file-posix: Support BDRV_REQ_ZERO_WRITE for truncate

For regular files, we always get BDRV_REQ_ZERO_WRITE behaviour from the
OS, so we can advertise the flag and just ignore it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200424125448.63318-7-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/file-posix.c b/block/file-posix.c
index 58326a0..bf09ad8 100644 (file)
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -702,6 +702,10 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
 #endif
 
     bs->supported_zero_flags = BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK;
+    if (S_ISREG(st.st_mode)) {
+        /* When extending regular files, we get zeros from the OS */
+        bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;
+    }
     ret = 0;
 fail:
     if (filename && (bdrv_flags & BDRV_O_TEMPORARY)) {