[PATCH v3 0/2] dm: restrict conflicting table loads and improve queue initialization

[PATCH v3 0/2] dm: restrict conflicting table loads and improve queue initialization

[Mike Snitzer]

A mapped_device now has a specific immutable type (md->type) that is
set during the initial table_load (see: patch 1/2).

The DM device's request_queue will only have an elevator allocated and
exposed via sysfs if it is request-based (see: patch 2/2).

Please see the individual patch headers for more details.
(Kiyoshi, if you approve please reply with your "Acked-by" :)

This patchset is based on agk's DM "editing" tree:
http://www.kernel.org/pub/linux/kernel/people/agk/patches/2.6/editing/
(apply all patches listed in the series file up to NEXT_PATCHES_END)

This patchset also depends on the following linux-2.6-block.git
'for-linus' branch commits:
01effb0 block: allow initialization of previously allocated request_queue
e36f724 block: Adjust elv_iosched_show to return "none" for bio-based DM

I've made a full quilt series available here (builds on 2.6.34):
http://people.redhat.com/msnitzer/patches/dm-queue-init/latest/

A monolithic patch is also available here:
http://people.redhat.com/msnitzer/patches/dm-queue-init/latest/monolithic.patch

I welcome all comments/review.

v3 changes:
- reduce table_load's md->type_lock protected critical section
- only call dm_setup_md_queue on first table load
  - simplified dm_setup_md_queue as a result
- use existing DM_TYPE_* definitions instead of duplicating them
- eliminate overly verbose comments as the code speaks for itself much
  more clearly

v2 changes:
- remove do_resume and table_clear interlock
- rebase to agk's latest "editing" tree
- drop the dm_get_verified_mdptr and find_device_noinit patches that
  were at the end of v1; can revisit that code duplication cleanup later

Mike Snitzer (2):
  dm: prevent table type changes after initial table load
  dm: only initialize full request_queue for request-based device

 drivers/md/dm-ioctl.c |   24 +++++++++
 drivers/md/dm.c       |  131 +++++++++++++++++++++++++++++++++++++------------
 drivers/md/dm.h       |    7 +++
 3 files changed, 130 insertions(+), 32 deletions(-)

[PATCH v3 1/2] dm: prevent table type changes after initial table load

[Mike Snitzer]

Before table_load() stages an inactive table atomically check if its
type conflicts with a previously established device type (md->type).

Introduce 'type_lock' in mapped_device structure and use it to protect
md->type access.  table_load() sets md->type without concern for:
- another table_load() racing to set conflicting md->type.
- do_resume() making a conflicting table live.

Allowed transitions:
DM_TYPE_NONE => DM_TYPE_BIO_BASED
DM_TYPE_NONE => DM_TYPE_REQUEST_BASED

Once a table load occurs the DM device's type is completely immutable.

This prevents a table reload from switching the inactive table directly
to a conflicting type (even if the table is explicitly cleared before
load).

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/md/dm-ioctl.c |   15 +++++++++++++++
 drivers/md/dm.c       |   40 +++++++++++++++++++++++++++++++++-------
 drivers/md/dm.h       |    5 +++++
 3 files changed, 53 insertions(+), 7 deletions(-)

Index: linux-2.6/drivers/md/dm-ioctl.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-ioctl.c
+++ linux-2.6/drivers/md/dm-ioctl.c
@@ -1176,6 +1176,21 @@ static int table_load(struct dm_ioctl *p
 		goto out;
 	}
 
+	/* Protect md->type against concurrent table loads. */
+	dm_lock_md_type(md);
+	if (dm_get_md_type(md) == DM_TYPE_NONE) {
+		/* initial table load, set md's type based on table's type */
+		dm_set_md_type(md, t);
+	} else if (dm_get_md_type(md) != dm_table_get_type(t)) {
+		DMWARN("can't change device type after initial table load.");
+		dm_table_destroy(t);
+		dm_unlock_md_type(md);
+		r = -EINVAL;
+		goto out;
+	}
+	dm_unlock_md_type(md);
+
+	/* stage inactive table */
 	down_write(&_hash_lock);
 	hc = dm_get_mdptr(md);
 	if (!hc || hc->md != md) {
Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c
+++ linux-2.6/drivers/md/dm.c
@@ -123,6 +123,10 @@ struct mapped_device {
 	unsigned long flags;
 
 	struct request_queue *queue;
+	unsigned type;
+	/* Protect type against concurrent access. */
+	struct mutex type_lock;
+
 	struct gendisk *disk;
 	char name[16];
 
