md/bitmap: prepare for storing write-intent-bitmap via dm-dirty-log.

This allows md/raid5 to fully work as a dm target.

Normally md uses a 'filemap' which contains a list of pages of bits
each of which may be written separately.
dm-log uses and all-or-nothing approach to writing the log, so
when using a dm-log, ->filemap is NULL and the flags normally stored
in filemap_attr are stored in ->logattrs instead.



Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/md/md.h b/drivers/md/md.h
index 0a850780b5d1..cccbadb31bae 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -317,6 +317,11 @@ struct mddev_s
                                                          * hot-adding a bitmap.  It should
                                                          * eventually be settable by sysfs.
                                                          */
+                /* When md is serving under dm, it might use a
+                 * dirty_log to store the bits.
+                 */
+                struct dm_dirty_log *log;
+
                 struct mutex            mutex;
                 unsigned long           chunksize;
                 unsigned long           daemon_sleep; /* how many jiffies between updates? */