mount-util: avoid unnecessary mount_setattr() call in make_fsmount()

If .attr_set is zero (and .att_clr, .propagation too), then there's no
point in calling mount_setattr().

Fixes: #37062
Note that this optimization is not precisely load-bearing anymore, since
3cc23a2c2345eb188551565349c89ec1fa8f650f got merged which removes the
only caller of make_fsmount() that might trigger it. But it's worth
fixing generic code anyway, in case it gets used like this later again.

diff --git a/src/shared/mount-util.c b/src/shared/mount-util.c
index 9a1cc31fac6c66a04680bf6667d2e4a70bd08fb2..8679db705734a5ddeff442299534b921f9b58729 100644 (file)
--- a/src/shared/mount-util.c
+++ b/src/shared/mount-util.c
@@ -1854,11 +1854,11 @@ int make_fsmount(
         if (mnt_fd < 0)
                 return log_full_errno(error_log_level, errno, "Failed to create mount fd for \"%s\" (\"%s\"): %m", what, type);
 
-        if (mount_setattr(mnt_fd, "", AT_EMPTY_PATH|AT_RECURSIVE,
-                          &(struct mount_attr) {
-                                  .attr_set = ms_flags_to_mount_attr(f) | (userns_fd >= 0 ? MOUNT_ATTR_IDMAP : 0),
-                                  .userns_fd = userns_fd,
-                          }, MOUNT_ATTR_SIZE_VER0) < 0)
+        struct mount_attr ma = {
+                .attr_set = ms_flags_to_mount_attr(f) | (userns_fd >= 0 ? MOUNT_ATTR_IDMAP : 0),
+                .userns_fd = userns_fd,
+        };
+        if (ma.attr_set != 0 && mount_setattr(mnt_fd, "", AT_EMPTY_PATH|AT_RECURSIVE, &ma, MOUNT_ATTR_SIZE_VER0) < 0)
                 return log_full_errno(error_log_level,
                                       errno,
                                       "Failed to set mount flags for \"%s\" (\"%s\"): %m",