Re: [PATCH for-4.2? v3 0/8] block: Fix resize (extending) of short overlays

[Kevin Wolf <kwolf@redhat.com>]

Am 19.12.2019 um 10:24 hat Vladimir Sementsov-Ogievskiy geschrieben:
> 10.12.2019 20:46, Kevin Wolf wrote:
> > Am 22.11.2019 um 17:05 hat Kevin Wolf geschrieben:
> >> See patch 4 for the description of the bug fixed.
> > 
> > I'm applying patches 3 and 5-7 to the block branch because they make
> > sense on their own.
> > 
> > The real fix will need another approach because the error handling is
> > broken in this one: If zeroing out fails (either because of NO_FALLBACK
> > or because of some other I/O error), bdrv_co_truncate() will return
> > failure, but the image size has already been increased, with potentially
> > incorrect data in the new area.
> > 
> > To fix this, we need to make sure that zeros will be read before we
> > commit the new image size to the image file (e.g. qcow2 header) and to
> > bs->total_sectors. In other words, it must become the responsibility of
> > the block driver.
> > 
> > To this effect, I'm planning to introduce a PREALLOC_MODE_ZERO_INIT flag
> > that can be or'ed to the preallocation mode. This will fail by default
> > because it looks like just another unimplemented preallocation mode to
> > block drivers. It will be requested explicitly by commit jobs and
> > automatically added by bdrv_co_truncate() if the backing file would
> > become visible (like in this series, but now for all preallocation
> > modes). I'm planning to implement it for qcow2 and file-posix for now,
> > which should cover most interesting cases.
> > 
> > Does this make sense to you?
> 
> This should work. Do you still have this plan in a timeline?

Still planning to do this, but tomorrow is my last working day for this
year. So I guess I'll get to it sometime in January.

Kevin