dm stripe: expose correct io hints

Set sensible I/O hints for striped DM devices in the topology
infrastructure added for 2.6.31 for userspace tools to
obtain via sysfs.

Add .io_hints to 'struct target_type' to allow the I/O hints portion
(io_min and io_opt) of the 'struct queue_limits' to be set by each
target and implement this for dm-stripe.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-stripe.c

@@ -329,9 +329,19 @@ static int stripe_iterate_devices(struct dm_target *ti,
 	return ret;
 }
 
+static void stripe_io_hints(struct dm_target *ti,
+			    struct queue_limits *limits)
+{
+	struct stripe_c *sc = ti->private;
+	unsigned chunk_size = (sc->chunk_mask + 1) << 9;
+
+	blk_limits_io_min(limits, chunk_size);
+	limits->io_opt = chunk_size * sc->stripes;
+}
+
 static struct target_type stripe_target = {
 	.name   = "striped",
-	.version = {1, 2, 0},
+	.version = {1, 3, 0},
 	.module = THIS_MODULE,
 	.ctr    = stripe_ctr,
 	.dtr    = stripe_dtr,
@@ -339,6 +349,7 @@ static struct target_type stripe_target = {
 	.end_io = stripe_end_io,
 	.status = stripe_status,
 	.iterate_devices = stripe_iterate_devices,
+	.io_hints = stripe_io_hints,
 };
 
 int __init dm_stripe_init(void)

drivers/md/dm-table.c

@@ -1007,6 +1007,10 @@ int dm_calculate_queue_limits(struct dm_table *table,
 		ti->type->iterate_devices(ti, dm_set_device_limits,
 					  &ti_limits);
 
+		/* Set I/O hints portion of queue limits */
+		if (ti->type->io_hints)
+			ti->type->io_hints(ti, &ti_limits);
+
 		/*
 		 * Check each device area is consistent with the target's
 		 * overall queue limits.

include/linux/device-mapper.h

@@ -91,6 +91,9 @@ typedef int (*dm_iterate_devices_fn) (struct dm_target *ti,
 				      iterate_devices_callout_fn fn,
 				      void *data);
 
+typedef void (*dm_io_hints_fn) (struct dm_target *ti,
+				struct queue_limits *limits);
+
 /*
  * Returns:
  *    0: The target can handle the next I/O immediately.
@@ -151,6 +154,7 @@ struct target_type {
 	dm_merge_fn merge;
 	dm_busy_fn busy;
 	dm_iterate_devices_fn iterate_devices;
+	dm_io_hints_fn io_hints;
 
 	/* For internal device-mapper use. */
 	struct list_head list;