[PATCH 1/4] dm: Introduce zone append support control

[Damien Le Moal]

Add the boolean field zone_append_not_supported to the dm_target
structure to allow a target implementing a zoned block device to
explicitly opt out from zone append (REQ_OP_ZONE_APPEND) operations
support. When set to true by the target constructor, the target device
queue limit max_zone_append_sectors is set to 0 in
dm_table_set_restrictions() so that users of the target (e.g. file
systems) can detect that the device cannot process zone append
operations.

Detection for the target support of zone append is done similarly to
the detection for other device features such as secure erase, using a
helper function. For zone append, the function
dm_table_supports_zone_append() is defined if CONFIG_BLK_DEV_ZONED is
enabled.

Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
---
 drivers/md/dm-table.c         | 41 +++++++++++++++++++++++++++++++++++
 include/linux/device-mapper.h |  6 +++++
 2 files changed, 47 insertions(+)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index e5f0f1703c5d..9efd7a0ee27e 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1999,6 +1999,37 @@ static int device_requires_stable_pages(struct dm_target *ti,
 	return blk_queue_stable_writes(q);
 }
 
+#ifdef CONFIG_BLK_DEV_ZONED
+static int device_not_zone_append_capable(struct dm_target *ti,
+					  struct dm_dev *dev, sector_t start,
+					  sector_t len, void *data)
+{
+	struct request_queue *q = bdev_get_queue(dev->bdev);
+
+	return !blk_queue_is_zoned(q) ||
+		!q->limits.max_zone_append_sectors;
+}
+
+static bool dm_table_supports_zone_append(struct dm_table *t)
+{
+	struct dm_target *ti;
+	unsigned int i;
+
+	for (i = 0; i < dm_table_get_num_targets(t); i++) {
+		ti = dm_table_get_target(t, i);
+
+		if (ti->zone_append_not_supported)
+			return false;
+
+		if (!ti->type->iterate_devices ||
+		    ti->type->iterate_devices(ti, device_not_zone_append_capable, NULL))
+			return false;
+	}
+
+	return true;
+}
+#endif
+
 void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 			       struct queue_limits *limits)
 {
@@ -2091,6 +2122,16 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 	if (blk_queue_is_zoned(q)) {
 		WARN_ON_ONCE(queue_is_mq(q));
 		q->nr_zones = blkdev_nr_zones(t->md->disk);
+
+		/*
+		 * All zoned devices support zone append by default. However,
+		 * some zoned targets (e.g. dm-crypt) cannot support this
+		 * operation. Check here if the target indicated the lack of
+		 * support for zone append and set max_zone_append_sectors to 0
+		 * in that case so that users (e.g. an FS) can detect this fact.
+		 */
+		if (!dm_table_supports_zone_append(t))
+			q->limits.max_zone_append_sectors = 0;
 	}
 #endif
 
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 5c641f930caf..4da699add262 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -361,6 +361,12 @@ struct dm_target {
 	 * Set if we need to limit the number of in-flight bios when swapping.
 	 */
 	bool limit_swap_bios:1;
+
+	/*
+	 * Set if this target is a zoned device that cannot accept
+	 * zone append operations.
+	 */
+	bool zone_append_not_supported:1;
 };
 
 void *dm_per_bio_data(struct bio *bio, size_t data_size);
-- 
2.30.2