dm cache: pass a new 'critical' flag to the policies when requesting writeback work

We only allow non critical writeback if the origin is idle.  It is up
to the policy to decide what writeback work is critical.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/md/dm-cache-policy.h b/drivers/md/dm-cache-policy.h
index 5524e21e4836..6106ca3aa350 100644
--- a/drivers/md/dm-cache-policy.h
+++ b/drivers/md/dm-cache-policy.h
@@ -178,7 +178,9 @@ struct dm_cache_policy {
         int (*remove_cblock)(struct dm_cache_policy *p, dm_cblock_t cblock);
 
         /*
-         * Provide a dirty block to be written back by the core target.
+         * Provide a dirty block to be written back by the core target.  If
+         * critical_only is set then the policy should only provide work if
+         * it urgently needs it.
          *
          * Returns:
          *
@@ -186,7 +188,8 @@ struct dm_cache_policy {
          *
          * -ENODATA: no dirty blocks available
          */
-        int (*writeback_work)(struct dm_cache_policy *p, dm_oblock_t *oblock, dm_cblock_t *cblock);
+        int (*writeback_work)(struct dm_cache_policy *p, dm_oblock_t *oblock, dm_cblock_t *cblock,
+                              bool critical_only);
 
         /*
          * How full is the cache?