[libvirt] [PATCH v2] snapshot: fix rollback failure in transaction mode

[Eric Blake]

On 09/13/2012 03:41 AM, Guannan Ren wrote:
> BZ:https://bugzilla.redhat.com/show_bug.cgi?id=843372
> 
> when qemu supports the 'transaction' monitor command,
> and libvirt's --reuse-ext flag was not specified, libvirt created
> a stub file with zero size in first place. After the failure of
> QEMU transaction command performing qcow2 snapshots on more than
> one drives, the stub file is left behind with non-empty
> by the QEMU transaction command.
> 
> In order to unlink the file, the patch removes the file size checking.

I was still hoping you'd list the reproduction steps here in the commit
message, rather than making me chase down a link.  Remember, a year down
the road, when reading 'git log', the more self-contained the log is,
the easier it will be to understand WHY the patch is appropriate.

Conditional ACK - no need to post a v3; I'm okay if you push once you
amend the commit message.  Keep the mention of the BZ number, but also
add this text (from your previous message).

     qemu left non-empty file.
     Steps:
     1, Create a qemu instance with two drive images of qcow2 type (root
user)
          /usr/libexec/qemu-kvm -m 1024 -smp 1 -name "rhel6u1" \
           -drive
file=/var/lib/libvirt/images/firstqcow2,if=none,id=drive-virtio-disk0,format=qcow2,cache=none
           -device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
\
           -drive
file=/var/lib/libvirt/images/secondqcow2,if=none,id=drive-virtio-disk1,format=qcow2,cache=none
\
           -device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=drive-virtio-disk1,id=virtio-disk1
-qmp stdio

     2, Initialize qemu qmp
         {"execute":"qmp_capabilities"}

     3, Remove the second drive image file
         rm -f /var/lib/libvirt/images/secondqcow2

     4, Run 'transaction' command with snapshot qemu commands in.
         {"execute":"transaction","arguments":
           {"actions":
[{"type":"blockdev-snapshot-sync","data":{"device":"drive-virtio-disk0","snapshot-file":"/var/lib/libvirt/images/firstqcow2-snapshot.img","format":"qcow2"}},
{"type":"blockdev-snapshot-sync","data":{"device":"drive-virtio-disk1","snapshot-file":"/var/lib/libvirt/images/secondqcow2-snapshot.img","format":"qcow2"}}]
           },
         "id":"libvirt-6"}

     5,  Got the error as follows:
         {"id": "libvirt-6", "error": {"class": "OpenFileFailed",
"desc": "Could not open '/var/lib/libvirt/images/secondqcow2-snapshot.img'",
                                  "data": {"filename":
"/var/lib/libvirt/images/secondqcow2-snapshot.img"}}}

     6, List first newly-created snapshot file:
         -rw-r--r--. 1 root root     262144 Sep 13 11:43
firstqcow2-snapshot.img

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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