UBIFS: respect MS_SILENT mount flag

When attempting to mount a non-ubifs formatted volume, lots of error
messages (including a stack dump) are thrown to the kernel log even if
the MS_SILENT mount flag is set.
Fix this by introducing adding an additional state-variable in
struct ubifs_info and suppress error messages in ubifs_read_node if
MS_SILENT is set.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

fs/ubifs/super.c

@@ -1149,6 +1149,9 @@ static int mount_ubifs(struct ubifs_info *c)
 	size_t sz;
 
 	c->ro_mount = !!(c->vfs_sb->s_flags & MS_RDONLY);
+	/* Suppress error messages while probing if MS_SILENT is set */
+	c->probing = !!(c->vfs_sb->s_flags & MS_SILENT);
+
 	err = init_constants_early(c);
 	if (err)
 		return err;
@@ -1214,6 +1217,8 @@ static int mount_ubifs(struct ubifs_info *c)
 	if (err)
 		goto out_free;
 
+	c->probing = 0;
+
 	/*
 	 * Make sure the compressor which is set as default in the superblock
 	 * or overridden by mount options is actually compiled in.