@@ -1874,8 +1878,10 @@ static struct mapped_device *alloc_dev(i
 	if (r < 0)
 		goto bad_minor;
 
+	md->type = DM_TYPE_NONE;
 	init_rwsem(&md->io_lock);
 	mutex_init(&md->suspend_lock);
+	mutex_init(&md->type_lock);
 	spin_lock_init(&md->deferred_lock);
 	spin_lock_init(&md->barrier_error_lock);
 	rwlock_init(&md->map_lock);
@@ -2128,6 +2134,33 @@ int dm_create(int minor, struct mapped_d
 	return 0;
 }
 
+/*
+ * Functions to manage md->type.
+ * All are required to hold md->type_lock.
+ */
+void dm_lock_md_type(struct mapped_device *md)
+{
+	mutex_lock(&md->type_lock);
+}
+
+void dm_unlock_md_type(struct mapped_device *md)
+{
+	mutex_unlock(&md->type_lock);
+}
+
+void dm_set_md_type(struct mapped_device *md, struct dm_table* t)
+{
+	if (dm_table_request_based(t))
+		md->type = DM_TYPE_REQUEST_BASED;
+	else
+		md->type = DM_TYPE_BIO_BASED;
+}
+
+unsigned dm_get_md_type(struct mapped_device *md)
+{
+	return md->type;
+}
+
 static struct mapped_device *dm_find_md(dev_t dev)
 {
 	struct mapped_device *md;
@@ -2403,13 +2436,6 @@ struct dm_table *dm_swap_table(struct ma
 		goto out;
 	}
 
-	/* cannot change the device type, once a table is bound */
-	if (md->map &&
-	    (dm_table_get_type(md->map) != dm_table_get_type(table))) {
-		DMWARN("can't change the device type after a table is bound");
-		goto out;
-	}
-
 	map = __bind(md, table, &limits);
 
 out:
Index: linux-2.6/drivers/md/dm.h
===================================================================
--- linux-2.6.orig/drivers/md/dm.h
+++ linux-2.6/drivers/md/dm.h
@@ -66,6 +66,11 @@ int dm_table_alloc_md_mempools(struct dm
 void dm_table_free_md_mempools(struct dm_table *t);
 struct dm_md_mempools *dm_table_get_md_mempools(struct dm_table *t);
 
+void dm_lock_md_type(struct mapped_device *md);
+void dm_unlock_md_type(struct mapped_device *md);
+void dm_set_md_type(struct mapped_device *md, struct dm_table* t);
+unsigned dm_get_md_type(struct mapped_device *md);
+
 /*
  * To check the return value from dm_table_find_target().
  */

Re: [PATCH v3 1/2] dm: prevent table type changes after initial table load

[Kiyoshi Ueda]

Hi Mike,

Some small comments below.

For others,
Acked-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>

On 05/25/2010 11:43 PM +0900, Mike Snitzer wrote:
> @@ -1176,6 +1176,21 @@ static int table_load(struct dm_ioctl *p
>  		goto out;
>  	}
>  
> +	/* Protect md->type against concurrent table loads. */
> +	dm_lock_md_type(md);
> +	if (dm_get_md_type(md) == DM_TYPE_NONE) {
> +		/* initial table load, set md's type based on table's type */
> +		dm_set_md_type(md, t);

                dm_set_md_type(md, dm_table_get_type(t));

Although I don't impose this interface, I feel it is straightforward
for this function.  Then, dm_set_md_type() just set the type in md->type;

	void dm_set_md_type(struct mapped_device *md, unsigned type)
	{
		md->type = type;
	}

If you take the current interface, I feel it's not normal coding style;

> +void dm_set_md_type(struct mapped_device *md, struct dm_table* t)

Should be "dm_table *t" instead of "dm_table* t".


