Re: [Qemu-block] [Qemu-devel] [PATCH v4 0/3] block: Fix unaligned bdrv_aio_write_zeroes

[Fam Zheng]

On Mon, 04/27 15:23, Paolo Bonzini wrote:
> 
> 
> On 27/04/2015 15:18, Fam Zheng wrote:
> > An unaligned zero write causes NULL deferencing in bdrv_co_do_pwritev. That
> > path is reachable from bdrv_co_write_zeroes and bdrv_aio_write_zeroes.
> > 
> > You can easily trigger through the former with qemu-io, as the test case 
> > added
> > by 61815d6e0aa. For bdrv_aio_write_zeroes, in common cases there's always a
> > format driver (which uses 512 alignment), so it would be much rarer to have
> > unaligned requests (only concerning top level here, when the request goes 
> > down
> > to bs->file, where for example the alignment is 4k, it would then be calling
> > bdrv_co_write_zeroes because it's in a coroutine).
> > 
> > fc3959e4669a1c fixed bdrv_co_write_zeroes but not bdrv_aio_write_zeroes.  
> > The
> > lattern is the actually used one by device model. Revert the previous fix, 
> > do
> > it in bdrv_co_do_pwritev, to cover both paths.
> > 
> > v4: "if (!qiov)" -> "if (!qiov && bytes >= align)". (Paolo)
> > 
> > v3: Fix the case where the unaligned request is contained within the first
> >     block. (Paolo)
> >     Also update iotests 033 to cover the code path with qemu-io.
> > 
> > v2: Split to three aligned pwritev.
> > 
> > 
> > Fam Zheng (3):
> >   Revert "block: Fix unaligned zero write"
> >   block: Fix NULL deference for unaligned write if qiov is NULL
> >   qemu-iotests: Test unaligned sub-block zero write
> > 
> >  block.c                    | 123 
> > +++++++++++++++++++++++++--------------------
> >  tests/qemu-iotests/033     |  13 +++++
> >  tests/qemu-iotests/033.out |  30 +++++++++++
> >  3 files changed, 111 insertions(+), 55 deletions(-)
> > 
> 
> Reviewed-by: Paolo Bonzini <address@hidden>
> 

Thanks very much for your attentive reviewing!

Fam