[PATCH] dm table: simplify discard support processing

[Mike Snitzer <snitzer@redhat.com>]

Remove 'discards_supported' from the dm_table structure.  The same
information can be easily discovered from the table's target(s) in
dm_table_supports_discards().

Also DMWARN if a target sets 'discards_supported' override but forgets
to set 'num_discard_requests'.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/md/dm-table.c |   13 ++++++-------
 1 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 367a2e0..b5bdeb3 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -54,7 +54,6 @@ struct dm_table {
 	sector_t *highs;
 	struct dm_target *targets;
 
-	unsigned discards_supported:1;
 	unsigned integrity_supported:1;
 
 	/*
@@ -207,7 +206,6 @@ int dm_table_create(struct dm_table **result, fmode_t mode,
 	INIT_LIST_HEAD(&t->devices);
 	INIT_LIST_HEAD(&t->target_callbacks);
 	atomic_set(&t->holders, 0);
-	t->discards_supported = 1;
 
 	if (!num_targets)
 		num_targets = KEYS_PER_NODE;
@@ -788,8 +786,9 @@ int dm_table_add_target(struct dm_table *t, const char *type,
 
 	t->highs[t->num_targets++] = tgt->begin + tgt->len - 1;
 
-	if (!tgt->num_discard_requests)
-		t->discards_supported = 0;
+	if (!tgt->num_discard_requests && tgt->discards_supported)
+		DMWARN("%s: %s: must set num_discard_requests if discards_supported, "
+		       "disabling discards", dm_device_name(t->md), type);
 
 	return 0;
 
@@ -1413,9 +1412,6 @@ bool dm_table_supports_discards(struct dm_table *t)
 	struct dm_target *ti;
 	unsigned i = 0;
 
-	if (!t->discards_supported)
-		return 0;
-
 	/*
 	 * Unless any target used by the table set discards_supported,
 	 * require at least one underlying device to support discards.
@@ -1426,6 +1422,9 @@ bool dm_table_supports_discards(struct dm_table *t)
 	while (i < dm_table_get_num_targets(t)) {
 		ti = dm_table_get_target(t, i++);
 
+		if (!ti->num_discard_requests)
+			return 0;
+		
 		if (ti->discards_supported)
 			return 1;