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Date: Wed, 01 Aug 2012 13:45:03 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 14/47] stream: add on-error argument
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: jcody@redhat.com, eblake@redhat.com, qemu-devel@nongnu.org, stefanha@linux.vnet.ibm.com

Am 01.08.2012 13:11, schrieb Paolo Bonzini:
> Il 01/08/2012 12:29, Kevin Wolf ha scritto:
>>>> +    if ((on_error == BLOCKDEV_ON_ERROR_STOP ||
>>>> +         on_error == BLOCKDEV_ON_ERROR_ENOSPC) &&
>>>> +        !bdrv_iostatus_is_enabled(bs)) {
>>>> +        error_set(errp, QERR_INVALID_PARAMETER, "on-error");
>>>> +        return;
>>>> +    }
>> Hm, this is an interesting one. bdrv_iostatus_is_enabled() returns true
>> for a block device that is (or was once) attached to virtio-blk, IDE or
>> scsi-disk. Which made sense so far because only these devices would
>> actually set the status.
>>
>> Now with block jobs, we have other places that can set the status. And
>> we have images that don't belong to any device, but can still get errors
>> (mirror target). Maybe it would make sense to just enable the iostatus
>> here instead of failing?
> 
> I'm not sure what would happen, so I preferred to be safe.
> 
> The right solution would be "support iostatus in sd and friends, and
> drop bdrv_iostatus_is_enabled altogether", of course...

Support it _for_ sd and friends, but support it _in_ the block layer.
What's missing before this can happen is a VMState for the block layer
so that requeued requests can be migrated. Breaks migration
compatibility, obviously.

Kevin