Re: [Qemu-devel] [PATCH 3/3] virtio-scsi: Forbid devices with different iothreads sharing a blockdev

[Alberto Garcia]

On Mon 28 Jan 2019 03:57:43 PM CET, Kevin Wolf wrote:

>> > I think the proper solution on the block layer level would be that
>> > AioContext is managed per BdrvChild and only BdrvChild objects with
>> > the same AioContext can be attached to the same node.
>> > bdrv_set_aio_context() would then fail if another parent is already
>> > using the node.
>> 
>> How would that solve the virtio-blk problem, though? :-?
>
> It wouldn't, but it would make clear that bdrv_set_aio_context() can
> fail and we'd have to handle the problem exactly there.

Yes, that sound like the proper solution.

> The only other option I see is downgrading to non-dataplane mode, but
> this would have to be silent because during machine reset we have no
> way to report errors.

Yes, I actually had a patch doing that, but as you said the user has no
way of knowing that it went wrong.

If you have 2 or 3 virtio-blk devices with different iothreads using the
same BDS then after the guest reboot only one would succeed, but you
can't see which one, or can you?

Berto