From: NeilBrown <neilb@suse.de>

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>

---
drivers/md/dm-raid.c          |   18 ++++++++++++++++--
 drivers/md/dm-table.c         |   14 ++++++++++++++
 include/linux/device-mapper.h |   11 +++++++++++
 2 files changed, 25 insertions(+)

Index: linux-2.6.37/drivers/md/dm-table.c
===================================================================
--- linux-2.6.37.orig/drivers/md/dm-table.c
+++ linux-2.6.37/drivers/md/dm-table.c
@@ -71,6 +71,8 @@ struct dm_table {
 	void *event_context;
 
 	struct dm_md_mempools *mempools;
+
+	struct list_head target_callbacks;
 };
 
 /*
@@ -204,6 +206,7 @@ int dm_table_create(struct dm_table **re
 		return -ENOMEM;
 
 	INIT_LIST_HEAD(&t->devices);
+	INIT_LIST_HEAD(&t->target_callbacks);
 	atomic_set(&t->holders, 0);
 	t->discards_supported = 1;
 
@@ -1225,10 +1228,17 @@ int dm_table_resume_targets(struct dm_ta
 	return 0;
 }
 
+void dm_table_add_target_callbacks(struct dm_table *t, struct dm_target_callbacks *cb)
+{
+	list_add(&cb->list, &t->target_callbacks);
+}
+EXPORT_SYMBOL_GPL(dm_table_add_target_callbacks);
+
 int dm_table_any_congested(struct dm_table *t, int bdi_bits)
 {
 	struct dm_dev_internal *dd;
 	struct list_head *devices = dm_table_get_devices(t);
+	struct dm_target_callbacks *cb;
 	int r = 0;
 
 	list_for_each_entry(dd, devices, list) {
@@ -1243,6 +1253,10 @@ int dm_table_any_congested(struct dm_tab
 				     bdevname(dd->dm_dev.bdev, b));
 	}
 
+	list_for_each_entry(cb, &t->target_callbacks, list)
+		if (cb->congested_fn)
+			r |= cb->congested_fn(cb, bdi_bits);
+
 	return r;
 }
 
Index: linux-2.6.37/include/linux/device-mapper.h
===================================================================
--- linux-2.6.37.orig/include/linux/device-mapper.h
+++ linux-2.6.37/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 
 			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);