Swap DTRACE_PROBE* with Linux tracepoints

This patch leverages Linux tracepoints from within the ZFS on Linux
code base. It also refactors the debug code to bring it back in sync
with Illumos.

The information exported via tracepoints can be used for a variety of
reasons (e.g. debugging, tuning, general exploration/understanding,
etc). It is advantageous to use Linux tracepoints as the mechanism to
export this kind of information (as opposed to something else) for a
number of reasons:

    * A number of external tools can make use of our tracepoints
      "automatically" (e.g. perf, systemtap)
    * Tracepoints are designed to be extremely cheap when disabled
    * It's one of the "accepted" ways to export this kind of
      information; many other kernel subsystems use tracepoints too.

Unfortunately, though, there are a few caveats as well:

    * Linux tracepoints appear to only be available to GPL licensed
      modules due to the way certain kernel functions are exported.
      Thus, to actually make use of the tracepoints introduced by this
      patch, one might have to patch and re-compile the kernel;
      exporting the necessary functions to non-GPL modules.

    * Prior to upstream kernel version v3.14-rc6-30-g66cc69e, Linux
      tracepoints are not available for unsigned kernel modules
      (tracepoints will get disabled due to the module's 'F' taint).
      Thus, one either has to sign the zfs kernel module prior to
      loading it, or use a kernel versioned v3.14-rc6-30-g66cc69e or
      newer.

Assuming the above two requirements are satisfied, lets look at an
example of how this patch can be used and what information it exposes
(all commands run as 'root'):

    # list all zfs tracepoints available

    $ ls /sys/kernel/debug/tracing/events/zfs
    enable              filter              zfs_arc__delete
    zfs_arc__evict      zfs_arc__hit        zfs_arc__miss
    zfs_l2arc__evict    zfs_l2arc__hit      zfs_l2arc__iodone
    zfs_l2arc__miss     zfs_l2arc__read     zfs_l2arc__write
    zfs_new_state__mfu  zfs_new_state__mru

    # enable all zfs tracepoints, clear the tracepoint ring buffer

    $ echo 1 > /sys/kernel/debug/tracing/events/zfs/enable
    $ echo 0 > /sys/kernel/debug/tracing/trace

    # import zpool called 'tank', inspect tracepoint data (each line was
    # truncated, they're too long for a commit message otherwise)

    $ zpool import tank
    $ cat /sys/kernel/debug/tracing/trace | head -n35
    # tracer: nop
    #
    # entries-in-buffer/entries-written: 1219/1219   #P:8
    #
    #                              _-----=> irqs-off
    #                             / _----=> need-resched
    #                            | / _---=> hardirq/softirq
    #                            || / _--=> preempt-depth
    #                            ||| /     delay
    #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
    #              | |       |   ||||       |         |
            lt-zpool-30132 [003] .... 91344.200050: zfs_arc__miss: hdr...
          z_rd_int/0-30156 [003] .... 91344.200611: zfs_new_state__mru...
            lt-zpool-30132 [003] .... 91344.201173: zfs_arc__miss: hdr...
          z_rd_int/1-30157 [003] .... 91344.201756: zfs_new_state__mru...
            lt-zpool-30132 [003] .... 91344.201795: zfs_arc__miss: hdr...
          z_rd_int/2-30158 [003] .... 91344.202099: zfs_new_state__mru...
            lt-zpool-30132 [003] .... 91344.202126: zfs_arc__hit: hdr ...
            lt-zpool-30132 [003] .... 91344.202130: zfs_arc__hit: hdr ...
            lt-zpool-30132 [003] .... 91344.202134: zfs_arc__hit: hdr ...
            lt-zpool-30132 [003] .... 91344.202146: zfs_arc__miss: hdr...
          z_rd_int/3-30159 [003] .... 91344.202457: zfs_new_state__mru...
            lt-zpool-30132 [003] .... 91344.202484: zfs_arc__miss: hdr...
          z_rd_int/4-30160 [003] .... 91344.202866: zfs_new_state__mru...
            lt-zpool-30132 [003] .... 91344.202891: zfs_arc__hit: hdr ...
            lt-zpool-30132 [001] .... 91344.203034: zfs_arc__miss: hdr...
          z_rd_iss/1-30149 [001] .... 91344.203749: zfs_new_state__mru...
            lt-zpool-30132 [001] .... 91344.203789: zfs_arc__hit: hdr ...
            lt-zpool-30132 [001] .... 91344.203878: zfs_arc__miss: hdr...
          z_rd_iss/3-30151 [001] .... 91344.204315: zfs_new_state__mru...
            lt-zpool-30132 [001] .... 91344.204332: zfs_arc__hit: hdr ...
            lt-zpool-30132 [001] .... 91344.204337: zfs_arc__hit: hdr ...
            lt-zpool-30132 [001] .... 91344.204352: zfs_arc__hit: hdr ...
            lt-zpool-30132 [001] .... 91344.204356: zfs_arc__hit: hdr ...
            lt-zpool-30132 [001] .... 91344.204360: zfs_arc__hit: hdr ...

