[PATCH RFC 3/3] dm: add support for REQ_NOWAIT and enable for target dm-linear

From: Konstantin Khlebnikov
Date: Mon Jun 01 2020 - 08:37:31 EST


Add dm target feature flag DM_TARGET_NOWAIT which tells that target
has no problem with REQ_NOWAIT.

Set limits.nowait_requests if all targets and backends handle REQ_NOWAIT.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
---
drivers/md/dm-linear.c | 5 +++--
drivers/md/dm-table.c | 3 +++
drivers/md/dm.c | 4 +++-
include/linux/device-mapper.h | 6 ++++++
4 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index e1db43446327..00774b5d7668 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -228,10 +228,11 @@ static struct target_type linear_target = {
.name = "linear",
.version = {1, 4, 0},
#ifdef CONFIG_BLK_DEV_ZONED
- .features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_ZONED_HM,
+ .features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_NOWAIT |
+ DM_TARGET_ZONED_HM,
.report_zones = linear_report_zones,
#else
- .features = DM_TARGET_PASSES_INTEGRITY,
+ .features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_NOWAIT,
#endif
.module = THIS_MODULE,
.ctr = linear_ctr,
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 0a2cc197f62b..f4610f79ebd6 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1500,12 +1500,15 @@ int dm_calculate_queue_limits(struct dm_table *table,
unsigned int zone_sectors = 0;

blk_set_stacking_limits(limits);
+ limits->nowait_requests = 1;

for (i = 0; i < dm_table_get_num_targets(table); i++) {
blk_set_stacking_limits(&ti_limits);

ti = dm_table_get_target(table, i);

+ ti_limits.nowait_requests = dm_target_supports_nowait(ti->type);
+
if (!ti->type->iterate_devices)
goto combine_limits;

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index db9e46114653..767cd4d70341 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1794,7 +1794,9 @@ static blk_qc_t dm_make_request(struct request_queue *q, struct bio *bio)
if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
dm_put_live_table(md, srcu_idx);

- if (!(bio->bi_opf & REQ_RAHEAD))
+ if (bio->bi_opf & REQ_NOWAIT)
+ bio_wouldblock_error(bio);
+ else if (!(bio->bi_opf & REQ_RAHEAD))
queue_io(md, bio);
else
bio_io_error(bio);
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index af48d9da3916..4d4af1eeeba4 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -252,6 +252,12 @@ struct target_type {
#define DM_TARGET_ZONED_HM 0x00000040
#define dm_target_supports_zoned_hm(type) ((type)->features & DM_TARGET_ZONED_HM)

+/*
+ * A target handles REQ_NOWAIT
+ */
+#define DM_TARGET_NOWAIT 0x00000080
+#define dm_target_supports_nowait(type) (!!((type)->features & DM_TARGET_NOWAIT))
+
struct dm_target {
struct dm_table *table;
struct target_type *type;