dm: allow targets to request flushes regardless of underlying device support

Allow targets to override the 'supports flush' calculation.

Set 'flush_supported' if a target needs to receive flushes regardless of
whether or not its underlying devices have support.

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

2 files changed, 9 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 2e227fbf1622..f90069029aae 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1319,6 +1319,9 @@ static bool dm_table_supports_flush(struct dm_table *t, unsigned flush)
                 if (!ti->num_flush_requests)
                         continue;
 
+                if (ti->flush_supported)
+                        return 1;
+
                 if (ti->type->iterate_devices &&
                     ti->type->iterate_devices(ti, device_flush_capable, &flush))
                         return 1;
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 8bdbbfce759a..bdd65e97a129 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -212,6 +212,12 @@ struct dm_target {
         char *error;
 
         /*
+         * Set if this target needs to receive flushes regardless of
+         * whether or not its underlying devices have support.
+         */
+        bool flush_supported:1;
+
+        /*
          * Set if this target needs to receive discards regardless of
          * whether or not its underlying devices have support.
          */