To highlight the kind of detailed information that is being exported
using this infrastructure, I've taken the first tracepoint line from the
output above and reformatted it such that it fits in 80 columns:

    lt-zpool-30132 [003] .... 91344.200050: zfs_arc__miss:
        hdr {
            dva 0x1:0x40082
            birth 15491
            cksum0 0x163edbff3a
            flags 0x640
            datacnt 1
            type 1
            size 2048
            spa 3133524293419867460
            state_type 0
            access 0
            mru_hits 0
            mru_ghost_hits 0
            mfu_hits 0
            mfu_ghost_hits 0
            l2_hits 0
            refcount 1
        } bp {
            dva0 0x1:0x40082
            dva1 0x1:0x3000e5
            dva2 0x1:0x5a006e
            cksum 0x163edbff3a:0x75af30b3dd6:0x1499263ff5f2b:0x288bd118815e00
            lsize 2048
        } zb {
            objset 0
            object 0
            level -1
            blkid 0
        }

For the specific tracepoint shown here, 'zfs_arc__miss', data is
exported detailing the arc_buf_hdr_t (hdr), blkptr_t (bp), and
zbookmark_t (zb) that caused the ARC miss (down to the exact DVA!).
This kind of precise and detailed information can be extremely valuable
when trying to answer certain kinds of questions.

For anybody unfamiliar but looking to build on this, I found the XFS
source code along with the following three web links to be extremely
helpful:

    * http://lwn.net/Articles/379903/
    * http://lwn.net/Articles/381064/
    * http://lwn.net/Articles/383362/

I should also node the more "boring" aspects of this patch:

    * The ZFS_LINUX_COMPILE_IFELSE autoconf macro was modified to
       support a sixth paramter. This parameter is used to populate the
       contents of the new conftest.h file. If no sixth parameter is
       provided, conftest.h will be empty.

    * The ZFS_LINUX_TRY_COMPILE_HEADER autoconf macro was introduced.
      This macro is nearly identical to the ZFS_LINUX_TRY_COMPILE macro,
      except it has support for a fifth option that is then passed as
      the sixth parameter to ZFS_LINUX_COMPILE_IFELSE.

These autoconf changes were needed to test the availability of the Linux
tracepoint macros. Due to the odd nature of the Linux tracepoint macro
API, a separate ".h" must be created (the path and filename is used
internally by the kernel's define_trace.h file).

    * The HAVE_DECLARE_EVENT_CLASS autoconf macro was introduced. This
      is to determine if we can safely enable the Linux tracepoint
      functionality. We need to selectively disable the tracepoint code
      due to the kernel exporting certain functions as GPL only. Without
      this check, the build process will fail at link time.

In addition, the SET_ERROR macro was modified into a tracepoint as well.
To do this, the 'sdt.h' file was moved into the 'include/sys' directory
and now contains a userspace portion and a kernel space portion. The
dprintf and zfs_dbgmsg* interfaces are now implemented as tracepoint as
well.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

config/kernel-declare-event-class.m4

@@ -0,0 +1,59 @@
+dnl #
+dnl # Ensure the DECLARE_EVENT_CLASS macro is available to non-GPL modules.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_DECLARE_EVENT_CLASS], [
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-I\$(src)"
+
+	AC_MSG_CHECKING([whether DECLARE_EVENT_CLASS() is available])
+	ZFS_LINUX_TRY_COMPILE_HEADER([
+		#include <linux/module.h>
+		MODULE_LICENSE(ZFS_META_LICENSE);
+
+		#define CREATE_TRACE_POINTS
+		#include "conftest.h"
+	],[
+		trace_zfs_autoconf_event_one(1UL);
+		trace_zfs_autoconf_event_two(2UL);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_DECLARE_EVENT_CLASS, 1,
+		          [DECLARE_EVENT_CLASS() is available])
+	],[
+		AC_MSG_RESULT(no)
+	],[
+		#if !defined(_CONFTEST_H) || defined(TRACE_HEADER_MULTI_READ)
+		#define _CONFTEST_H
+
+		#undef  TRACE_SYSTEM
+		#define TRACE_SYSTEM zfs
+		#include <linux/tracepoint.h>
+
+		DECLARE_EVENT_CLASS(zfs_autoconf_event_class,
+			TP_PROTO(unsigned long i),
+			TP_ARGS(i),
+			TP_STRUCT__entry(
+				__field(unsigned long, i)
+			),
+			TP_fast_assign(
+				__entry->i = i;
+			),
+			TP_printk("i = %lu", __entry->i)
+		);
+
+		#define DEFINE_AUTOCONF_EVENT(name) \
+		DEFINE_EVENT(zfs_autoconf_event_class, name, \
+			TP_PROTO(unsigned long i), \
+			TP_ARGS(i))
+		DEFINE_AUTOCONF_EVENT(zfs_autoconf_event_one);
+		DEFINE_AUTOCONF_EVENT(zfs_autoconf_event_two);
+
+		#endif /* _CONFTEST_H */
+
+		#undef  TRACE_INCLUDE_PATH
+		#define TRACE_INCLUDE_PATH .
+		#define TRACE_INCLUDE_FILE conftest
+		#include <trace/define_trace.h>
+	])
+	EXTRA_KCFLAGS="$tmp_flags"
+])

