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. Best Regards, Fiona
