[PATCH 07/17] drbd: new disk-option disable-write-same

From: Philipp Reisner
Date: Thu Aug 24 2017 - 17:25:05 EST


From: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>

Some backend devices claim to support write-same,
but would fail actual write-same requests.

Allow to set (or toggle) whether or not DRBD tries to support write-same.

Signed-off-by: Philipp Reisner <philipp.reisner@xxxxxxxxxx>
Signed-off-by: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index ad0fcb4..c383b6c 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1236,12 +1236,18 @@ static void fixup_discard_if_not_supported(struct request_queue *q)

static void decide_on_write_same_support(struct drbd_device *device,
struct request_queue *q,
- struct request_queue *b, struct o_qlim *o)
+ struct request_queue *b, struct o_qlim *o,
+ bool disable_write_same)
{
struct drbd_peer_device *peer_device = first_peer_device(device);
struct drbd_connection *connection = peer_device->connection;
bool can_do = b ? b->limits.max_write_same_sectors : true;

+ if (can_do && disable_write_same) {
+ can_do = false;
+ drbd_info(peer_device, "WRITE_SAME disabled by config\n");
+ }
+
if (can_do && connection->cstate >= C_CONNECTED && !(connection->agreed_features & DRBD_FF_WSAME)) {
can_do = false;
drbd_info(peer_device, "peer does not support WRITE_SAME\n");
@@ -1302,6 +1308,7 @@ static void drbd_setup_queue_param(struct drbd_device *device, struct drbd_backi
struct request_queue *b = NULL;
struct disk_conf *dc;
bool discard_zeroes_if_aligned = true;
+ bool disable_write_same = false;

if (bdev) {
b = bdev->backing_bdev->bd_disk->queue;
@@ -1311,6 +1318,7 @@ static void drbd_setup_queue_param(struct drbd_device *device, struct drbd_backi
dc = rcu_dereference(device->ldev->disk_conf);
max_segments = dc->max_bio_bvecs;
discard_zeroes_if_aligned = dc->discard_zeroes_if_aligned;
+ disable_write_same = dc->disable_write_same;
rcu_read_unlock();

blk_set_stacking_limits(&q->limits);
@@ -1321,7 +1329,7 @@ static void drbd_setup_queue_param(struct drbd_device *device, struct drbd_backi
blk_queue_max_segments(q, max_segments ? max_segments : BLK_MAX_SEGMENTS);
blk_queue_segment_boundary(q, PAGE_SIZE-1);
decide_on_discard_support(device, q, b, discard_zeroes_if_aligned);
- decide_on_write_same_support(device, q, b, o);
+ decide_on_write_same_support(device, q, b, o, disable_write_same);

if (b) {
blk_queue_stack_limits(q, b);
@@ -1612,7 +1620,8 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
if (write_ordering_changed(old_disk_conf, new_disk_conf))
drbd_bump_write_ordering(device->resource, NULL, WO_BDEV_FLUSH);

- if (old_disk_conf->discard_zeroes_if_aligned != new_disk_conf->discard_zeroes_if_aligned)
+ if (old_disk_conf->discard_zeroes_if_aligned != new_disk_conf->discard_zeroes_if_aligned
+ || old_disk_conf->disable_write_same != new_disk_conf->disable_write_same)
drbd_reconsider_queue_parameters(device, device->ldev, NULL);

drbd_md_sync(device);
diff --git a/include/linux/drbd_genl.h b/include/linux/drbd_genl.h
index 2896f93..4e6d4d4 100644
--- a/include/linux/drbd_genl.h
+++ b/include/linux/drbd_genl.h
@@ -132,7 +132,8 @@ GENL_struct(DRBD_NLA_DISK_CONF, 3, disk_conf,
__flg_field_def(18, DRBD_GENLA_F_MANDATORY, disk_drain, DRBD_DISK_DRAIN_DEF)
__flg_field_def(19, DRBD_GENLA_F_MANDATORY, md_flushes, DRBD_MD_FLUSHES_DEF)
__flg_field_def(23, 0 /* OPTIONAL */, al_updates, DRBD_AL_UPDATES_DEF)
- __flg_field_def(24, 0 /* OPTIONAL */, discard_zeroes_if_aligned, DRBD_DISCARD_ZEROES_IF_ALIGNED)
+ __flg_field_def(24, 0 /* OPTIONAL */, discard_zeroes_if_aligned, DRBD_DISCARD_ZEROES_IF_ALIGNED_DEF)
+ __flg_field_def(26, 0 /* OPTIONAL */, disable_write_same, DRBD_DISABLE_WRITE_SAME_DEF)
)

GENL_struct(DRBD_NLA_RESOURCE_OPTS, 4, res_opts,
diff --git a/include/linux/drbd_limits.h b/include/linux/drbd_limits.h
index ddac684..24ae1b9 100644
--- a/include/linux/drbd_limits.h
+++ b/include/linux/drbd_limits.h
@@ -209,12 +209,18 @@
#define DRBD_MD_FLUSHES_DEF 1
#define DRBD_TCP_CORK_DEF 1
#define DRBD_AL_UPDATES_DEF 1
+
/* We used to ignore the discard_zeroes_data setting.
* To not change established (and expected) behaviour,
* by default assume that, for discard_zeroes_data=0,
* we can make that an effective discard_zeroes_data=1,
* if we only explicitly zero-out unaligned partial chunks. */
-#define DRBD_DISCARD_ZEROES_IF_ALIGNED 1
+#define DRBD_DISCARD_ZEROES_IF_ALIGNED_DEF 1
+
+/* Some backends pretend to support WRITE SAME,
+ * but fail such requests when they are actually submitted.
+ * This is to tell DRBD to not even try. */
+#define DRBD_DISABLE_WRITE_SAME_DEF 0

#define DRBD_ALLOW_TWO_PRIMARIES_DEF 0
#define DRBD_ALWAYS_ASBP_DEF 0
--
2.7.4