Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking

[Paolo Bonzini]

Il 06/03/2013 18:50, Peter Lieven ha scritto:
>> > Commit 9a665b2b made bdrv_truncate() call bdrv_drain_all(), but this breaks
>> > QCOW images, as well other future image formats (such as VHDX) that may 
>> > call
>> > bdrv_truncate(bs->file) from within a read/write operation.  For example, 
>> > QCOW
>> > will cause an assert, due to tracked_requests not being empty (since the
>> > read/write that called bdrv_truncate() is still in progress).

I'm not sure such bdrv_truncate calls are necessary.  QCOW2 doesn't have
them (almost; there is one in qcow2_write_compressed, I'm not even sure
that one is necessary though), and I think QCOW's breaks using it with a
block device as a backing file.

Paolo