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/ubifs.h

@@ -51,6 +51,15 @@
 #define ubifs_warn(fmt, ...)                                        \
 	pr_warn("UBIFS warning (pid %d): %s: " fmt "\n",            \
 		current->pid, __func__, ##__VA_ARGS__)
+/*
+ * A variant of 'ubifs_err()' which takes the UBIFS file-sytem description
+ * object as an argument.
+ */
+#define ubifs_errc(c, fmt, ...)                                     \
+	do {                                                        \
+		if (!(c)->probing)                                  \
+			ubifs_err(fmt, ##__VA_ARGS__);              \
+	} while (0)
 
 /* UBIFS file system VFS magic number */
 #define UBIFS_SUPER_MAGIC 0x24051905
@@ -1209,6 +1218,7 @@ struct ubifs_debug_info;
  * @need_recovery: %1 if the file-system needs recovery
  * @replaying: %1 during journal replay
  * @mounting: %1 while mounting
+ * @probing: %1 while attempting to mount if MS_SILENT mount flag is set
  * @remounting_rw: %1 while re-mounting from R/O mode to R/W mode
  * @replay_list: temporary list used during journal replay
  * @replay_buds: list of buds to replay
@@ -1441,6 +1451,7 @@ struct ubifs_info {
 	unsigned int replaying:1;
 	unsigned int mounting:1;
 	unsigned int remounting_rw:1;
+	unsigned int probing:1;
 	struct list_head replay_list;
 	struct list_head replay_buds;
 	unsigned long long cs_sqnum;