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? Best Regards, Fiona [0]: https://git.proxmox.com/?p=pve-qemu.git;a=commitdiff;h=6960b5e033fa911f9882751950df28a193255683
