On Thu, May 28, 2026 at 10:32:32AM +0200, Fiona Ebner wrote: > Am 27.05.26 um 11:06 PM schrieb Stefan Hajnoczi: > > On Thu, Feb 5, 2026 at 11:03 AM Kevin Wolf <[email protected]> wrote: > >> > >> Am 05.02.2026 um 13:13 hat Fiona Ebner geschrieben: > >>> 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 didn't review this thoroughly yet, but I agree that considering the > >> alignment from the start is the better solution and also more consistent > >> with what we're already doing for normal reads and writes. > >> > >> We just need to make sure that we use the right alignments in the right > >> places, which can be a bit confusing with the fallbacks to buffered zero > >> writes here and there. > >> > >> I assume that there is enough time left to do this before the 11.0 > >> release and there is no need to take something like v1 as an > >> intermediate solution? > > > > No progress has been made and I'm unable to commit time at the moment. > > Me neither unfortunately. > > > Is everyone okay with merging Fiona's smaller original patch? While it > > would be nice to implement a deeper fix, it's better to have a fix and > > I think there is no great risk merging the original patch. > > > > https://lore.kernel.org/qemu-devel/[email protected]/ > > FWIW, we have been using that patch downstream since mid-February [0] > and nobody reported issues with it as far as I'm aware. I suppose it > could use a 'TODO' code comment that the proper fix looks different. If > you choose to go with that patch, should I send a v2 with such a comment > or can that be added when applying?
I can add the comment when merging the patch. I will merge it on Monday so Kevin still has some time to reply in case he has an opinion. Stefan > > Best Regards, > Fiona > > [0]: > https://git.proxmox.com/?p=pve-qemu.git;a=commitdiff;h=6960b5e033fa911f9882751950df28a193255683 >
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