Re: [Qemu-devel] [patch] Fix block I/O hang.

[Gerd Hoffmann <kraxel@redhat.com>]

Anthony Liguori wrote:
> Gerd Hoffmann wrote:
>>  
>>> Under what circumstances?  posix_aio_read() is only invoked from a
>>> select callback.  This means there should be data available to be read.
>>>     
>>
>> Well, there are *two* select loops:  main_loop_wait() and
>> qemu_aio_wait().  Calling sync block i/o functions from a i/o handler
>> causes the two select loops run nested => boom.
> 
> Yeah, qemu_aio_wait needs to die.  Can you resubmit your patch with a
> better description, and change the read() look in posix_aio_read() to
> consume as much data as possible before hitting EAGAIN?

I've fixed my problem by changing xen_disk to use a bottom half for
actual work, so the block read/write calls are moved out of the select
loop anyway.  Which turned out to be useful for aio support too.

So I'm fine again with the current state.  I can create such a patch
nevertheless though.

cheers,
  Gerd