Libguestfs - Jan 2014 - Libguestfs can't launch with one of the disk images in the RHEV cluster

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On Tue, Jan 14, 2014 at 08:07:43AM +0000, Исаев Виталий Анатольевич wrote:
> [00072ms] /usr/libexec/qemu-kvm \
>     -global virtio-blk-pci.scsi=off \
>     -nodefconfig \
>     -nodefaults \
>     -nographic \
>     -drive
file=/dev/mapper/1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da73--4465--aed2--912119fcf67f,snapshot=on,if=virtio
\
>     -nodefconfig \
>     -machine accel=kvm:tcg \
>     -m 500 \
>     -no-reboot \
>     -device virtio-serial \
>     -serial stdio \
>     -device sga \
>     -chardev socket,path=/tmp/libguestfs2yVhoH/guestfsd.sock,id=channel0 \
>     -device virtserialport,chardev=channel0,name=org.libguestfs.channel.0 \
>     -kernel /var/tmp/.guestfs-0/kernel.3269 \
>     -initrd /var/tmp/.guestfs-0/initrd.3269 \
>     -append 'panic=1 console=ttyS0 udevtimeout=300 no_timer_check
acpi=off printk.time=1 cgroup_disable=memory selinux=0 guestfs_verbose=1
TERM=xterm ' \
>     -drive
file=/var/tmp/.guestfs-0/root.3269,snapshot=on,if=virtio,cache=unsafeqemu-kvm:
-drive
file=/dev/mapper/1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da73--4465--aed2--912119fcf67f,snapshot=on,if=virtio:
could not open disk image
/dev/mapper/1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da73--4465--aed2--912119fcf67f:
No such file or directory
> libguestfs: child_cleanup: 0x23dc5d0: child process died
> libguestfs: trace: launch = -1 (error)
libguestfs runs qemu with the command line above.  qemu tries to open
the /dev/mapper/1a9... file.  qemu reports that it cannot open that file.

Unfortunately qemu's error messages are very poor.  However there are
a few possibilities:

(a) An actual permissions issue.  Since you seem to be running this as
root, this doesn't seem to be likely, but you should check that
anyway.  Are there SELinux AVCs?

(b) qemu cannot open the backing file.  Try running:

  qemu-img info /dev/mapper/1a9...

and if it has a backing file, check that the backing file(s)
[recursively] can be opened too.

(c) Also check that the backing file paths are not relative.  If they
are you will need to run your script from the correct directory so
that the relative paths are accessible.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v

-----Original Message-----
From: Richard W.M. Jones [mailto:rjones@redhat.com]
Sent: Tuesday, January 14, 2014 4:42 PM
To: Исаев Виталий Анатольевич
Cc: libguestfs@redhat.com
Subject: Re: [Libguestfs] Libguestfs can't launch with one of the disk
images in the RHEV cluster



On Tue, Jan 14, 2014 at 08:07:43AM +0000, Исаев Виталий Анатольевич wrote:


> [00072ms] /usr/libexec/qemu-kvm \
>     -global virtio-blk-pci.scsi=off \
>     -nodefconfig \
>     -nodefaults \
>     -nographic \
>     -drive
file=/dev/mapper/1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da73--4465--aed2--912119fcf67f,snapshot=on,if=virtio
\
>     -nodefconfig \
>     -machine accel=kvm:tcg \
>     -m 500 \
>     -no-reboot \
>     -device virtio-serial \
>     -serial stdio \
>     -device sga \
>     -chardev socket,path=/tmp/libguestfs2yVhoH/guestfsd.sock,id=channel0 \
>     -device virtserialport,chardev=channel0,name=org.libguestfs.channel.0 \
>     -kernel /var/tmp/.guestfs-0/kernel.3269 \
>     -initrd /var/tmp/.guestfs-0/initrd.3269 \
>     -append 'panic=1 console=ttyS0 udevtimeout=300 no_timer_check
acpi=off printk.time=1 cgroup_disable=memory selinux=0 guestfs_verbose=1
TERM=xterm ' \
>     -drive
> file=/var/tmp/.guestfs-0/root.3269,snapshot=on,if=virtio,cache=unsafeq
> emu-kvm: -drive
> file=/dev/mapper/1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da
> 73--4465--aed2--912119fcf67f,snapshot=on,if=virtio: could not open
> disk image
> /dev/mapper/1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da73--4
> 465--aed2--912119fcf67f: No such file or directory
> libguestfs: child_cleanup: 0x23dc5d0: child process died
> libguestfs: trace: launch = -1 (error)


libguestfs runs qemu with the command line above.  qemu tries to open the
/dev/mapper/1a9... file.  qemu reports that it cannot open that file.



