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Commit fa70d2e2 authored by Mike Snitzer's avatar Mike Snitzer Committed by Jens Axboe
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block: allow gendisk's request_queue registration to be deferred 



Since I can remember DM has forced the block layer to allow the
allocation and initialization of the request_queue to be distinct
operations.  Reason for this is block/genhd.c:add_disk() has requires
that the request_queue (and associated bdi) be tied to the gendisk
before add_disk() is called -- because add_disk() also deals with
exposing the request_queue via blk_register_queue().

DM's dynamic creation of arbitrary device types (and associated
request_queue types) requires the DM device's gendisk be available so
that DM table loads can establish a master/slave relationship with
subordinate devices that are referenced by loaded DM tables -- using
bd_link_disk_holder().  But until these DM tables, and their associated
subordinate devices, are known DM cannot know what type of request_queue
it needs -- nor what its queue_limits should be.

This chicken and egg scenario has created all manner of problems for DM
and, at times, the block layer.

Summary of changes:

- Add device_add_disk_no_queue_reg() and add_disk_no_queue_reg() variant
  that drivers may use to add a disk without also calling
  blk_register_queue().  Driver must call blk_register_queue() once its
  request_queue is fully initialized.

- Return early from blk_unregister_queue() if QUEUE_FLAG_REGISTERED
  is not set.  It won't be set if driver used add_disk_no_queue_reg()
  but driver encounters an error and must del_gendisk() before calling
  blk_register_queue().

- Export blk_register_queue().

These changes allow DM to use add_disk_no_queue_reg() to anchor its
gendisk as the "master" for master/slave relationships DM must establish
with subordinate devices referenced in DM tables that get loaded.  Once
all "slave" devices for a DM device are known its request_queue can be
properly initialized and then advertised via sysfs -- important
improvement being that no request_queue resource initialization
performed by blk_register_queue() is missed for DM devices anymore.

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 667257e8

block/blk-sysfs.c

+5 −0
Original line number Diff line number Diff line
@@ -921,6 +921,7 @@ int blk_register_queue(struct gendisk *disk) 
	mutex_unlock(&q->sysfs_lock);

	return ret;

}

EXPORT_SYMBOL_GPL(blk_register_queue);



void blk_unregister_queue(struct gendisk *disk)

{
@@ -929,6 +930,10 @@ void blk_unregister_queue(struct gendisk *disk) 
	if (WARN_ON(!q))

		return;



	/* Return early if disk->queue was never registered. */

	if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))

		return;



	/*

	 * Protect against the 'queue' kobj being accessed

	 * while/after it is removed.

block/genhd.c

+17 −3
Original line number Diff line number Diff line
@@ -629,16 +629,18 @@ static void register_disk(struct device *parent, struct gendisk *disk) 
}



/**

 * device_add_disk - add partitioning information to kernel list

 * __device_add_disk - add disk information to kernel list

 * @parent: parent device for the disk

 * @disk: per-device partitioning information

 * @register_queue: register the queue if set to true

 *

 * This function registers the partitioning information in @disk

 * with the kernel.

 *

 * FIXME: error handling

 */

void device_add_disk(struct device *parent, struct gendisk *disk)

static void __device_add_disk(struct device *parent, struct gendisk *disk,

			      bool register_queue)

{

	dev_t devt;

	int retval;
@@ -682,6 +684,7 @@ void device_add_disk(struct device *parent, struct gendisk *disk) 
				    exact_match, exact_lock, disk);

	}

	register_disk(parent, disk);

	if (register_queue)

		blk_register_queue(disk);



	/*
@@ -693,8 +696,19 @@ void device_add_disk(struct device *parent, struct gendisk *disk) 
	disk_add_events(disk);

	blk_integrity_add(disk);

}



void device_add_disk(struct device *parent, struct gendisk *disk)

{

	__device_add_disk(parent, disk, true);

}

EXPORT_SYMBOL(device_add_disk);



void device_add_disk_no_queue_reg(struct device *parent, struct gendisk *disk)

{

	__device_add_disk(parent, disk, false);

}

EXPORT_SYMBOL(device_add_disk_no_queue_reg);



void del_gendisk(struct gendisk *disk)

{

	struct disk_part_iter piter;

include/linux/genhd.h

+5 −0
Original line number Diff line number Diff line
@@ -395,6 +395,11 @@ static inline void add_disk(struct gendisk *disk) 
{

	device_add_disk(NULL, disk);

}

extern void device_add_disk_no_queue_reg(struct device *parent, struct gendisk *disk);

static inline void add_disk_no_queue_reg(struct gendisk *disk)

{

	device_add_disk_no_queue_reg(NULL, disk);

}



extern void del_gendisk(struct gendisk *gp);

extern struct gendisk *get_gendisk(dev_t dev, int *partno);