> @@ -66,6 +66,11 @@ int dm_table_alloc_md_mempools(struct dm
>  void dm_table_free_md_mempools(struct dm_table *t);
>  struct dm_md_mempools *dm_table_get_md_mempools(struct dm_table *t);
>  
> +void dm_lock_md_type(struct mapped_device *md);
> +void dm_unlock_md_type(struct mapped_device *md);
> +void dm_set_md_type(struct mapped_device *md, struct dm_table* t);

The same coding style here.

Thanks,
Kiyoshi Ueda

Re: [PATCH v3 1/2] dm: prevent table type changes after initial table load

[Mike Snitzer]

On Wed, May 26, 2010 at 11:11 PM, Kiyoshi Ueda <k-ueda@ct.jp.nec.com> wrote:
> Hi Mike,
>
> Some small comments below.
>
> For others,
> Acked-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
>
> On 05/25/2010 11:43 PM +0900, Mike Snitzer wrote:
>> @@ -1176,6 +1176,21 @@ static int table_load(struct dm_ioctl *p
>>               goto out;
>>       }
>>
>> +     /* Protect md->type against concurrent table loads. */
>> +     dm_lock_md_type(md);
>> +     if (dm_get_md_type(md) == DM_TYPE_NONE) {
>> +             /* initial table load, set md's type based on table's type */
>> +             dm_set_md_type(md, t);
>
>                dm_set_md_type(md, dm_table_get_type(t));
>
> Although I don't impose this interface, I feel it is straightforward
> for this function.  Then, dm_set_md_type() just set the type in md->type;
>
>        void dm_set_md_type(struct mapped_device *md, unsigned type)
>        {
>                md->type = type;
>        }

Looks good, I'll change it as you suggest.

Thanks,
Mike

[PATCH v3 2/2 "v10"] dm: only initialize full request_queue for request-based device

[Mike Snitzer]

Allocate a minimalist request_queue structure initially (needed for both
bio and request-based DM).  A bio-based DM device no longer defaults to
having a fully initialized request_queue (request_fn, elevator, etc).
So bio-based DM devices no longer register elevator sysfs attributes
('iosched/' tree or 'scheduler' other than "none").

Initialization of a full request_queue (request_fn, elevator, etc) is
deferred until it is known that the DM device is request-based -- at the
end of the table load sequence.

Factor DM device's request_queue initialization:
- common to both request-based and bio-based into dm_init_md_queue().
- specific to request-based into dm_init_request_based_queue().

md->type_lock is also used to protect md->queue during table_load().
md->queue is setup without concern for:
- another table_load() racing to setup conflicting queue state.
- do_resume() making a conflicting table live.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/md/dm-ioctl.c |   11 +++++
 drivers/md/dm.c       |   93 ++++++++++++++++++++++++++++++++++++--------------
 drivers/md/dm.h       |    2 +
 3 files changed, 79 insertions(+), 27 deletions(-)

Index: linux-2.6/drivers/md/dm-ioctl.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-ioctl.c
+++ linux-2.6/drivers/md/dm-ioctl.c
@@ -1176,11 +1176,20 @@ static int table_load(struct dm_ioctl *p
 		goto out;
 	}
 
-	/* Protect md->type against concurrent table loads. */
+	/* Protect md->type and md->queue against concurrent table loads. */
 	dm_lock_md_type(md);
 	if (dm_get_md_type(md) == DM_TYPE_NONE) {
 		/* initial table load, set md's type based on table's type */
 		dm_set_md_type(md, t);
+
+		/* setup md->queue to reflect md's type (may block) */
+		r = dm_setup_md_queue(md);
+		if (r) {
+			DMWARN("unable to setup device queue for this table.");
+			dm_table_destroy(t);
+			dm_unlock_md_type(md);
+			goto out;
+		}
 	} else if (dm_get_md_type(md) != dm_table_get_type(t)) {
 		DMWARN("can't change device type after initial table load.");
 		dm_table_destroy(t);
Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c
+++ linux-2.6/drivers/md/dm.c
@@ -124,7 +124,7 @@ struct mapped_device {
 
 	struct request_queue *queue;
 	unsigned type;
-	/* Protect type against concurrent access. */
+	/* Protect queue and type against concurrent access. */
 	struct mutex type_lock;
 
 	struct gendisk *disk;
@@ -1853,6 +1853,28 @@ static const struct block_device_operati
 static void dm_wq_work(struct work_struct *work);
 static void dm_rq_barrier_work(struct work_struct *work);
 
