scoutfs: add scoutfs_corruption()

Add a helper for printing a message warning about corruption.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/format.h

@@ -645,4 +645,13 @@ struct scoutfs_fid {
 #define FILEID_SCOUTFS			0x81
 #define FILEID_SCOUTFS_WITH_PARENT	0x82
 
+/*
+ * Identifiers for sources of corruption that can generate messages.
+ */
+enum {
+	SC_NR_SOURCES,
+};
+
+#define SC_NR_LONGS DIV_ROUND_UP(SC_NR_SOURCES, BITS_PER_LONG)
+
 #endif

kmod/src/msg.h

@@ -1,6 +1,7 @@
 #ifndef _SCOUTFS_MSG_H_
 #define _SCOUTFS_MSG_H_
 
+#include <linux/bitops.h>
 #include "key.h"
 
 void __printf(4, 5) scoutfs_msg(struct super_block *sb, const char *prefix,
@@ -23,4 +24,25 @@ do {									\
 	}								\
 } while (0)								\
 
+/*
+ * Each message is only generated once per volume.  Remounting resets
+ * the messages.
+ */
+#define scoutfs_corruption(sb, which, counter, fmt, args...)		\
+do {									\
+	__typeof__(sb) _sb = (sb);					\
+	struct scoutfs_sb_info *_sbi = SCOUTFS_SB(_sb);			\
+	unsigned int _bit = (which);					\
+									\
+	if (WARN_ON_ONCE(_bit >= SC_NR_SOURCES))			\
+		break;							\
+									\
+	scoutfs_inc_counter(_sb, counter);				\
+	if (!test_and_set_bit(_bit, _sbi->corruption_messages_once)) {	\
+		scoutfs_err(_sb, "corruption (see scoutfs-corruption(5)): " \
+			    #which ": " fmt, ##args);			\
+		dump_stack();						\
+	}								\
+} while (0)								\
+
 #endif

kmod/src/super.h

@@ -70,6 +70,8 @@ struct scoutfs_sb_info {
 	struct dentry *debug_root;
 
 	bool shutdown;
+
+	unsigned long corruption_messages_once[SC_NR_LONGS];
 };
 
 static inline struct scoutfs_sb_info *SCOUTFS_SB(struct super_block *sb)