When a write request is converted into a write zeroes request by the detect-zeroes= feature, it is no longer associated with an I/O buffer. The BDRV_REQ_REGISTERED_BUF flag doesn't make sense without an I/O buffer and must be cleared because bdrv_co_do_pwrite_zeroes() fails with -EINVAL when it's set.
Fiona Ebner <f.eb...@proxmox.com> bisected and diagnosed this QEMU 7.2 regression where writes containing zeroes to a blockdev with discard=unmap,detect-zeroes=unmap fail. Buglink: https://gitlab.com/qemu-project/qemu/-/issues/1404 Fixes: e8b6535533be ("block: add BDRV_REQ_REGISTERED_BUF request flag") Tested-by: Fiona Ebner <f.eb...@proxmox.com> Cc: qemu-sta...@nongnu.org Reviewed-by: Eric Blake <ebl...@redhat.com> Reviewed-by: Hanna Czenczek <hre...@redhat.com> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> --- block/io.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/io.c b/block/io.c index 2dc0c13e41..d2be37b11e 100644 --- a/block/io.c +++ b/block/io.c @@ -1926,6 +1926,9 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child, if (bs->detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP) { flags |= BDRV_REQ_MAY_UNMAP; } + + /* Can't use optimization hint with bufferless zero write */ + flags &= ~BDRV_REQ_REGISTERED_BUF; } if (ret < 0) { -- 2.39.1
