On Mon 12 Feb 2018 02:14:01 PM CET, Anton Nefedov wrote:
The normal bdrv_co_pwritev() use is either
- BDRV_REQ_ZERO_WRITE clear and iovector provided
- BDRV_REQ_ZERO_WRITE set and iovector == NULL
while
- the flag clear and iovector == NULL is an assertion failure
in bdrv_co_do_zero_pwritev()
- the flag set and iovector provided is in fact allowed
(the flag prevails and zeroes are written)
However the alignment logic does not support the latter case so the
padding areas get overwritten with zeroes.
Oh, so this doesn't simply write zeroes in [offset, offset+bytes), but
also in the head and tail areas, instead of keeping the previous
contents.
This is a pretty serious bug, but I assume it can't be triggered
(bdrv_pwrite_zeroes() is used in complete clusters). Did you check if
there was any other scenario where this could happen?