[PATCH 37/53] xfs_mkfs: initialize extra fields during mkfs, add docs

["Darrick J. Wong" <darrick.wong@xxxxxxxxxx>]

Document the rmapbt options to mkfs, and initialize the
extra field we added.

Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
 man/man8/mkfs.xfs.8 |   20 ++++++++++++++++++++
 mkfs/xfs_mkfs.c     |    7 ++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)


diff --git a/man/man8/mkfs.xfs.8 b/man/man8/mkfs.xfs.8
index 1fe510b..ffef906 100644
--- a/man/man8/mkfs.xfs.8
+++ b/man/man8/mkfs.xfs.8
@@ -173,6 +173,26 @@ is used, the free inode btree feature is not supported and 
is disabled.
 .BI uuid= value
 Use the given value as the filesystem UUID for the newly created filesystem.
 The default is to generate a random UUID.
+.TP
+.BI rmapbt= value
+This option enables the creation of a reverse-mapping btree index in each
+allocation group.  THe value is either 0 to disable the feature, or 1 to
+create the btree.
+.IP
+The reverse mapping btree maps filesystem blocks to the owner of the
+filesystem block.  Most of the mappings will be to an inode number and an
+offset, though there will also be mappings to filesystem metadata.  This
+secondary metadata can be used to validate the primary metadata or to
+pinpoint exactly which data has been lost when a disk error occurs.
+.IP
+By default,
+.B mkfs.xfs
+will not create reverse mapping btrees.  This feature is only available
+for filesystems created with the (default)
+.B \-m crc=1
+option set. When the option
+.B \-m crc=0
+is used, the reverse mapping btree feature is not supported and is disabled.
 .RE
 .TP
 .BI \-d " data_section_options"
diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index b2b087f..15a3866 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -3016,6 +3016,7 @@ _("size %s specified for log subvolume is too large, 
maximum is %lld blocks\n"),
                        rrec->rm_startblock = 0;
                        rrec->rm_blockcount = cpu_to_be32(XFS_BNO_BLOCK(mp));
                        rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_FS);
+                       rrec->rm_offset = 0;
                        be16_add_cpu(&block->bb_numrecs, 1);
 
                        /* account freespace btree root blocks */
@@ -3023,6 +3024,7 @@ _("size %s specified for log subvolume is too large, 
maximum is %lld blocks\n"),
                        rrec->rm_startblock = cpu_to_be32(XFS_BNO_BLOCK(mp));
                        rrec->rm_blockcount = cpu_to_be32(2);
                        rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_AG);
+                       rrec->rm_offset = 0;
                        be16_add_cpu(&block->bb_numrecs, 1);
 
                        /* account inode btree root blocks */
@@ -3031,6 +3033,7 @@ _("size %s specified for log subvolume is too large, 
maximum is %lld blocks\n"),
                        rrec->rm_blockcount = cpu_to_be32(XFS_RMAP_BLOCK(mp) -
                                                        XFS_IBT_BLOCK(mp));
                        rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_INOBT);
+                       rrec->rm_offset = 0;
                        be16_add_cpu(&block->bb_numrecs, 1);
 
                        /* account for rmap btree root */
@@ -3038,6 +3041,7 @@ _("size %s specified for log subvolume is too large, 
maximum is %lld blocks\n"),
                        rrec->rm_startblock = cpu_to_be32(XFS_RMAP_BLOCK(mp));
                        rrec->rm_blockcount = cpu_to_be32(1);
                        rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_AG);
+                       rrec->rm_offset = 0;
                        be16_add_cpu(&block->bb_numrecs, 1);
 
                        /* account for the log space */
@@ -3047,6 +3051,7 @@ _("size %s specified for log subvolume is too large, 
maximum is %lld blocks\n"),
                                                XFS_FSB_TO_AGBNO(mp, logstart));
                                rrec->rm_blockcount = cpu_to_be32(logblocks);
                                rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_LOG);
+                               rrec->rm_offset = 0;
                                be16_add_cpu(&block->bb_numrecs, 1);
                        }
 
@@ -3290,7 +3295,7 @@ usage( void )
 {
        fprintf(stderr, _("Usage: %s\n\
 /* blocksize */                [-b log=n|size=num]\n\
-/* metadata */         [-m crc=0|1,finobt=0|1,uuid=xxx]\n\
+/* metadata */         [-m crc=0|1,finobt=0|1,uuid=xxx,rmapbt=0|1]\n\
 /* data subvol */      [-d agcount=n,agsize=n,file,name=xxx,size=num,\n\
                            (sunit=value,swidth=value|su=num,sw=num|noalign),\n\
                            sectlog=n|sectsize=num\n\