Unfortunately qemu's error messages are very poor.  However there are a few
possibilities:



(a) An actual permissions issue.  Since you seem to be running this as root,
this doesn't seem to be likely, but you should check that anyway.  Are there
SELinux AVCs?



(b) qemu cannot open the backing file.  Try running:



  qemu-img info /dev/mapper/1a9...



and if it has a backing file, check that the backing file(s) [recursively] can
be opened too.



(c) Also check that the backing file paths are not relative.  If they are you
will need to run your script from the correct directory so that the relative
paths are accessible.



Rich.



--

Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines.  Boot with a live CD or
over the network (PXE) and turn machines into KVM guests.

http://libguestfs.org/virt-v2v



Dear Rich, thank you for a prompt reply on my question. The similar problems
have been found with all of the rest Thin Provisioned disks in the cluster,
while all the Preallocated disks were handled with libguestfs correctly. I guess
these issues were caused by (b) and probably (c) reasons:



The backing file of any of the thin provisioned disks does not exist. For
instance let’s consider the
/dev/mapper/1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da73--4465--aed2--912119fcf67f
symbolic link pointing to /dev/dm-30 :
[root@rhevh1 mapper]# pwd
/dev/mapper
[root@rhevh1 mapper]# qemu-img info
1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da73--4465--aed2--912119fcf67f
image:
1a9aa971--f81f--4ad8--932f--607034c924fc-666faa62--da73--4465--aed2--912119fcf67f
file format: qcow2
virtual size: 40G (42949672960 bytes)
disk size: 0
cluster_size: 65536
backing file:
../6439863f-2d4e-48ae-a150-f9054650789c/cbe36298-6397-4ffa-ba8c-5f64e90023e5
[root@rhevh1 mapper]# ll
../6439863f-2d4e-48ae-a150-f9054650789c/cbe36298-6397-4ffa-ba8c-5f64e90023e5
ls: cannot access
../6439863f-2d4e-48ae-a150-f9054650789c/cbe36298-6397-4ffa-ba8c-5f64e90023e5: No
such file or directory

Note that /dev/dm-30 is not accessible with libguestfs.


Now I am trying to find the files with the same name. As a result I receive
three symbolic links pointing to
/dev/1a9aa971-f81f-4ad8-932f-607034c924fc/cbe36298-6397-4ffa-ba8c-5f64e90023e5:
[root@rhevh1 mapper]# find / -name cbe36298-6397-4ffa-ba8c-5f64e90023e5
/dev/1a9aa971-f81f-4ad8-932f-607034c924fc/cbe36298-6397-4ffa-ba8c-5f64e90023e5
/var/lib/stateless/writable/rhev/data-center/mnt/blockSD/1a9aa971-f81f-4ad8-932f-607034c924fc/images/6439863f-2d4e-48ae-a150-f9054650789c/cbe36298-6397-4ffa-ba8c-5f64e90023e5
/rhev/data-center/mnt/blockSD/1a9aa971-f81f-4ad8-932f-607034c924fc/images/6439863f-2d4e-48ae-a150-f9054650789c/cbe36298-6397-4ffa-ba8c-5f64e90023e5

In turn, the
/dev/1a9aa971-f81f-4ad8-932f-607034c924fc/cbe36298-6397-4ffa-ba8c-5f64e90023e5
file is a symbolic link which points to the /dev/dm-19

At last I am trying to launch libguestfs with block device directly:
[root@rhevh1 mapper]# qemu-img info /dev/dm-19
image: /dev/dm-19
file format: raw
virtual size: 40G (42949672960 bytes)
disk size: 0
[root@rhevh1 mapper]# python
Python 2.6.6 (r266:84292, Oct 12 2012, 14:23:48)
[GCC 4.4.6 20120305 (Red Hat 4.4.6-4)] on linux2
Type "help", "copyright", "credits" or
"license" for more information.
>>> import guestfs
>>> g = guestfs.GuestFS()
>>> g.add_drive_opts("/dev/dm-19",readonly=1)
>>> g.launch()
>>> g.lvs()
[]
>>> g.pvs()
[]
>>> g.list_partitions()
['/dev/vda1', '/dev/vda2']
>>> g.inspect_os()
['/dev/vda1']



Now I’m a little bit confused with the results of my research. I found that VM
with the only disk attached has at least two block devices mapped to the
hypervisor’s file system in fact – I mean /dev/dm-19 (raw) and /dev/dm-30
(qcow2). The RHEV-M API (aka Python oVirt SDK) provides no info about the first
one, but the second cannot be accessed from libguestfs.  I have an urgent need
to work with a chosen VM disk images through the libguestfs layer, but I don’t
know which images belong to every VM exactly. It seems like I’m going the hard
way :) Sincerely,



Vitaly Isaev

Software engineer

Information security department

Fintech JSC, Moscow, Russia