OpenZFS 7277 - zdb should be able to print zfs_dbgmsg's

Porting notes:
- 'zfs_dbgmsg_print()' reintroduced to userspace.

Authored by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Igor Kozhukhov <ikozhukhov@gmail.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/7277
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/29bdd2f
Closes #5684

cmd/zdb/zdb.c

@@ -21,7 +21,7 @@
 
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2016 by Delphix. All rights reserved.
  * Copyright (c) 2015, Intel Corporation.
  */
 
@@ -126,7 +126,7 @@ static void
 usage(void)
 {
 	(void) fprintf(stderr,
-	    "Usage: %s [-CumMdibcsDvhLXFPA] [-t txg] [-e [-p path...]] "
+	    "Usage: %s [-CumMdibcsDvhLXFPAG] [-t txg] [-e [-p path...]] "
 	    "[-U config] [-I inflight I/Os] [-x dumpdir] poolname [object...]\n"
 	    "       %s [-divPA] [-e -p path...] [-U config] dataset "
 	    "[object...]\n"
@@ -187,12 +187,23 @@ usage(void)
 	(void) fprintf(stderr, "        -I <number of inflight I/Os> -- "
 	    "specify the maximum number of "
 	    "checksumming I/Os [default is 200]\n");
+	(void) fprintf(stderr, "        -G dump zfs_dbgmsg buffer before "
+	    "exiting\n");
 	(void) fprintf(stderr, "Specify an option more than once (e.g. -bb) "
 	    "to make only that option verbose\n");
 	(void) fprintf(stderr, "Default is to dump everything non-verbosely\n");
 	exit(1);
 }
 
+static void
+dump_debug_buffer(void)
+{
+	if (dump_opt['G']) {
+		(void) printf("\n");
+		zfs_dbgmsg_print("zdb");
+	}
+}
+
 /*
  * Called for usage errors that are discovered after a call to spa_open(),
  * dmu_bonus_hold(), or pool_match().  abort() is called for other errors.
@@ -209,6 +220,8 @@ fatal(const char *fmt, ...)
 	va_end(ap);
 	(void) fprintf(stderr, "\n");
 
+	dump_debug_buffer();
+
 	exit(1);
 }
 
@@ -3197,9 +3210,11 @@ dump_zpool(spa_t *spa)
 	if (dump_opt['h'])
 		dump_history(spa);
 
-	if (rc != 0)
+	if (rc != 0) {
+		dump_debug_buffer();
 		exit(rc);
 	}
+}
 
 #define	ZDB_FLAG_CHECKSUM	0x0001
 #define	ZDB_FLAG_DECOMPRESS	0x0002
@@ -3692,7 +3707,7 @@ main(int argc, char **argv)
 		spa_config_path = spa_config_path_env;
 
 	while ((c = getopt(argc, argv,
-	    "bcdhilmMI:suCDRSAFLXx:evp:t:U:PV")) != -1) {
+	    "bcdhilmMI:suCDRSAFLXx:evp:t:U:PVG")) != -1) {
 		switch (c) {
 		case 'b':
 		case 'c':
@@ -3708,6 +3723,7 @@ main(int argc, char **argv)
 		case 'M':
 		case 'R':
 		case 'S':
+		case 'G':
 			dump_opt[c]++;
 			dump_all = 0;
 			break;
@@ -3939,6 +3955,8 @@ main(int argc, char **argv)
 	fuid_table_destroy();
 	sa_loaded = B_FALSE;
 
+	dump_debug_buffer();
+
 	libzfs_fini(g_zfs);
 	kernel_fini();
 

include/sys/zfs_debug.h

@@ -73,6 +73,7 @@ extern void zfs_dbgmsg_fini(void);
 
 #ifndef _KERNEL
 extern int dprintf_find_string(const char *string);
+extern void zfs_dbgmsg_print(const char *tag);
 #endif
 
 #ifdef	__cplusplus

man/man8/zdb.8

@@ -11,15 +11,15 @@
 .\"
 .\"
 .\" Copyright 2012, Richard Lowe.
-.\" Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+.\" Copyright (c) 2012, 2016 by Delphix. All rights reserved.
 .\"
-.TH "ZDB" "8" "February 15, 2012" "" ""
+.TH "ZDB" "8" "Feb 4, 2016" "" ""
 
 .SH "NAME"
 \fBzdb\fR - Display zpool debugging and consistency information
 
 .SH "SYNOPSIS"
-\fBzdb\fR [-CumdibcsDvhLMXFPA] [-e [-p \fIpath\fR...]] [-t \fItxg\fR]
+\fBzdb\fR [-CumdibcsDvhLMXFPAG] [-e [-p \fIpath\fR...]] [-t \fItxg\fR]
     [-U \fIcache\fR] [-I \fIinflight I/Os\fR] [-x \fIdumpdir\fR]
     [\fIpoolname\fR [\fIobject\fR ...]]
 
@@ -397,6 +397,17 @@ Attempt to make an unreadable pool readable by trying progressively older
 transactions.
 .RE
 
+.sp
+.ne 2
+.na
+\fB-G\fR
+.ad
+.sp .6
+.RS 4n
+Dump the contents of the zfs_dbgmsg buffer before exiting zdb. zfs_dbgmsg is
+a buffer used by ZFS to dump advanced debug information.
+.RE
+
 .sp
 .ne 2
 .na

module/zfs/zfs_debug.c

@@ -228,6 +228,21 @@ __dprintf(const char *file, const char *func, int line, const char *fmt, ...)
 
 	kmem_free(buf, size);
 }
+
+#else
+
+void
+zfs_dbgmsg_print(const char *tag)
+{
+	zfs_dbgmsg_t *zdm;
+
+	(void) printf("ZFS_DBGMSG(%s):\n", tag);
+	mutex_enter(&zfs_dbgmsgs_lock);
+	for (zdm = list_head(&zfs_dbgmsgs); zdm;
+	    zdm = list_next(&zfs_dbgmsgs, zdm))
+		(void) printf("%s\n", zdm->zdm_msg);
+	mutex_exit(&zfs_dbgmsgs_lock);
+}
 #endif /* _KERNEL */
 
 #ifdef _KERNEL