block: fix detect-zeroes= with BDRV_REQ_REGISTERED_BUF

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.ebner@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.ebner@proxmox.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230207203719.242926-2-stefanha@redhat.com>
(cherry picked from commit 3c5867156eb81c7c71611d078b2c5c2c863f884a)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/block/io.c b/block/io.c
index b9424024f9b093ad3a5a67ddb9c22fdd8a46b4b9..bbaa0d1b2d4833018b2f9225f15f28cc6f0b88da 100644 (file)
--- a/block/io.c
+++ b/block/io.c
@@ -2087,6 +2087,9 @@ 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) {