dm raid: add discard support for RAID levels 1 and 10

Discard support is not enabled for RAID levels 4, 5, and 6 at this time
due to concerns about unreliable discard_zeroes_data support on some
hardware.  Otherwise, discards could cause stripe data corruption
(classic example of bad apples spoiling the bunch).

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 28 insertions, 2 deletions

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 4880b69e2e9e..030e2d6bc261 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2010-2011 Neil Brown
- * Copyright (C) 2010-2011 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2010-2014 Red Hat, Inc. All rights reserved.
  *
  * This file is released under the GPL.
  */
@@ -1150,6 +1150,27 @@ static int analyse_superblocks(struct dm_target *ti, struct raid_set *rs)
 }
 
 /*
+ * Enable/disable discard support on RAID set depending on RAID level.
+ */
+static void configure_discard_support(struct dm_target *ti, struct raid_set *rs)
+{
+        /* Assume discards not supported until after checks below. */
+        ti->discards_supported = false;
+
+        /* RAID level 4,5,6 require discard_zeroes_data for data integrity! */
+        if (rs->md.level == 4 || rs->md.level == 5 || rs->md.level == 6)
+                return; /* discard_zeroes_data cannot be trusted as reliable */
+
+        ti->discards_supported = true;
+
+        /*
+         * RAID1 and RAID10 personalities require bio splitting,
+         */
+        ti->split_discard_bios = true;
+        ti->num_discard_bios = 1;
+}
+
+/*
  * Construct a RAID4/5/6 mapping:
  * Args:
  *      <raid_type> <#raid_params> <raid_params>                \
@@ -1231,6 +1252,11 @@ static int raid_ctr(struct dm_target *ti, unsigned argc, char **argv)
         ti->private = rs;
         ti->num_flush_bios = 1;
 
+        /*
+         * Disable/enable discard support on RAID set.
+         */
+        configure_discard_support(ti, rs);
+
         mutex_lock(&rs->md.reconfig_mutex);
         ret = md_run(&rs->md);
         rs->md.in_sync = 0; /* Assume already marked dirty */
@@ -1652,7 +1678,7 @@ static void raid_resume(struct dm_target *ti)
 
 static struct target_type raid_target = {
         .name = "raid",
-        .version = {1, 5, 2},
+        .version = {1, 6, 0},
         .module = THIS_MODULE,
         .ctr = raid_ctr,
         .dtr = raid_dtr,