[PATCH 7/5] xfs_repair.8: document dirty log conditions

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

Add a section describing what is a dirty log, why xfs_repair won't touch
such things, and what one can do to clear the condition and check the
filesystem.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 man/man8/xfs_repair.8 |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/man/man8/xfs_repair.8 b/man/man8/xfs_repair.8
index 1b4d9e3..e4ca88e 100644
--- a/man/man8/xfs_repair.8
+++ b/man/man8/xfs_repair.8
@@ -510,6 +510,25 @@ will return a status of 1 if filesystem corruption was detected and
 0 if no filesystem corruption was detected.
 .B xfs_repair
 run without the \-n option will always return a status code of 0.
+.SH DIRTY LOGS
+Due to the design of the XFS log, a dirty log can only be replayed on a
+machine having the same CPU architecture as the machine which was
+writing to the log.
+xfs_repair cannot replay a dirty log and will return a status code of 2
+when it detects a dirty log.
+.PP
+In this situation, the log can be replayed by mounting and immediately
+unmounting the filesystem on the same class of machine that crashed.
+Please make sure that the machine's hardware is reliable before
+replaying to avoid compounding the problems.
+.PP
+If mounting fails, the log can be erased by running xfs_repair with the
+-L option.
+All metadata updates in progress at the time of the crash will be lost,
+which may cause significant filesystem damage.
+This should
+.B only
+be used as a last resort.
 .SH BUGS
 The filesystem to be checked and repaired must have been
 unmounted cleanly using normal system administration procedures