Add dbgmsg kstat

Internally ZFS keeps a small log to facilitate debugging.  By default
the log is disabled, to enable it set zfs_dbgmsg_enable=1.  The contents
of the log can be accessed by reading the /proc/spl/kstat/zfs/dbgmsg file.
Writing 0 to this proc file clears the log.

$ echo 1 >/sys/module/zfs/parameters/zfs_dbgmsg_enable
$ echo 0 >/proc/spl/kstat/zfs/dbgmsg
$ zpool import tank
$ cat /proc/spl/kstat/zfs/dbgmsg
1 0 0x01 -1 0 2492357525542 2525836565501
timestamp    message
1441141408   spa=tank async request task=1
1441141408   txg 70 open pool version 5000; software version 5000/5; ...
1441141409   spa=tank async request task=32
1441141409   txg 72 import pool version 5000; software version 5000/5; ...
1441141414   command: lt-zpool import tank

Note the zfs_dbgmsg() and dprintf() functions are both now mapped to
the same log.  As mentioned above the kernel debug log can be accessed
though the /proc/spl/kstat/zfs/dbgmsg kstat.  For user space consumers
log messages are immediately written to stdout after applying the
ZFS_DEBUG environment variable.

$ ZFS_DEBUG=on ./cmd/ztest/ztest -V

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ned Bass <[email protected]>
Closes #3728

2 files changed, 4 insertions, 34 deletions

diff --git a/include/sys/trace_dbgmsg.h b/include/sys/trace_dbgmsg.h
index 24b34bcf3..e493a4580 100644
--- a/include/sys/trace_dbgmsg.h
+++ b/include/sys/trace_dbgmsg.h
@@ -37,32 +37,6 @@
  */
 
 /*
- * Generic support for one argument tracepoints of the form:
- *
- * DTRACE_PROBE1(...,
- *     const char *, ...);
- */
-
-DECLARE_EVENT_CLASS(zfs_dbgmsg_class,
-	TP_PROTO(const char *msg),
-	TP_ARGS(msg),
-	TP_STRUCT__entry(
-	    __string(msg, msg)
-	),
-	TP_fast_assign(
-	    __assign_str(msg, msg);
-	),
-	TP_printk("%s", __get_str(msg))
-);
-
-#define	DEFINE_DBGMSG_EVENT(name) \
-DEFINE_EVENT(zfs_dbgmsg_class, name, \
-	TP_PROTO(const char *msg), \
-	TP_ARGS(msg))
-DEFINE_DBGMSG_EVENT(zfs_zfs__dbgmsg);
-
-
-/*
  * Generic support for four argument tracepoints of the form:
  *
  * DTRACE_PROBE4(...,
diff --git a/include/sys/zfs_debug.h b/include/sys/zfs_debug.h
index 1a7062408..2f0064ee0 100644
--- a/include/sys/zfs_debug.h
+++ b/include/sys/zfs_debug.h
@@ -51,28 +51,24 @@ extern int zfs_free_leak_on_eio;
 #define	ZFS_DEBUG_ZIO_FREE		(1<<6)
 #define	ZFS_DEBUG_HISTOGRAM_VERIFY	(1<<7)
 
-#if defined(HAVE_DECLARE_EVENT_CLASS) || !defined(_KERNEL)
 extern void __dprintf(const char *file, const char *func,
     int line, const char *fmt, ...);
 #define	dprintf(...) \
-	if (zfs_flags & ZFS_DEBUG_DPRINTF) \
-		__dprintf(__FILE__, __func__, __LINE__, __VA_ARGS__)
-#else
-#define	dprintf(...) ((void)0)
-#endif /* HAVE_DECLARE_EVENT_CLASS || !_KERNEL */
+	__dprintf(__FILE__, __func__, __LINE__, __VA_ARGS__)
+#define	zfs_dbgmsg(...) \
+	__dprintf(__FILE__, __func__, __LINE__, __VA_ARGS__)
 
 extern void zfs_panic_recover(const char *fmt, ...);
 
 typedef struct zfs_dbgmsg {
 	list_node_t zdm_node;
 	time_t zdm_timestamp;
+	int zdm_size;
 	char zdm_msg[1]; /* variable length allocation */
 } zfs_dbgmsg_t;
 
 extern void zfs_dbgmsg_init(void);
 extern void zfs_dbgmsg_fini(void);
-extern void zfs_dbgmsg(const char *fmt, ...);
-extern void zfs_dbgmsg_print(const char *tag);
 
 #ifndef _KERNEL
 extern int dprintf_find_string(const char *string);