On Thu, Feb 05, 2026 at 01:13:57PM +0100, Fiona Ebner wrote: > Hi Stefan, > > Am 02.02.26 um 11:15 PM schrieb Stefan Hajnoczi: > > On Fri, Jan 09, 2026 at 01:08:27PM +0100, Fiona Ebner wrote: > >> Previous discussion here: > >> https://lore.kernel.org/qemu-devel/[email protected]/ > >> > >> Commit 5634622bcb ("file-posix: allow BLKZEROOUT with -t writeback") > >> enables the BLKZEROOUT ioctl when using 'writeback' cache, regressing > >> certain 'qemu-img convert' invocations, because of a pre-existing > >> issue. Namely, the BLKZEROOUT ioctl might fail with errno EINVAL when > >> the request is shorter than the block size of the block device. > >> > >> Stefan suggested prioritizing bl.pwrite_zeroes_alignment in > >> bdrv_co_do_zero_pwritev(). This RFC explores that approach and the > >> issues with qcow2 I encountered, where > >> bl.pwrite_zeroes_alignment = s->subcluster_size; > >> I would be happy to discuss potential solutions and whether we should > >> use this approach after all. > > > > Hi Fiona, > > I wanted to continue this discussion. My thoughts are that making > > bdrv_co_do_zero_pwritev() use bl.pwrite_zeroes_alignment is the right > > long-term solution to keep all the padding logic in one place. > > > > On the other hand, your series shows it involves fixing a bunch of test > > failures and that's not fun. The original bug that is being solved here > > is my doing, so feel free to hand this over to me if you decide you > > don't want to work on it. > > in your other mail, you mentioned you'll ask Kevin for his opinion. So > in part, I was waiting for that. But I also was side-tracked by other > things, and it will be 1-2 more weeks until I can really focus on this > again. If that is too long, please go ahead and pick it up.
I have pinged him now. My timeframe is similar. I can look into this as a background task and if I make progress I'll share it with you. Stefan
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