config/kernel.m4

@@ -6,6 +6,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_SPL
 	ZFS_AC_TEST_MODULE
 	ZFS_AC_KERNEL_CONFIG
+	ZFS_AC_KERNEL_DECLARE_EVENT_CLASS
 	ZFS_AC_KERNEL_BDEV_BLOCK_DEVICE_OPERATIONS
 	ZFS_AC_KERNEL_BLOCK_DEVICE_OPERATIONS_RELEASE_VOID
 	ZFS_AC_KERNEL_TYPE_FMODE_T
@@ -506,9 +507,18 @@ AC_DEFUN([ZFS_AC_KERNEL_CONFIG_DEBUG_LOCK_ALLOC], [
 ])
 
 dnl #
-dnl # ZFS_LINUX_CONFTEST
+dnl # ZFS_LINUX_CONFTEST_H
 dnl #
-AC_DEFUN([ZFS_LINUX_CONFTEST], [
+AC_DEFUN([ZFS_LINUX_CONFTEST_H], [
+cat - <<_ACEOF >conftest.h
+$1
+_ACEOF
+])
+
+dnl #
+dnl # ZFS_LINUX_CONFTEST_C
+dnl #
+AC_DEFUN([ZFS_LINUX_CONFTEST_C], [
 cat confdefs.h - <<_ACEOF >conftest.c
 $1
 _ACEOF
@@ -534,13 +544,14 @@ dnl #
 dnl # ZFS_LINUX_COMPILE_IFELSE / like AC_COMPILE_IFELSE
 dnl #
 AC_DEFUN([ZFS_LINUX_COMPILE_IFELSE], [
-	m4_ifvaln([$1], [ZFS_LINUX_CONFTEST([$1])])
+	m4_ifvaln([$1], [ZFS_LINUX_CONFTEST_C([$1])])
+	m4_ifvaln([$6], [ZFS_LINUX_CONFTEST_H([$6])], [ZFS_LINUX_CONFTEST_H([])])
 	rm -Rf build && mkdir -p build && touch build/conftest.mod.c
 	echo "obj-m := conftest.o" >build/Makefile
 	modpost_flag=''
 	test "x$enable_linux_builtin" = xyes && modpost_flag='modpost=true' # fake modpost stage
 	AS_IF(
-		[AC_TRY_COMMAND(cp conftest.c build && make [$2] -C $LINUX_OBJ EXTRA_CFLAGS="-Werror $EXTRA_KCFLAGS" $ARCH_UM M=$PWD/build $modpost_flag) >/dev/null && AC_TRY_COMMAND([$3])],
+		[AC_TRY_COMMAND(cp conftest.c conftest.h build && make [$2] -C $LINUX_OBJ EXTRA_CFLAGS="-Werror $EXTRA_KCFLAGS" $ARCH_UM M=$PWD/build $modpost_flag) >/dev/null && AC_TRY_COMMAND([$3])],
 		[$4],
 		[_AC_MSG_LOG_CONFTEST m4_ifvaln([$5],[$5])]
 	)
@@ -627,3 +638,16 @@ AC_DEFUN([ZFS_LINUX_TRY_COMPILE_SYMBOL], [
 		fi
 	fi
 ])
+
+dnl #
+dnl # ZFS_LINUX_TRY_COMPILE_HEADER
+dnl # like ZFS_LINUX_TRY_COMPILE, except the contents conftest.h are
+dnl # provided via the fifth parameter
+dnl #
+AC_DEFUN([ZFS_LINUX_TRY_COMPILE_HEADER],
+	[ZFS_LINUX_COMPILE_IFELSE(
+	[AC_LANG_SOURCE([ZFS_LANG_PROGRAM([[$1]], [[$2]])])],
+	[modules],
+	[test -s build/conftest.o],
+	[$3], [$4], [AC_LANG_SOURCE([$5])])
+])

