xfs: Validate log space at mount time

Validate log space during log mount stage, the underlying function
will drop a warning message via syslog in critical level if the log
space is too small or too large.

[ dchinner: For CRC enable filesystems, abort the mounting of the
filesystem as mkfs should never make a log too small for the given
filesystem configuration. ]

[ dchinner: make a note of the fact that the log size limits in
block counts are in units of filesystem blocks, not basic blocks. ]

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_fs.h b/fs/xfs/xfs_fs.h
index 74b24b2..53e33c2 100644
--- a/fs/xfs/xfs_fs.h
+++ b/fs/xfs/xfs_fs.h
@@ -240,7 +240,9 @@
 
 
 /*
- * Minimum and maximum sizes need for growth checks
+ * Minimum and maximum sizes need for growth checks.
+ *
+ * Block counts are in units of filesystem blocks, not basic blocks.
  */
 #define XFS_MIN_AG_BLOCKS	64
 #define XFS_MIN_LOG_BLOCKS	512ULL