+static void dm_init_md_queue(struct mapped_device *md)
+{
+	/*
+	 * 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.
+	 * The type is decided at the first table loading time.
+	 * To prevent problematic device stacking, clear the queue flag
+	 * for request stacking support until then.
+	 *
+	 * This queue is new, so no concurrency on the queue_flags.
+	 */
+	queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
+
+	md->queue->queuedata = md;
+	md->queue->backing_dev_info.congested_fn = dm_any_congested;
+	md->queue->backing_dev_info.congested_data = md;
+	blk_queue_make_request(md->queue, dm_request);
+	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
+	md->queue->unplug_fn = dm_unplug_all;
+	blk_queue_merge_bvec(md->queue, dm_merge_bvec);
+}
+
 /*
  * Allocate and initialise a blank device with a given minor.
  */
@@ -1892,34 +1914,11 @@ static struct mapped_device *alloc_dev(i
 	INIT_LIST_HEAD(&md->uevent_list);
 	spin_lock_init(&md->uevent_lock);
 
-	md->queue = blk_init_queue(dm_request_fn, NULL);
+	md->queue = blk_alloc_queue(GFP_KERNEL);
 	if (!md->queue)
 		goto bad_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,
-	 * although we initialized the queue using blk_init_queue().
-	 * The type is decided at the first table loading time.
-	 * To prevent problematic device stacking, clear the queue flag
-	 * for request stacking support until then.
-	 *
-	 * This queue is new, so no concurrency on the queue_flags.
-	 */
-	queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
-	md->saved_make_request_fn = md->queue->make_request_fn;
-	md->queue->queuedata = md;
-	md->queue->backing_dev_info.congested_fn = dm_any_congested;
-	md->queue->backing_dev_info.congested_data = md;
-	blk_queue_make_request(md->queue, dm_request);
-	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
-	md->queue->unplug_fn = dm_unplug_all;
-	blk_queue_merge_bvec(md->queue, dm_merge_bvec);
-	blk_queue_softirq_done(md->queue, dm_softirq_done);
-	blk_queue_prep_rq(md->queue, dm_prep_fn);
-	blk_queue_lld_busy(md->queue, dm_lld_busy);
-	blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH,
-			  dm_rq_prepare_flush);
+	dm_init_md_queue(md);
 
 	md->disk = alloc_disk(1);
 	if (!md->disk)
@@ -2161,6 +2160,48 @@ unsigned dm_get_md_type(struct mapped_de
 	return md->type;
 }
 
+/*
+ * Fully initialize a request-based queue (->elevator, ->request_fn, etc).
+ */
+static int dm_init_request_based_queue(struct mapped_device *md)
+{
+	struct request_queue *q = NULL;
+
+	BUG_ON(md->queue->elevator);
+
+	/* Fully initialize the queue */
+	q = blk_init_allocated_queue(md->queue, dm_request_fn, NULL);
+	if (!q)
+		return 0;
+
+	md->queue = q;
+	md->saved_make_request_fn = md->queue->make_request_fn;
+	dm_init_md_queue(md);
+	blk_queue_softirq_done(md->queue, dm_softirq_done);
+	blk_queue_prep_rq(md->queue, dm_prep_fn);
+	blk_queue_lld_busy(md->queue, dm_lld_busy);
+	blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH,
+			  dm_rq_prepare_flush);
+
+	elv_register_queue(md->queue);
+
+	return 1;
+}
+
+/*
+ * Setup the DM device's queue based on md's type
+ */
+int dm_setup_md_queue(struct mapped_device *md)
+{
+	if ((dm_get_md_type(md) == DM_TYPE_REQUEST_BASED) &&
+	    !dm_init_request_based_queue(md)) {
+		DMWARN("Cannot initialize queue for Request-based dm");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static struct mapped_device *dm_find_md(dev_t dev)
 {
 	struct mapped_device *md;
Index: linux-2.6/drivers/md/dm.h
===================================================================
--- linux-2.6.orig/drivers/md/dm.h
+++ linux-2.6/drivers/md/dm.h
@@ -71,6 +71,8 @@ void dm_unlock_md_type(struct mapped_dev
 void dm_set_md_type(struct mapped_device *md, struct dm_table* t);
 unsigned dm_get_md_type(struct mapped_device *md);
 
