dm: introduce target callbacks and congestion callback

DM currently implements congestion checking by checking on congestion
in each component device.  For raid456 we need to also check if the
stripe cache is congested.

Add per-target congestion checker callback support.

Extending the target_callbacks structure with additional callback
functions allows for establishing multiple callbacks per-target (a
callback is also needed for unplug).

Cc: linux-raid@vger.kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 2970022..4b1c63d 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -193,6 +193,12 @@ struct dm_target {
 	char *error;
 };
 
+/* Each target can link one of these into the table */
+struct dm_target_callbacks {
+	struct list_head list;
+	int (*congested_fn) (struct dm_target_callbacks *, int);
+};
+
 int dm_register_target(struct target_type *t);
 void dm_unregister_target(struct target_type *t);
 
@@ -269,6 +275,11 @@ int dm_table_add_target(struct dm_table *t, const char *type,
 			sector_t start, sector_t len, char *params);
 
 /*
+ * Target_ctr should call this if it needs to add any callbacks.
+ */
+void dm_table_add_target_callbacks(struct dm_table *t, struct dm_target_callbacks *cb);
+
+/*
  * Finally call this to make the table ready for use.
  */
 int dm_table_complete(struct dm_table *t);