include/sys/Makefile.am

@@ -40,11 +40,13 @@ COMMON_H = \
 	$(top_srcdir)/include/sys/rrwlock.h \
 	$(top_srcdir)/include/sys/sa.h \
 	$(top_srcdir)/include/sys/sa_impl.h \
+	$(top_srcdir)/include/sys/sdt.h \
 	$(top_srcdir)/include/sys/spa_boot.h \
 	$(top_srcdir)/include/sys/space_map.h \
 	$(top_srcdir)/include/sys/space_reftree.h \
 	$(top_srcdir)/include/sys/spa.h \
 	$(top_srcdir)/include/sys/spa_impl.h \
+	$(top_srcdir)/include/sys/trace.h \
 	$(top_srcdir)/include/sys/txg.h \
 	$(top_srcdir)/include/sys/txg_impl.h \
 	$(top_srcdir)/include/sys/u8_textprep_data.h \

include/sys/sdt.h

@@ -0,0 +1,70 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License, Version 1.0 only
+ * (the "License").  You may not use this file except in compliance
+ * with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
+ * Use is subject to license terms.
+ */
+
+#ifndef _SYS_SDT_H
+#define	_SYS_SDT_H
+
+#ifndef _KERNEL
+
+#define	ZFS_PROBE(a)			((void) 0)
+#define	ZFS_PROBE1(a, c)		((void) 0)
+#define	ZFS_PROBE2(a, c, e)		((void) 0)
+#define	ZFS_PROBE3(a, c, e, g)		((void) 0)
+#define	ZFS_PROBE4(a, c, e, g, i)	((void) 0)
+#define	ZFS_SET_ERROR(err)		((void) 0)
+
+#else
+
+#if defined(HAVE_DECLARE_EVENT_CLASS)
+
+#include <sys/trace.h>
+
+/*
+ * The set-error SDT probe is extra static, in that we declare its fake
+ * function literally, rather than with the DTRACE_PROBE1() macro.  This is
+ * necessary so that SET_ERROR() can evaluate to a value, which wouldn't
+ * be possible if it required multiple statements (to declare the function
+ * and then call it).
+ *
+ * SET_ERROR() uses the comma operator so that it can be used without much
+ * additional code.  For example, "return (EINVAL);" becomes
+ * "return (SET_ERROR(EINVAL));".  Note that the argument will be evaluated
+ * twice, so it should not have side effects (e.g. something like:
+ * "return (SET_ERROR(log_error(EINVAL, info)));" would log the error twice).
+ */
+#define	SET_ERROR(err) \
+	(trace_zfs_set__error(__FILE__, __func__, __LINE__, err), err)
+
+#else
+
+#undef SET_ERROR
+#define	SET_ERROR(err) (err)
+
+#endif /* HAVE_DECLARE_EVENT_CLASS */
+
+#endif /* _KERNEL */
+
+#endif /* _SYS_SDT_H */

include/sys/zfs_context.h

@@ -66,6 +66,7 @@
 #include <sys/sunddi.h>
 #include <sys/ctype.h>
 #include <sys/disp.h>
+#include <sys/trace.h>
 #include <linux/dcache_compat.h>
 #include <linux/utsname_compat.h>
 
@@ -140,15 +141,12 @@
 #define	CE_PANIC	3	/* panic		*/
 #define	CE_IGNORE	4	/* print nothing	*/
 
-extern int aok;
-
 /*
  * ZFS debugging
  */
 
 extern void dprintf_setup(int *argc, char **argv);
-extern void __dprintf(const char *file, const char *func,
+
-    int line, const char *fmt, ...);
 extern void cmn_err(int, const char *, ...);
 extern void vcmn_err(int, const char *, va_list);
 extern void panic(const char *, ...);
@@ -156,7 +154,8 @@ extern void vpanic(const char *, va_list);
 
 #define	fm_panic	panic
 
-#ifdef __sun
+extern int aok;
+
 /*
  * DTrace SDT probes have different signatures in userland than they do in
  * kernel.  If they're being used in kernel code, re-define them out of
@@ -202,9 +201,6 @@ extern void vpanic(const char *, va_list);
  * "return (SET_ERROR(log_error(EINVAL, info)));" would log the error twice).
  */
 #define	SET_ERROR(err) (ZFS_SET_ERROR(err), err)
-#else
-#define	SET_ERROR(err) (err)
-#endif
 
