Document zfs_flags module parameter

Add a table describing the debugging flags that can be set in the zfs_flags
module parameter.  Also change the module_param type to 'uint' so users aren't
shown a negative value. The updated man page text is reproduced below for
convenience.

zfs_flags (int)
            Set  additional debugging flags. The following flags may be
            bitwise-or'd together.

            +-------------------------------------------------------+
            |Value   Symbolic Name                                  |
            |        Description                                    |
            +-------------------------------------------------------+
            |    1   ZFS_DEBUG_DPRINTF                              |
            |        Enable dprintf entries in the debug log.       |
            +-------------------------------------------------------+
            |    2   ZFS_DEBUG_DBUF_VERIFY *                        |
            |        Enable extra dbuf verifications.               |
            +-------------------------------------------------------+
            |    4   ZFS_DEBUG_DNODE_VERIFY *                       |
            |        Enable extra dnode verifications.              |
            +-------------------------------------------------------+
            |    8   ZFS_DEBUG_SNAPNAMES                            |
            |        Enable snapshot name verification.             |
            +-------------------------------------------------------+
            |   16   ZFS_DEBUG_MODIFY                               |
            |        Check for illegally modified ARC buffers.      |
            +-------------------------------------------------------+
            |   32   ZFS_DEBUG_SPA                                  |
            |        Enable spa_dbgmsg entries in the debug log.    |
            +-------------------------------------------------------+
            |   64   ZFS_DEBUG_ZIO_FREE                             |
            |        Enable verification of block frees.            |
            +-------------------------------------------------------+
            |  128   ZFS_DEBUG_HISTOGRAM_VERIFY                     |
            |        Enable extra spacemap histogram verifications. |
            +-------------------------------------------------------+
            * Requires debug build.

            Default value: 0.

Signed-off-by: Ned Bass <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2988

2 files changed, 39 insertions, 3 deletions

diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index 28c6e11d2..e0000a23a 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -822,9 +822,45 @@ Default value: \fB300\fR.
 \fBzfs_flags\fR (int)
 .ad
 .RS 12n
-Set additional debugging flags
+Set additional debugging flags. The following flags may be bitwise-or'd
+together.
+.sp
+.TS
+box;
+rB lB
+lB lB
+r l.
+Value	Symbolic Name
+	Description
+_
+1	ZFS_DEBUG_DPRINTF
+	Enable dprintf entries in the debug log.
+_
+2	ZFS_DEBUG_DBUF_VERIFY *
+	Enable extra dbuf verifications.
+_
+4	ZFS_DEBUG_DNODE_VERIFY *
+	Enable extra dnode verifications.
+_
+8	ZFS_DEBUG_SNAPNAMES
+	Enable snapshot name verification.
+_
+16	ZFS_DEBUG_MODIFY
+	Check for illegally modified ARC buffers.
+_
+32	ZFS_DEBUG_SPA
+	Enable spa_dbgmsg entries in the debug log.
+_
+64	ZFS_DEBUG_ZIO_FREE
+	Enable verification of block frees.
+_
+128	ZFS_DEBUG_HISTOGRAM_VERIFY
+	Enable extra spacemap histogram verifications.
+.TE
+.sp
+* Requires debug build.
 .sp
-Default value: \fB1\fR.
+Default value: \fB0\fR.
 .RE
 
 .sp
diff --git a/module/zfs/spa_misc.c b/module/zfs/spa_misc.c
index 2d16d7e06..2a2e72d5a 100644
--- a/module/zfs/spa_misc.c
+++ b/module/zfs/spa_misc.c
@@ -1980,7 +1980,7 @@ EXPORT_SYMBOL(spa_mode);
 
 EXPORT_SYMBOL(spa_namespace_lock);
 
-module_param(zfs_flags, int, 0644);
+module_param(zfs_flags, uint, 0644);
 MODULE_PARM_DESC(zfs_flags, "Set additional debugging flags");
 
 module_param(zfs_recover, int, 0644);