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Date: Thu, 13 May 2010 01:02:53 -0400
From: Mike Snitzer <snitzer@...hat.com>
To: dm-devel@...hat.com
Cc: Kiyoshi Ueda <k-ueda@...jp.nec.com>,
Nikanth Karthikesan <knikanth@...e.de>,
linux-kernel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>,
"Jun'ichi Nomura" <j-nomura@...jp.nec.com>,
Vivek Goyal <vgoyal@...hat.com>
Subject: [RFC PATCH 3/2] dm: bio-based device must not register elevator in
sysfs
Properly clear io scheduler state from sysfs if transitioning from a
request-based table back to bio-based. Unregister the elevator from
sysfs (removes 'iosched/') and have the 'scheduler' sysfs attribute
properly report "none" for bio-based DM.
Adjust elv_iosched_show() to return "none" if !blk_queue_stackable.
This allows the block layer to take bio-based DM into consideration.
These changes address the following (albeit obscure) corner-case:
# dmsetup create --notable bio-based
# echo "0 100 multipath ..." | dmsetup load bio-based
# echo "0 100 linear ..." | dmsetup load bio-based
# dmsetup resume bio-based
# ls /sys/block/dm-0/queue/
... iosched ...
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
---
block/elevator.c | 2 +-
drivers/md/dm-table.c | 1 +
drivers/md/dm.c | 41 ++++++++++++++++++++++++++++++++++++++---
drivers/md/dm.h | 1 +
4 files changed, 41 insertions(+), 4 deletions(-)
diff --git a/block/elevator.c b/block/elevator.c
index 6ec9137..168112e 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1088,7 +1088,7 @@ ssize_t elv_iosched_show(struct request_queue *q, char *name)
struct elevator_type *__e;
int len = 0;
- if (!q->elevator)
+ if (!q->elevator || !blk_queue_stackable(q))
return sprintf(name, "none\n");
elv = e->elevator_type;
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 64a8578..dec8295 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -803,6 +803,7 @@ int dm_table_set_type(struct dm_table *t)
if (bio_based) {
/* We must use this table as bio-based */
t->type = DM_TYPE_BIO_BASED;
+ dm_clear_request_based_queue(t->md);
return 0;
}
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b2171be..08a4745 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1957,9 +1957,9 @@ bad_module_get:
int dm_init_request_based_queue(struct mapped_device *md)
{
struct request_queue *q = NULL;
+ int register_queue = 0;
- if (!md->queue)
- return 0;
+ BUG_ON(!md->queue);
/*
* Avoid re-initializing the queue (and leaking the existing
@@ -1973,9 +1973,22 @@ int dm_init_request_based_queue(struct mapped_device *md)
md->queue = q;
md->saved_make_request_fn = md->queue->make_request_fn;
blk_queue_make_request(md->queue, dm_request);
- elv_register_queue(md->queue);
+ register_queue = 1;
+ } else if (!md->queue->request_fn) {
+ /*
+ * Handle corner-case where bio-based table was cleared
+ * and requested-based table was loaded in its place.
+ * - re-instate the ->request_fn that was cleared
+ * by dm_clear_request_based_queue().
+ * - register the queue's 'iosched/' sysfs attributes
+ */
+ md->queue->request_fn = dm_request_fn;
+ register_queue = 1;
}
+ if (register_queue)
+ elv_register_queue(md->queue);
+
/*
* Request-based dm devices cannot be stacked on top of bio-based dm
* devices. The type of this dm device has not been decided yet.
@@ -1996,6 +2009,28 @@ int dm_init_request_based_queue(struct mapped_device *md)
return 1;
}
+void dm_clear_request_based_queue(struct mapped_device *md)
+{
+ BUG_ON(!md->queue);
+
+ if (!md->queue->elevator)
+ return; /* already bio-based so return */
+
+ /*
+ * Clear ->request_fn, treat NULL as a flag to indicate a
+ * bio-based table was loaded after a request-based table.
+ */
+ md->queue->request_fn = NULL;
+
+ /*
+ * Unregister the request-based queue's elevator from sysfs.
+ * NOTE: md->queue doesn't have the QUEUE_FLAG_STACKABLE flag
+ * set so elv_iosched_show() will report the allocated queue's
+ * type as "none" through the 'scheduler' sysfs attribute.
+ */
+ elv_unregister_queue(md->queue);
+}
+
static void unlock_fs(struct mapped_device *md);
static void free_dev(struct mapped_device *md)
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 489feba..95aec64 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -114,6 +114,7 @@ struct kobject *dm_kobject(struct mapped_device *md);
struct mapped_device *dm_get_from_kobject(struct kobject *kobj);
int dm_init_request_based_queue(struct mapped_device *md);
+void dm_clear_request_based_queue(struct mapped_device *md);
/*
* Targets for linear and striped mappings
--
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