 /*
  * Threads.  TS_STACK_MIN is dictated by the minimum allowed pthread stack

include/sys/zfs_debug.h

@@ -38,14 +38,6 @@ extern "C" {
 #define	FALSE 0
 #endif
 
-/*
- * ZFS debugging - Always enabled for user space builds.
- */
-
-#if !defined(ZFS_DEBUG) && !defined(_KERNEL)
-#define	ZFS_DEBUG
-#endif
-
 extern int zfs_flags;
 extern int zfs_recover;
 extern int zfs_free_leak_on_eio;
@@ -59,29 +51,15 @@ 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)
- * Always log zfs debug messages to the spl debug subsystem as SS_USER1.
+extern void __dprintf(const char *file, const char *func,
- * When the SPL is configured with debugging enabled these messages will
+    int line, const char *fmt, ...);
- * appear in the internal spl debug log, otherwise they are a no-op.
- */
-#if defined(_KERNEL)
-
-#include <spl-debug.h>
-#define	dprintf(...)                                                   \
-	if (zfs_flags & ZFS_DEBUG_DPRINTF)                             \
-		__SDEBUG(NULL, SS_USER1, SD_DPRINTF, __VA_ARGS__)
-
-/*
- * When zfs is running is user space the debugging is always enabled.
- * The messages will be printed using the __dprintf() function and
- * filtered based on the zfs_flags variable.
- */
-#else
 #define	dprintf(...) \
 	if (zfs_flags & ZFS_DEBUG_DPRINTF) \
 		__dprintf(__FILE__, __func__, __LINE__, __VA_ARGS__)
-
+#else
-#endif /* _KERNEL */
+#define	dprintf(...) ((void)0)
+#endif /* HAVE_DECLARE_EVENT_CLASS || !_KERNEL */
 
 extern void zfs_panic_recover(const char *fmt, ...);
 
@@ -93,12 +71,8 @@ typedef struct zfs_dbgmsg {
 
 extern void zfs_dbgmsg_init(void);
 extern void zfs_dbgmsg_fini(void);
-#if defined(_KERNEL) && defined(__linux__)
-#define	zfs_dbgmsg(...) dprintf(__VA_ARGS__)
-#else
 extern void zfs_dbgmsg(const char *fmt, ...);
 extern void zfs_dbgmsg_print(const char *tag);
-#endif
 
 #ifndef _KERNEL
 extern int dprintf_find_string(const char *string);

lib/libspl/include/sys/Makefile.am

@@ -33,7 +33,6 @@ libspl_HEADERS = \
 	$(top_srcdir)/lib/libspl/include/sys/param.h \
 	$(top_srcdir)/lib/libspl/include/sys/priv.h \
 	$(top_srcdir)/lib/libspl/include/sys/processor.h \
-	$(top_srcdir)/lib/libspl/include/sys/sdt.h \
 	$(top_srcdir)/lib/libspl/include/sys/stack.h \
 	$(top_srcdir)/lib/libspl/include/sys/stat.h \
 	$(top_srcdir)/lib/libspl/include/sys/stropts.h \

lib/libzpool/Makefile.am

@@ -70,6 +70,7 @@ libzpool_la_SOURCES = \
 	$(top_srcdir)/module/zfs/space_map.c \
 	$(top_srcdir)/module/zfs/space_reftree.c \
 	$(top_srcdir)/module/zfs/txg.c \
+	$(top_srcdir)/module/zfs/trace.c \
 	$(top_srcdir)/module/zfs/uberblock.c \
 	$(top_srcdir)/module/zfs/unique.c \
 	$(top_srcdir)/module/zfs/vdev.c \

module/zfs/Makefile.in

@@ -52,6 +52,7 @@ $(MODULE)-objs += @top_srcdir@/module/zfs/spa_stats.o
 $(MODULE)-objs += @top_srcdir@/module/zfs/space_map.o
 $(MODULE)-objs += @top_srcdir@/module/zfs/space_reftree.o
 $(MODULE)-objs += @top_srcdir@/module/zfs/txg.o
+$(MODULE)-objs += @top_srcdir@/module/zfs/trace.o
 $(MODULE)-objs += @top_srcdir@/module/zfs/uberblock.o
 $(MODULE)-objs += @top_srcdir@/module/zfs/unique.o
 $(MODULE)-objs += @top_srcdir@/module/zfs/vdev.o

module/zfs/spa_misc.c

@@ -238,6 +238,53 @@ static avl_tree_t spa_l2cache_avl;
 kmem_cache_t *spa_buffer_pool;
 int spa_mode_global;
 