+int dm_setup_md_queue(struct mapped_device *md);
+
 /*
  * To check the return value from dm_table_find_target().
  */

Re: [PATCH v3 2/2 "v10"] dm: only initialize full request_queue for request-based device

[Kiyoshi Ueda]

Hi Mike,

I ack this patch given that you'll tackle the queue initialization
failure issue afterwards.  I don't see any other problems on this patch.

Acked-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>

Thanks,
Kiyoshi Ueda

On 05/25/2010 11:43 PM +0900, Mike Snitzer wrote:
> Allocate a minimalist request_queue structure initially (needed for both
> bio and request-based DM).  A bio-based DM device no longer defaults to
> having a fully initialized request_queue (request_fn, elevator, etc).
> So bio-based DM devices no longer register elevator sysfs attributes
> ('iosched/' tree or 'scheduler' other than "none").
> 
> Initialization of a full request_queue (request_fn, elevator, etc) is
> deferred until it is known that the DM device is request-based -- at the
> end of the table load sequence.
> 
> Factor DM device's request_queue initialization:
> - common to both request-based and bio-based into dm_init_md_queue().
> - specific to request-based into dm_init_request_based_queue().
> 
> md->type_lock is also used to protect md->queue during table_load().
> md->queue is setup without concern for:
> - another table_load() racing to setup conflicting queue state.
> - do_resume() making a conflicting table live.
> 
> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> ---
>  drivers/md/dm-ioctl.c |   11 +++++
>  drivers/md/dm.c       |   93 ++++++++++++++++++++++++++++++++++++--------------
>  drivers/md/dm.h       |    2 +
>  3 files changed, 79 insertions(+), 27 deletions(-)
> 
> Index: linux-2.6/drivers/md/dm-ioctl.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-ioctl.c
> +++ linux-2.6/drivers/md/dm-ioctl.c
> @@ -1176,11 +1176,20 @@ static int table_load(struct dm_ioctl *p
>  		goto out;
>  	}
>  
> -	/* Protect md->type against concurrent table loads. */
> +	/* Protect md->type and md->queue against concurrent table loads. */
>  	dm_lock_md_type(md);
>  	if (dm_get_md_type(md) == DM_TYPE_NONE) {
>  		/* initial table load, set md's type based on table's type */
>  		dm_set_md_type(md, t);
> +
> +		/* setup md->queue to reflect md's type (may block) */
> +		r = dm_setup_md_queue(md);
> +		if (r) {
> +			DMWARN("unable to setup device queue for this table.");
> +			dm_table_destroy(t);
> +			dm_unlock_md_type(md);
> +			goto out;
> +		}
>  	} else if (dm_get_md_type(md) != dm_table_get_type(t)) {
>  		DMWARN("can't change device type after initial table load.");
>  		dm_table_destroy(t);
> Index: linux-2.6/drivers/md/dm.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm.c
> +++ linux-2.6/drivers/md/dm.c
> @@ -124,7 +124,7 @@ struct mapped_device {
>  
>  	struct request_queue *queue;
>  	unsigned type;
> -	/* Protect type against concurrent access. */
> +	/* Protect queue and type against concurrent access. */
>  	struct mutex type_lock;
>  
>  	struct gendisk *disk;
> @@ -1853,6 +1853,28 @@ static const struct block_device_operati
>  static void dm_wq_work(struct work_struct *work);
>  static void dm_rq_barrier_work(struct work_struct *work);
>  
> +static void dm_init_md_queue(struct mapped_device *md)
> +{
> +	/*
> +	 * 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.
> +	 * The type is decided at the first table loading time.
> +	 * To prevent problematic device stacking, clear the queue flag
> +	 * for request stacking support until then.
> +	 *
> +	 * This queue is new, so no concurrency on the queue_flags.
> +	 */
> +	queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
