dm table: fix discard support

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().

Before this fix dm_table_supports_discards() would skip checking the
individual targets' 'discards_supported' flag if any one target in the
table didn't set num_discard_requests > 0.  Now the per-target
'discards_supported' flag is effective at insuring the final DM device
advertises discard support.  But, to be clear, targets that don't
support discards (!num_discard_requests) will not receive discard
requests.

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

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

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index bfe9c2333ceacecddd00d058615fc8a9f2867b1b..3909fa259f5537035ba63b277cc23a25fee3b1f0 100644 (file)
--- 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;
 
        /*
@@ -209,7 +208,6 @@ 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;
@@ -791,8 +789,9 @@ 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: ignoring discards_supported because num_discard_requests is zero.",
+                      dm_device_name(t->md), type);
 
        return 0;
 
@@ -1359,19 +1358,19 @@ 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.
         * t->devices includes internal dm devices such as mirror logs
         * so we need to use iterate_devices here, which targets
-        * supporting discard must provide.
+        * supporting discard selectively must provide.
         */
        while (i < dm_table_get_num_targets(t)) {
                ti = dm_table_get_target(t, i++);
 
+               if (!ti->num_discard_requests)
+                       continue;
+
                if (ti->discards_supported)
                        return 1;
 

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 41abc6dd481b29ec82d87289471f409dffe2bf22..aeb0fa1ccfe4ede8357441a04cc5c5f67825f5e9 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1179,7 +1179,8 @@ static int __clone_and_map_discard(struct clone_info *ci)
 
                /*
                 * Even though the device advertised discard support,
-                * reconfiguration might have changed that since the
+                * that does not mean every target supports it, and
+                * reconfiguration might also have changed that since the
                 * check was performed.
                 */
                if (!ti->num_discard_requests)