+#ifdef ZFS_DEBUG
+/* Everything except dprintf and spa is on by default in debug builds */
+int zfs_flags = ~(ZFS_DEBUG_DPRINTF | ZFS_DEBUG_SPA);
+#else
+int zfs_flags = 0;
+#endif
+
+/*
+ * zfs_recover can be set to nonzero to attempt to recover from
+ * otherwise-fatal errors, typically caused by on-disk corruption.  When
+ * set, calls to zfs_panic_recover() will turn into warning messages.
+ * This should only be used as a last resort, as it typically results
+ * in leaked space, or worse.
+ */
+int zfs_recover = B_FALSE;
+
+/*
+ * If destroy encounters an EIO while reading metadata (e.g. indirect
+ * blocks), space referenced by the missing metadata can not be freed.
+ * Normally this causes the background destroy to become "stalled", as
+ * it is unable to make forward progress.  While in this stalled state,
+ * all remaining space to free from the error-encountering filesystem is
+ * "temporarily leaked".  Set this flag to cause it to ignore the EIO,
+ * permanently leak the space from indirect blocks that can not be read,
+ * and continue to free everything else that it can.
+ *
+ * The default, "stalling" behavior is useful if the storage partially
+ * fails (i.e. some but not all i/os fail), and then later recovers.  In
+ * this case, we will be able to continue pool operations while it is
+ * partially failed, and when it recovers, we can continue to free the
+ * space, with no leaks.  However, note that this case is actually
+ * fairly rare.
+ *
+ * Typically pools either (a) fail completely (but perhaps temporarily,
+ * e.g. a top-level vdev going offline), or (b) have localized,
+ * permanent errors (e.g. disk returns the wrong data due to bit flip or
+ * firmware bug).  In case (a), this setting does not matter because the
+ * pool will be suspended and the sync thread will not be able to make
+ * forward progress regardless.  In case (b), because the error is
+ * permanent, the best we can do is leak the minimum amount of space,
+ * which is what setting this flag will do.  Therefore, it is reasonable
+ * for this flag to normally be set, but we chose the more conservative
+ * approach of not setting it, so that there is no possibility of
+ * leaking space in the "partial temporary" failure case.
+ */
+int zfs_free_leak_on_eio = B_FALSE;
+
 /*
  * Expiration time in milliseconds. This value has two meanings. First it is
  * used to determine when the spa_deadman() logic should fire. By default the
@@ -1319,6 +1366,16 @@ spa_freeze(spa_t *spa)
 		txg_wait_synced(spa_get_dsl(spa), freeze_txg);
 }
 
+void
+zfs_panic_recover(const char *fmt, ...)
+{
+	va_list adx;
+
+	va_start(adx, fmt);
+	vcmn_err(zfs_recover ? CE_WARN : CE_PANIC, fmt, adx);
+	va_end(adx);
+}
+
 /*
  * This is a stripped-down version of strtoull, suitable only for converting
  * lowercase hexadecimal numbers that don't overflow.
@@ -1923,6 +1980,16 @@ EXPORT_SYMBOL(spa_mode);
 
 EXPORT_SYMBOL(spa_namespace_lock);
 
+module_param(zfs_flags, int, 0644);
+MODULE_PARM_DESC(zfs_flags, "Set additional debugging flags");
+
+module_param(zfs_recover, int, 0644);
+MODULE_PARM_DESC(zfs_recover, "Set to attempt to recover from fatal errors");
+
+module_param(zfs_free_leak_on_eio, int, 0644);
+MODULE_PARM_DESC(zfs_free_leak_on_eio,
+	"Set to ignore IO errors during free and permanently leak the space");
+
 module_param(zfs_deadman_synctime_ms, ulong, 0644);
 MODULE_PARM_DESC(zfs_deadman_synctime_ms, "Expiration time in milliseconds");
 

module/zfs/trace.c

@@ -2,9 +2,8 @@
  * CDDL HEADER START
  *
  * The contents of this file are subject to the terms of the
- * Common Development and Distribution License, Version 1.0 only
+ * Common Development and Distribution License (the "License").
- * (the "License").  You may not use this file except in compliance
+ * You may not use this file except in compliance with the License.
- * with the License.
  *
  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
  * or http://www.opensolaris.org/os/licensing.
@@ -20,17 +19,21 @@
  * CDDL HEADER END
  */
 /*
- * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
+ * Each Linux tracepoints subsystem must define CREATE_TRACE_POINTS in one
- * Use is subject to license terms.
+ * (and only one) C file, so this dummy file exists for that purpose.
  */
 
-#ifndef _LIBSPL_SYS_SDT_H
+#include <sys/arc_impl.h>
-#define	_LIBSPL_SYS_SDT_H
+#include <sys/vdev_impl.h>
+#include <sys/zio.h>
+#include <sys/dbuf.h>
+#include <sys/dmu_objset.h>
+#include <sys/dsl_dataset.h>
+#include <sys/dmu_tx.h>
+#include <sys/dnode.h>
+#include <sys/zfs_znode.h>
+#include <sys/zil_impl.h>
+#include <sys/zrlock.h>
 
-#define	DTRACE_PROBE(a)					((void) 0)
+#define	CREATE_TRACE_POINTS
-#define	DTRACE_PROBE1(a, b, c)				((void) 0)
+#include <sys/trace.h>
-#define	DTRACE_PROBE2(a, b, c, d, e)			((void) 0)
-#define	DTRACE_PROBE3(a, b, c, d, e, f, g)		((void) 0)
-#define	DTRACE_PROBE4(a, b, c, d, e, f, g, h, i)	((void) 0)
-
-#endif

module/zfs/zfs_debug.c

@@ -25,99 +25,22 @@
 
 #include <sys/zfs_context.h>
 
-#if !defined(_KERNEL) || !defined(__linux__)
 list_t zfs_dbgmsgs;
 int zfs_dbgmsg_size;
 kmutex_t zfs_dbgmsgs_lock;
 int zfs_dbgmsg_maxsize = 4<<20; /* 4MB */
-#endif
 
