block: respect error code from bdrv_getlength in handle_aiocb_write_zeroes

Original idea beyond the code in question was the following: we have failed
to write zeroes with fallocate(FALLOC_FL_ZERO_RANGE) as the simplest
approach and via fallocate(FALLOC_FL_PUNCH_HOLE)/fallocate(0). We have the
only chance now: if the request comes beyond end of the file. Thus we
should calculate file length and respect the error code from that op.
Signed-off-by: NDenis V. Lunev <den@openvz.org>
CC: Markus Armbruster <armbru@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

block/file-posix.c

@@ -1339,6 +1339,9 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb)
 #if defined(CONFIG_FALLOCATE) || defined(CONFIG_XFS)
     BDRVRawState *s = aiocb->bs->opaque;
 #endif
+#ifdef CONFIG_FALLOCATE
+    int64_t len;
+#endif
 
     if (aiocb->aio_type & QEMU_AIO_BLKDEV) {
         return handle_aiocb_write_zeroes_block(aiocb);
@@ -1381,7 +1384,10 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb)
 #endif
 
 #ifdef CONFIG_FALLOCATE
-    if (s->has_fallocate && aiocb->aio_offset >= bdrv_getlength(aiocb->bs)) {
+    /* Last resort: we are trying to extend the file with zeroed data. This
+     * can be done via fallocate(fd, 0) */
+    len = bdrv_getlength(aiocb->bs);
+    if (s->has_fallocate && len >= 0 && aiocb->aio_offset >= len) {
         int ret = do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes);
         if (ret == 0 || ret != -ENOTSUP) {
             return ret;