> +
> +	md->queue->queuedata = md;
> +	md->queue->backing_dev_info.congested_fn = dm_any_congested;
> +	md->queue->backing_dev_info.congested_data = md;
> +	blk_queue_make_request(md->queue, dm_request);
> +	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
> +	md->queue->unplug_fn = dm_unplug_all;
> +	blk_queue_merge_bvec(md->queue, dm_merge_bvec);
> +}
> +
>  /*
>   * Allocate and initialise a blank device with a given minor.
>   */
> @@ -1892,34 +1914,11 @@ static struct mapped_device *alloc_dev(i
>  	INIT_LIST_HEAD(&md->uevent_list);
>  	spin_lock_init(&md->uevent_lock);
>  
> -	md->queue = blk_init_queue(dm_request_fn, NULL);
> +	md->queue = blk_alloc_queue(GFP_KERNEL);
>  	if (!md->queue)
>  		goto bad_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,
> -	 * although we initialized the queue using blk_init_queue().
> -	 * The type is decided at the first table loading time.
> -	 * To prevent problematic device stacking, clear the queue flag
> -	 * for request stacking support until then.
> -	 *
> -	 * This queue is new, so no concurrency on the queue_flags.
> -	 */
> -	queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
> -	md->saved_make_request_fn = md->queue->make_request_fn;
> -	md->queue->queuedata = md;
> -	md->queue->backing_dev_info.congested_fn = dm_any_congested;
> -	md->queue->backing_dev_info.congested_data = md;
> -	blk_queue_make_request(md->queue, dm_request);
> -	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
> -	md->queue->unplug_fn = dm_unplug_all;
> -	blk_queue_merge_bvec(md->queue, dm_merge_bvec);
> -	blk_queue_softirq_done(md->queue, dm_softirq_done);
> -	blk_queue_prep_rq(md->queue, dm_prep_fn);
> -	blk_queue_lld_busy(md->queue, dm_lld_busy);
> -	blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH,
> -			  dm_rq_prepare_flush);
> +	dm_init_md_queue(md);
>  
>  	md->disk = alloc_disk(1);
>  	if (!md->disk)
> @@ -2161,6 +2160,48 @@ unsigned dm_get_md_type(struct mapped_de
>  	return md->type;
>  }
>  
> +/*
> + * Fully initialize a request-based queue (->elevator, ->request_fn, etc).
> + */
> +static int dm_init_request_based_queue(struct mapped_device *md)
> +{
> +	struct request_queue *q = NULL;
> +
> +	BUG_ON(md->queue->elevator);
> +
> +	/* Fully initialize the queue */
> +	q = blk_init_allocated_queue(md->queue, dm_request_fn, NULL);
> +	if (!q)
> +		return 0;
> +
> +	md->queue = q;
> +	md->saved_make_request_fn = md->queue->make_request_fn;
> +	dm_init_md_queue(md);
> +	blk_queue_softirq_done(md->queue, dm_softirq_done);
> +	blk_queue_prep_rq(md->queue, dm_prep_fn);
> +	blk_queue_lld_busy(md->queue, dm_lld_busy);
> +	blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH,
> +			  dm_rq_prepare_flush);
> +
> +	elv_register_queue(md->queue);
> +
> +	return 1;
> +}
> +
> +/*
> + * Setup the DM device's queue based on md's type
> + */
> +int dm_setup_md_queue(struct mapped_device *md)
> +{
> +	if ((dm_get_md_type(md) == DM_TYPE_REQUEST_BASED) &&
> +	    !dm_init_request_based_queue(md)) {
> +		DMWARN("Cannot initialize queue for Request-based dm");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static struct mapped_device *dm_find_md(dev_t dev)
>  {
>  	struct mapped_device *md;
> Index: linux-2.6/drivers/md/dm.h
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm.h
> +++ linux-2.6/drivers/md/dm.h
> @@ -71,6 +71,8 @@ void dm_unlock_md_type(struct mapped_dev
>  void dm_set_md_type(struct mapped_device *md, struct dm_table* t);
>  unsigned dm_get_md_type(struct mapped_device *md);
>  
> +int dm_setup_md_queue(struct mapped_device *md);
> +
>  /*
>   * To check the return value from dm_table_find_target().
>   */