-/*
- * Enable various debugging features.
- */
-int zfs_flags = 0;
-
-/*
- * zfs_recover can be set to nonzero to attempt to recover from
- * otherwise-fatal errors, typically caused by on-disk corruption.  When
- * set, calls to zfs_panic_recover() will turn into warning messages.
- * This should only be used as a last resort, as it typically results
- * in leaked space, or worse.
- */
-int zfs_recover = B_FALSE;
-
-/*
- * If destroy encounters an EIO while reading metadata (e.g. indirect
- * blocks), space referenced by the missing metadata can not be freed.
- * Normally this causes the background destroy to become "stalled", as
- * it is unable to make forward progress.  While in this stalled state,
- * all remaining space to free from the error-encountering filesystem is
- * "temporarily leaked".  Set this flag to cause it to ignore the EIO,
- * permanently leak the space from indirect blocks that can not be read,
- * and continue to free everything else that it can.
- *
- * The default, "stalling" behavior is useful if the storage partially
- * fails (i.e. some but not all i/os fail), and then later recovers.  In
- * this case, we will be able to continue pool operations while it is
- * partially failed, and when it recovers, we can continue to free the
- * space, with no leaks.  However, note that this case is actually
- * fairly rare.
- *
- * Typically pools either (a) fail completely (but perhaps temporarily,
- * e.g. a top-level vdev going offline), or (b) have localized,
- * permanent errors (e.g. disk returns the wrong data due to bit flip or
- * firmware bug).  In case (a), this setting does not matter because the
- * pool will be suspended and the sync thread will not be able to make
- * forward progress regardless.  In case (b), because the error is
- * permanent, the best we can do is leak the minimum amount of space,
- * which is what setting this flag will do.  Therefore, it is reasonable
- * for this flag to normally be set, but we chose the more conservative
- * approach of not setting it, so that there is no possibility of
- * leaking space in the "partial temporary" failure case.
- */
-int zfs_free_leak_on_eio = B_FALSE;
-
-
-void
-zfs_panic_recover(const char *fmt, ...)
-{
-	va_list adx;
-
-	va_start(adx, fmt);
-	vcmn_err(zfs_recover ? CE_WARN : CE_PANIC, fmt, adx);
-	va_end(adx);
-}
-
-/*
- * Debug logging is enabled by default for production kernel builds.
- * The overhead for this is negligible and the logs can be valuable when
- * debugging.  For non-production user space builds all debugging except
- * logging is enabled since performance is no longer a concern.
- */
 void
 zfs_dbgmsg_init(void)
 {
-#if !defined(_KERNEL) || !defined(__linux__)
 	list_create(&zfs_dbgmsgs, sizeof (zfs_dbgmsg_t),
 	    offsetof(zfs_dbgmsg_t, zdm_node));
 	mutex_init(&zfs_dbgmsgs_lock, NULL, MUTEX_DEFAULT, NULL);
-#endif
-
-	if (zfs_flags == 0) {
-#if defined(_KERNEL)
-		zfs_flags = ZFS_DEBUG_DPRINTF;
-		spl_debug_set_mask(spl_debug_get_mask() | SD_DPRINTF);
-		spl_debug_set_subsys(spl_debug_get_subsys() | SS_USER1);
-#else
-		zfs_flags = ~ZFS_DEBUG_DPRINTF;
-#endif /* _KERNEL */
-	}
 }
 
 void
 zfs_dbgmsg_fini(void)
 {
-#if !defined(_KERNEL) || !defined(__linux__)
 	zfs_dbgmsg_t *zdm;
 
 	while ((zdm = list_remove_head(&zfs_dbgmsgs)) != NULL) {
@@ -127,25 +50,24 @@ zfs_dbgmsg_fini(void)
 	}
 	mutex_destroy(&zfs_dbgmsgs_lock);
 	ASSERT0(zfs_dbgmsg_size);
-#endif
 }
 
-#if !defined(_KERNEL) || !defined(__linux__)
 /*
- * Print these messages by running:
+ * To get this data enable the zfs__dbgmsg tracepoint as shown:
- * echo ::zfs_dbgmsg | mdb -k
  *
- * Monitor these messages by running:
+ * # Enable zfs__dbgmsg tracepoint, clear the tracepoint ring buffer
- * dtrace -qn 'zfs-dbgmsg{printf("%s\n", stringof(arg0))}'
+ * $ echo 1 > /sys/kernel/debug/tracing/events/zfs/enable
+ * $ echo 0 > /sys/kernel/debug/tracing/trace
  *
- * When used with libzpool, monitor with:
+ * # Dump the ring buffer.
- * dtrace -qn 'zfs$pid::zfs_dbgmsg:probe1{printf("%s\n", copyinstr(arg1))}'
+ * $ cat /sys/kernel/debug/tracing/trace
  */
 void
 zfs_dbgmsg(const char *fmt, ...)
 {
 	int size;
 	va_list adx;
+	char *nl;
 	zfs_dbgmsg_t *zdm;
 
