dm-stripe: limit chunk_sectors to the stripe size

Currently we use min io size as the chunk size when deciding on the limit
of atomic write size.

Using min io size is not reliable, as this may be mutated when stacking
the bottom device limits.

The block stacking limits will rely on chunk_sectors in future, so set
this value (to the chunk size).

Introduce a flag - DM_TARGET_STRIPED - and check this in
dm_set_device_limits() when setting this limit.

Signed-off-by: John Garry <[email protected]>

Author: johnpgarry

drivers/md/dm-stripe.c

@@ -466,7 +466,8 @@ static struct target_type stripe_target = {
 	.name   = "striped",
 	.version = {1, 7, 0},
 	.features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_NOWAIT |
-		    DM_TARGET_ATOMIC_WRITES | DM_TARGET_PASSES_CRYPTO,
+		    DM_TARGET_ATOMIC_WRITES | DM_TARGET_PASSES_CRYPTO |
+		    DM_TARGET_STRIPED,
 	.module = THIS_MODULE,
 	.ctr    = stripe_ctr,
 	.dtr    = stripe_dtr,

drivers/md/dm-table.c

@@ -430,6 +430,10 @@ static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
 		return 0;
 	}
 
+	/* For striped types, limit the chunk_sectors to the chunk size */
+	if (dm_target_supports_striped(ti->type))
+		limits->chunk_sectors = len >> SECTOR_SHIFT;
+
 	mutex_lock(&q->limits_lock);
 	/*
 	 * BLK_FEAT_ATOMIC_WRITES is not inherited from the bottom device in

include/linux/device-mapper.h

@@ -309,6 +309,9 @@ struct target_type {
 #define DM_TARGET_ATOMIC_WRITES		0x00000400
 #define dm_target_supports_atomic_writes(type) ((type)->features & DM_TARGET_ATOMIC_WRITES)
 
+#define DM_TARGET_STRIPED		0x00000800
+#define dm_target_supports_striped(type) ((type)->features & DM_TARGET_STRIPED)
+
 struct dm_target {
 	struct dm_table *table;
 	struct target_type *type;