfs provides a set of tools for manipulating / inspecting disk images. This is capable of reporting the label & UUID associated with any filesystems inside a guest disk image. e.g. http://libguestfs.org/virt-filesystems.1.html

 $ virt-filesystems -a win.img --all --long --uuid -h
 Name      Type       VFS  Label           Size Parent   UUID
 /dev/sda1 filesystem ntfs System Reserved 100M -        F81C92571C92112C
 /dev/sda2 filesystem ntfs -               20G  -        F2E8996AE8992E3B
 /dev/sda1 partition  -    -               100M /dev/sda -
 /dev/sda2 partition  -    -               20G  /dev/sda -
 /dev/sda  device     -    -               20G  -        -

A possibly simpler alternative to this though (particularly if you just have a single partition in the disk), is to specify a unique serial string in the disk XML e.g.

<disk type='file' device='disk'>
    <driver name='qemu' type='vpc' cache='none' io='native' dataplane='on' />
    <source file='/path/to/file.vhd'/>
    <serial>XXXXXXXXXX</serial>
    <target dev='vdf'/>
</disk>

The text in the serial field gets included in the /dev/disk/by-path symlinks, allowing you to have a predictable device name to mount it with.

Upvotes: 3

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