 	va_start(adx, fmt);
@@ -156,13 +78,20 @@ zfs_dbgmsg(const char *fmt, ...)
 	 * There is one byte of string in sizeof (zfs_dbgmsg_t), used
 	 * for the terminating null.
 	 */
-	zdm = kmem_alloc(sizeof (zfs_dbgmsg_t) + size, KM_SLEEP);
+	zdm = kmem_alloc(sizeof (zfs_dbgmsg_t) + size, KM_PUSHPAGE);
 	zdm->zdm_timestamp = gethrestime_sec();
 
 	va_start(adx, fmt);
 	(void) vsnprintf(zdm->zdm_msg, size + 1, fmt, adx);
 	va_end(adx);
 
+	/*
+	 * Get rid of trailing newline.
+	 */
+	nl = strrchr(zdm->zdm_msg, '\n');
+	if (nl != NULL)
+		*nl = '\0';
+
 	DTRACE_PROBE1(zfs__dbgmsg, char *, zdm->zdm_msg);
 
 	mutex_enter(&zfs_dbgmsgs_lock);
@@ -180,6 +109,7 @@ zfs_dbgmsg(const char *fmt, ...)
 void
 zfs_dbgmsg_print(const char *tag)
 {
+#if !defined(_KERNEL)
 	zfs_dbgmsg_t *zdm;
 
 	(void) printf("ZFS_DBGMSG(%s):\n", tag);
@@ -188,17 +118,5 @@ zfs_dbgmsg_print(const char *tag)
 	    zdm = list_next(&zfs_dbgmsgs, zdm))
 		(void) printf("%s\n", zdm->zdm_msg);
 	mutex_exit(&zfs_dbgmsgs_lock);
+#endif /* !_KERNEL */
 }
-#endif
-
-#if defined(_KERNEL)
-module_param(zfs_flags, int, 0644);
-MODULE_PARM_DESC(zfs_flags, "Set additional debugging flags");
-
-module_param(zfs_recover, int, 0644);
-MODULE_PARM_DESC(zfs_recover, "Set to attempt to recover from fatal errors");
-
-module_param(zfs_free_leak_on_eio, int, 0644);
-MODULE_PARM_DESC(zfs_free_leak_on_eio,
-	"Set to ignore IO errors during free and permanently leak the space");
-#endif /* _KERNEL */

module/zfs/zfs_ioctl.c

@@ -247,6 +247,55 @@ static int zfs_fill_zplprops_root(uint64_t, nvlist_t *, nvlist_t *,
 int zfs_set_prop_nvlist(const char *, zprop_source_t, nvlist_t *, nvlist_t *);
 static int get_nvlist(uint64_t nvl, uint64_t size, int iflag, nvlist_t **nvp);
 
+#if defined(HAVE_DECLARE_EVENT_CLASS)
+void
+__dprintf(const char *file, const char *func, int line, const char *fmt, ...)
+{
+	const char *newfile;
+	size_t size = 4096;
+	char *buf = kmem_alloc(size, KM_PUSHPAGE);
+	char *nl;
+	va_list adx;
+
+	/*
+	 * Get rid of annoying prefix to filename.
+	 */
+	newfile = strrchr(file, '/');
+	if (newfile != NULL) {
+		newfile = newfile + 1; /* Get rid of leading / */
+	} else {
+		newfile = file;
+	}
+
+	va_start(adx, fmt);
+	(void) vsnprintf(buf, size, fmt, adx);
+	va_end(adx);
+
+	/*
+	 * Get rid of trailing newline.
+	 */
+	nl = strrchr(buf, '\n');
+	if (nl != NULL)
+		*nl = '\0';
+
+	/*
+	 * To get this data enable the zfs__dprintf trace point as shown:
+	 *
+	 * # Enable zfs__dprintf tracepoint, clear the tracepoint ring buffer
+	 * $ echo 1 > /sys/module/zfs/parameters/zfs_flags
+	 * $ echo 1 > /sys/kernel/debug/tracing/events/zfs/enable
+	 * $ echo 0 > /sys/kernel/debug/tracing/trace
+	 *
+	 * # Dump the ring buffer.
+	 * $ cat /sys/kernel/debug/tracing/trace
+	 */
+	DTRACE_PROBE4(zfs__dprintf,
+	    char *, newfile, char *, func, int, line, char *, buf);
+
+	kmem_free(buf, size);
+}
+#endif /* HAVE_DECLARE_EVENT_CLASS */
+
 static void
 history_str_free(char *buf)
 {

scripts/zfs.sh

@@ -33,7 +33,6 @@ MODULE-OPTIONS:
 
 $0 zfs="zfs_prefetch_disable=1"
 $0 zfs="zfs_prefetch_disable=1 zfs_mdcomp_disable=1"
-$0 spl="spl_debug_mask=0"
 
 EOF
 }