The assertion failure mentioned in the bug has been addressed.  QEMU still cannot launch a guest where the disk is offline (returns -EIO).

This clone is for making QEMU capable of starting with an offline disk.


+++ This bug was initially created as a clone of Bug #1184363 +++

Description of problem:
     It is not possible to start a VM which has a failed multipath device connected.


Version-Release number of selected component (if applicable):
     qemu-kvm-1.5.3-60.el7_0.11

How reproducible:
     100%

Steps to Reproduce:
1. Create a VM and a multipath device as a disk:

    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native'/>
      <source dev='/dev/mapper/3600140519ce508030c64008be5be247d'/>
      <target dev='vdb' bus='virtio'/>
      <boot order='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
    </disk>

2. Mark all the paths of the mulitpath device as failed:
    # multipath -ll
      ...
          3600140519ce508030c64008be5be247d dm-12 LIO-ORG ,iscsi17         
          size=10G features='0' hwhandler='0' wp=rw
          `-+- policy='service-time 0' prio=1 status=active
            `- 7:0:0:16 sds 65:32 failed ready  running

    # multipathd -c fail path sds

    # multipath -ll
      ...
          3600140519ce508030c64008be5be247d dm-12 LIO-ORG ,iscsi17         
          size=10G features='0' hwhandler='0' wp=rw
          `-+- policy='service-time 0' prio=1 status=enabled
            `- 7:0:0:16 sds 65:32 failed ready  running

3. Start the VM

Actual results:
error: Failed to start domain Host_boot_test
error: internal error: early end of file from monitor: possible problem:
Warning: option deprecated, use lost_tick_policy property of kvm-pit instead.
qemu-kvm: block.c:849: bdrv_open_common: Assertion `bdrv_opt_mem_align(bs) != 0' failed.


Expected results:
VM is started

--- Additional comment from Stefan Hajnoczi on 2015-01-21 07:45:29 EST ---

(In reply to Roman Hodain from comment #0)
> Description of problem:
>      It is not possible to start a VM which has a failed multipath device
> connected.
...
> Actual results:
> error: Failed to start domain Host_boot_test
> error: internal error: early end of file from monitor: possible problem:
> Warning: option deprecated, use lost_tick_policy property of kvm-pit instead.
> qemu-kvm: block.c:849: bdrv_open_common: Assertion `bdrv_opt_mem_align(bs)
> != 0' failed.

The multipath device fails all I/O requests so QEMU is unable to probe the O_DIRECT memory and request alignment by attempting reads on the device.

Regarding the expected behavior, do you want the VM to start but all I/Os will return errors until the path comes online again?

--- Additional comment from Roman Hodain on 2015-01-23 05:43:20 EST ---

(In reply to Stefan Hajnoczi from comment #1)
> (In reply to Roman Hodain from comment #0)
> > Description of problem:
> >      It is not possible to start a VM which has a failed multipath device
> > connected.
> ...
> > Actual results:
> > error: Failed to start domain Host_boot_test
> > error: internal error: early end of file from monitor: possible problem:
> > Warning: option deprecated, use lost_tick_policy property of kvm-pit instead.
> > qemu-kvm: block.c:849: bdrv_open_common: Assertion `bdrv_opt_mem_align(bs)
> > != 0' failed.
> 
> The multipath device fails all I/O requests so QEMU is unable to probe the
> O_DIRECT memory and request alignment by attempting reads on the device.
> 
> Regarding the expected behavior, do you want the VM to start but all I/Os
> will return errors until the path comes online again?

Hi,

yes, the use case here is disaster recovery where the VM has two mirrored LUNs connected and one of them is down and this prevents the VM from starting even the second LUN is available and the VM would be able to start. 

Roman

--- Additional comment from Stefan Hajnoczi on 2015-02-19 09:16:11 EST ---

This bug can be reproduced with:

$ echo "0 $((8 * 1024 * 1024 * 1024 / 512)) error" | sudo dmsetup create eiodev
$ qemu-system-x86_64 -enable-kvm \
                     -drive if=virtio,file=/dev/mapper/eiodev,cache=none
qemu-system-x86_64: block.c:860: bdrv_open_common: Assertion `bdrv_opt_mem_align(bs) != 0' failed.

(Use "dmsetup remove eiodev" to clean up after the test.)

I have backported the error message from upstream.  This prevents an assertion failure but does not support starting QEMU with failed disks yet:

qemu-system-x86_64: -drive if=none,file=/dev/mapper/eiodev,cache.direct=on,id=drive0: could not open disk image /dev/mapper/eiodev: Could not find working O_DIRECT alignment. Try cache.direct=off.