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block: use pwrite_zeroes_alignment when writing first sector

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Since commit 5634622bcb ("file-posix: allow BLKZEROOUT with -t
writeback"), qemu-img create errors out on a Linux loop block device
with a 4 KB sector size:

  # dd if=/dev/zero of=blockfile bs=1M count=1024
  # losetup --sector-size 4096 /dev/loop0 blockfile
  # qemu-img create -f raw /dev/loop0 1G
  Formatting '/dev/loop0', fmt=raw size=1073741824
  qemu-img: /dev/loop0: Failed to clear the new image's first sector: Invalid argument

Use the pwrite_zeroes_alignment block limit to avoid misaligned
fallocate(2) or ioctl(BLKZEROOUT) in the block/file-posix.c block
driver.

Cc: qemu-stable@nongnu.org
Fixes: 5634622bcb ("file-posix: allow BLKZEROOUT with -t writeback")
Reported-by: Jean-Louis Dupond <jean-louis@dupond.be>
Buglink: https://gitlab.com/qemu-project/qemu/-/issues/3127
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20251007141700.71891-3-stefanha@redhat.com>
Tested-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2025-10-07 10:16:59 -04:00 • committed by Kevin Wolf
parent 98e788b91a
commit d704a13d2c
3 changed files with 14 additions and 1 deletions
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3
block.c
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@ -606,12 +606,13 @@ create_file_fallback_zero_first_sector(BlockBackend *blk,
int64_t current_size,
Error **errp)
{
uint32_t alignment = blk_get_pwrite_zeroes_alignment(blk);
int64_t bytes_to_clear;
int ret;
GLOBAL_STATE_CODE();
bytes_to_clear = MIN(current_size, BDRV_SECTOR_SIZE);
bytes_to_clear = MIN(current_size, MAX(BDRV_SECTOR_SIZE, alignment));
if (bytes_to_clear) {
ret = blk_co_pwrite_zeroes(blk, 0, bytes_to_clear, BDRV_REQ_MAY_UNMAP);
if (ret < 0) {