block/file-posix: Try other fallbacks after invalid FALLOC_FL_ZERO_RANGE

If fallocate(... FALLOC_FL_ZERO_RANGE ...) returns EINVAL, it's likely
an indication that the file system is buggy and does not implement
unaligned accesses right. We still might be lucky with the other
fallback fallocate() calls later in this function, though, so we should
not return immediately and try the others first.
Since FALLOC_FL_ZERO_RANGE could also return EINVAL if the file descriptor
is not a regular file, we ignore this filesystem bug silently, without
printing an error message for the user.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210527172020.847617-3-thuth@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/file-posix.c

@@ -1625,17 +1625,17 @@ static int handle_aiocb_write_zeroes(void *opaque)
     if (s->has_write_zeroes) {
         int ret = do_fallocate(s->fd, FALLOC_FL_ZERO_RANGE,
                                aiocb->aio_offset, aiocb->aio_nbytes);
-        if (ret == -EINVAL) {
-            /*
-             * Allow falling back to pwrite for file systems that
-             * do not support fallocate() for an unaligned byte range.
-             */
-            return -ENOTSUP;
-        }
-        if (ret == 0 || ret != -ENOTSUP) {
+        if (ret == -ENOTSUP) {
+            s->has_write_zeroes = false;
+        } else if (ret == 0 || ret != -EINVAL) {
             return ret;
         }
-        s->has_write_zeroes = false;
+        /*
+         * Note: Some file systems do not like unaligned byte ranges, and
+         * return EINVAL in such a case, though they should not do it according
+         * to the man-page of fallocate(). Thus we simply ignore this return
+         * value and try the other fallbacks instead.
+         */
     }
 #endif