[Libguestfs] How to use libguestfs access LVM as non-root user?

[Qiu Yu]

On Fri, May 31, 2013 at 4:17 PM, Richard W.M. Jones <rjones at redhat.com>wrote:

> On Fri, May 31, 2013 at 04:03:32PM +0800, Qiu Yu wrote:
> > 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.
>
> This is actually a well-known bug in libvirt.
>
> https://bugzilla.redhat.com/show_bug.cgi?id=796072
> (marked as a duplicate of a private bug 547546 for some reason --
> I will try to get this made non-private)
>
> You can turn off libvirt's ownership management (set dynamic_ownership
> = 0 in /etc/libvirt/qemu.conf) however this will cause other problems.
> I don't think there is a proper solution to this yet.
>
> Rich.
>
>
Richard,

Really thanks for the advice. But seems I'm hitting another permission
issue regarding libguestfs and LVM image.

Following code snippet is stripped from OpenStack data injection logic.
Running as non-root user (stack) will report "guestfs_launch failed" error,
and the debug message shows it failed to open the LVM device node.

I've already set up the group permission ('disk' and 'fuse') for the
'stack' user. Could you shed some lights of what else should I look into?
Thanks!

$ cat test.py
import guestfs
g = guestfs.GuestFS()
g.add_drive_opts("/dev/xenvg/123", format="qcow2")
g.launch()

$ id
uid=501(stack) gid=504(stack) groups=504(stack),6(disk),498(fuse)

$ ll /dev/mapper/xenvg-123
lrwxrwxrwx 1 root root 7 May 31 17:16 /dev/mapper/xenvg-123 -> ../dm-2
$ ll /dev/dm-2
brw-rw---- 1 root disk 253, 2 May 31 18:06 /dev/dm-2

$ python test.py
libguestfs: trace: add_drive_opts "/dev/xenvg/123" "format:qcow2"
libguestfs: trace: add_drive_opts = 0
libguestfs: trace: launch
libguestfs: trace: launch = -1 (error)
Traceback (most recent call last):
  File "test.py", line 4, in <module>
    g.launch()
  File "/usr/lib/python2.6/site-packages/guestfs.py", line 244, in launch
    return libguestfsmod.launch (self._o)
RuntimeError: guestfs_launch failed, see earlier error messages
libguestfs: trace: close

$ export LIBGUESTFS_DEBUG=1
$ python test.py
libguestfs: new guestfs handle 0x26a8250
libguestfs: trace: add_drive_opts "/dev/xenvg/123" "format:qcow2"
libguestfs: trace: add_drive_opts = 0
libguestfs: trace: launch
libguestfs: [00000ms] febootstrap-supermin-helper --verbose -f checksum
'/usr/lib64/guestfs/supermin.d' x86_64
supermin helper [00000ms] whitelist = (not specified), host_cpu = x86_64,
kernel = (null), initrd = (null), appliance = (null)
supermin helper [00000ms] inputs[0] = /usr/lib64/guestfs/supermin.d
checking modpath /lib/modules/2.6.32-358.6.2.ns8.el6.x86_64 is a directory
picked vmlinuz-2.6.32-358.6.2.ns8.el6.x86_64 because modpath
/lib/modules/2.6.32-358.6.2.ns8.el6.x86_64 exists
supermin helper [00000ms] finished creating kernel
supermin helper [00000ms] visiting /usr/lib64/guestfs/supermin.d
supermin helper [00000ms] visiting /usr/lib64/guestfs/supermin.d/base.img
supermin helper [00000ms] visiting /usr/lib64/guestfs/supermin.d/daemon.img
supermin helper [00000ms] visiting /usr/lib64/guestfs/supermin.d/hostfiles
supermin helper [00015ms] visiting /usr/lib64/guestfs/supermin.d/init.img
supermin helper [00015ms] adding kernel modules
supermin helper [00080ms] finished creating appliance
libguestfs: [00083ms] begin testing qemu features
libguestfs: [00097ms] finished testing qemu features
libguestfs: accept_from_daemon: 0x26a8250 g->state = 1
[00098ms] /usr/libexec/qemu-kvm \
    -global virtio-blk-pci.scsi=off \
    -drive file=/dev/xenvg/123,cache=off,format=qcow2,if=virtio \
    -nodefconfig \
    -enable-kvm \
    -nodefaults \
    -nographic \
    -m 500 \
    -no-reboot \
    -device virtio-serial \
    -serial stdio \
    -chardev socket,path=/tmp/libguestfssaaw6T/guestfsd.sock,id=channel0 \
    -device virtserialport,chardev=channel0,name=org.libguestfs.channel.0 \
    -kernel /var/tmp/.guestfs-501/kernel.30285 \
    -initrd /var/tmp/.guestfs-501/initrd.30285 \
    -append 'panic=1 console=ttyS0 udevtimeout=300 no_timer_check acpi=off
printk.time=1 cgroup_disable=memory selinux=0 guestfs_verbose=1
TERM=screen-bce ' \
    -drive
file=/var/tmp/.guestfs-501/root.30285,snapshot=on,if=virtio,cache=unsafeqemu-kvm:
-drive file=/dev/xenvg/123,cache=off,format=qcow2,if=virtio: could not open
disk image /dev/xenvg/123: Invalid argument
libguestfs: child_cleanup: 0x26a8250: child process died
libguestfs: trace: launch = -1 (error)
Traceback (most recent call last):
  File "test.py", line 4, in <module>
    g.launch()
  File "/usr/lib/python2.6/site-packages/guestfs.py", line 244, in launch
    return libguestfsmod.launch (self._o)
RuntimeError: guestfs_launch failed, see earlier error messages
libguestfs: trace: close
libguestfs: closing guestfs handle 0x26a8250 (state 0)

--
Qiu Yu
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