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, 14 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 985c20a4f30e..7e2ec3c05550 100644
--- a/drivers/md/dm-table.c
+++ b/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 **result, fmode_t mode,
                 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_table *t)
         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_table *t, int bdi_bits)
                                      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;
 }