[Libguestfs] Libguestfs can't launch with one of the disk images in the RHEV cluster

Tue Jan 14 14:57:35 UTC 2014

-----Original Message-----
From: Richard W.M. Jones [mailto:rjones at redhat.com]
Sent: Tuesday, January 14, 2014 4:42 PM
To: Исаев Виталий Анатольевич
Cc: libguestfs at 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 at rhevh1 mapper]# pwd
/dev/mapper
[root at 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 at 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 at 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 at rhevh1 mapper]# qemu-img info /dev/dm-19
image: /dev/dm-19
file format: raw
virtual size: 40G (42949672960 bytes)
disk size: 0
[root at 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
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