Re: [Qemu-devel] [PATCH v2 1/5] qapi/block: Add "fatal" to BLOCK_IMAGE_CORRUPTED

[Max Reitz <mreitz@redhat.com>]

On 05.09.2014 16:40, Eric Blake wrote:
> On 09/05/2014 08:07 AM, Max Reitz wrote:
>> Not every BLOCK_IMAGE_CORRUPTED event must be fatal; for example, when
>> reading from an image, they should generally not be. Nonetheless, even
>> an image only read from may of course be corrupted and this can be
>> detected during normal operation. In this case, a non-fatal event should
>> be emitted, but the image should not be marked corrupt (in accordance to
>> "fatal" set to false).
>>
> Question - what happens if management misses the signal?  For example,
> if libvirt opens qemu on a read-only image, then goes away, then
> corruption is detected, then libvirt reconnects.  Does query-block need
> to also be updated to report whether a read-only BDS is currently
> detected as fatal, but that an event has already been delivered?

Well, the obvious problem with that is that corruption currently is a 
strongly format-specific topic, and only reported for qcow2. So, to do 
this, we'd have to move the corruption signalling code into the common 
block layer functions and proceed from there. This actually probably 
isn't too bad of an idea, anyway. But then we'll need a global 
bdrv_mark_corrupt() function (which we probably don't want in case we 
get more flags in the future, so we'll rather want bdrv_set_flag() or 
something) and I don't really want to make these changes now... We could 
postpone this, though. Making this change later shouldn't break anything.

The other solution would be simply to suppress the stderr message but to 
always deliver the QMP event.

Max