Re: [PATCH] block/io: fallback to bounce buffer if BLKZEROOUT is not supported because of alignment

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Jan 05, 2026 at 03:29:55PM +0100, Fiona Ebner wrote:
> 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.
> Fallback to the bounce buffer, similar to when the ioctl is not
> supported at all, rather than treating such an error as fatal.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3257
> Resolves: https://bugzilla.proxmox.com/show_bug.cgi?id=7197
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
>  block/io.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Thanks, applied to my block tree with a TODO comment about
taking the write_zeroes_alignment limit into account:
https://gitlab.com/stefanha/qemu/commits/block

Stefan

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