On Fri, May 31, 2013 at 3:55 PM, Richard W.M. Jones <rjones@redhat.com> wrote:

On Fri, May 31, 2013 at 10:58:30AM +0800, Qiu Yu wrote:
> Unfortunately, the standard 'disk' group permission only applies to
> /dev/sdX device nodes, not to device mapper nodes created by LVM commands.

Actually, it depends on udev rules. On my machine device mapper
nodes very much are owned by the disk group:

$ ll /dev/dm-*
brw-rw----. 1 root disk 253, 0 May 15 13:26 /dev/dm-0
brw-rw----. 1 root disk 253, 1 May 15 13:26 /dev/dm-1
brw-rw----. 1 root disk 253, 10 May 24 13:54 /dev/dm-10
brw-rw----. 1 root disk 253, 11 May 15 13:26 /dev/dm-11
brw-rw----. 1 root root 253, 12 May 29 21:29 /dev/dm-12
[etc]

You can add udev rules to change the ownership. See:

https://wiki.archlinux.org/index.php/Udev

Rich.

Thanks Richard, you're right. I just find out myself few moments ago.

Actually I'm looking into an issue with OpenStack / Libvirt manipulating LVM as an image backend. When the logical volume is created, udev rules will set the ownership to root:disk. After libvirt actually starting an instance, device node ownership will change to qemu:qemu by libvirt. Then, if you stop an instance, the device node ownership will change back to root:root. Seems there's some inconsistency here.

Anyway, it has nothing to do with the libguestfs. Thank you so much for your help and the information! :)

Qiu Yu