[pve-devel] [PATCH qemu 2/2] fix #7197: add fix to avoid misaligned BLKZEROOUT casuing a hard error

[Fiona Ebner <f.ebner@proxmox.com>]

After my initial upstream submission [0], Stefan Hajnoczi suggested a
different approach. But that approach [1] turned out to be rather
involved, some work is still needed and discussion to be had. For now,
pick the initial approach as a stop-gap.

[0]: https://lore.kernel.org/qemu-devel/20260105143416.737482-1-f.ebner@proxmox.com/T/
[1]: https://lore.kernel.org/qemu-devel/20260109120837.2772961-1-f.ebner@proxmox.com/

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 ...k-to-bounce-buffer-if-BLKZEROOUT-is-.patch | 36 +++++++++++++++++++
 debian/patches/series                         |  1 +
 2 files changed, 37 insertions(+)
 create mode 100644 debian/patches/extra/0013-block-io-fallback-to-bounce-buffer-if-BLKZEROOUT-is-.patch

diff --git a/debian/patches/extra/0013-block-io-fallback-to-bounce-buffer-if-BLKZEROOUT-is-.patch b/debian/patches/extra/0013-block-io-fallback-to-bounce-buffer-if-BLKZEROOUT-is-.patch
new file mode 100644
index 0000000..f71f5d2
--- /dev/null
+++ b/debian/patches/extra/0013-block-io-fallback-to-bounce-buffer-if-BLKZEROOUT-is-.patch
@@ -0,0 +1,36 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Fiona Ebner <f.ebner@proxmox.com>
+Date: Mon, 5 Jan 2026 13:36:20 +0100
+Subject: [PATCH] block/io: fallback to bounce buffer if BLKZEROOUT is not
+ supported because of alignment
+
+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(-)
+
+diff --git a/block/io.c b/block/io.c
+index 9bd8ba8431..7b1ad0996a 100644
+--- a/block/io.c
++++ b/block/io.c
+@@ -1917,7 +1917,8 @@ bdrv_co_do_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes,
+             assert(!bs->supported_zero_flags);
+         }
+ 
+-        if (ret == -ENOTSUP && !(flags & BDRV_REQ_NO_FALLBACK)) {
++        if ((ret == -ENOTSUP || (ret == -EINVAL && num < alignment)) &&
++            !(flags & BDRV_REQ_NO_FALLBACK)) {
+             /* Fall back to bounce buffer if write zeroes is unsupported */
+             BdrvRequestFlags write_flags = flags & ~BDRV_REQ_ZERO_WRITE;
+ 
diff --git a/debian/patches/series b/debian/patches/series
index 99d9369..88cfb9b 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -10,6 +10,7 @@ extra/0009-file-posix-populate-pwrite_zeroes_alignment.patch
 extra/0010-block-use-pwrite_zeroes_alignment-when-writing-first.patch
 extra/0011-block-io_uring-avoid-potentially-getting-stuck-after.patch
 extra/0012-block-mirror-check-range-when-setting-zero-bitmap-fo.patch
+extra/0013-block-io-fallback-to-bounce-buffer-if-BLKZEROOUT-is-.patch
 bitmap-mirror/0001-drive-mirror-add-support-for-sync-bitmap-mode-never.patch
 bitmap-mirror/0002-drive-mirror-add-support-for-conditional-and-always-.patch
 bitmap-mirror/0003-mirror-add-check-for-bitmap-mode-without-bitmap.patch
-- 
2.47.3



_______________________________________________
pve-devel mailing list
pve-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel