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Commit e09b457b authored by Tejun Heo's avatar Tejun Heo
Browse files

block: simplify holder symlink handling 



Code to manage symlinks in /sys/block/*/{holders|slaves} are overly
complex with multiple holder considerations, redundant extra
references to all involved kobjects, unused generic kobject holder
support and unnecessary mixup with bd_claim/release functionalities.

Strip it down to what's necessary (single gendisk holder) and make it
use a separate interface.  This is a step for cleaning up
bd_claim/release.  This patch makes dm-table slightly more complex but
it will be simplified again with further changes.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarNeil Brown <neilb@suse.de>
Acked-by: default avatarMike Snitzer <snitzer@redhat.com>
Cc: dm-devel@redhat.com
parent 37004c42

drivers/md/dm-table.c

+17 −6
Original line number Diff line number Diff line
@@ -328,14 +328,24 @@ static int open_dev(struct dm_dev_internal *d, dev_t dev, 
	bdev = open_by_devnum(dev, d->dm_dev.mode);

	if (IS_ERR(bdev))

		return PTR_ERR(bdev);

	r = bd_claim_by_disk(bdev, _claim_ptr, dm_disk(md));

	if (r)



	r = bd_claim(bdev, _claim_ptr);

	if (r) {

		blkdev_put(bdev, d->dm_dev.mode);

		return r;

	}



	r = bd_link_disk_holder(bdev, dm_disk(md));

	if (r) {

		bd_release(bdev);

		blkdev_put(bdev, d->dm_dev.mode);

	else

		d->dm_dev.bdev = bdev;

		return r;

	}



	d->dm_dev.bdev = bdev;

	return 0;

}



/*

 * Close a device that we've been using.

 */
@@ -344,7 +354,8 @@ static void close_dev(struct dm_dev_internal *d, struct mapped_device *md) 
	if (!d->dm_dev.bdev)

		return;



	bd_release_from_disk(d->dm_dev.bdev, dm_disk(md));

	bd_unlink_disk_holder(d->dm_dev.bdev);

	bd_release(d->dm_dev.bdev);

	blkdev_put(d->dm_dev.bdev, d->dm_dev.mode);

	d->dm_dev.bdev = NULL;

}

drivers/md/md.c

+2 −2
Original line number Diff line number Diff line
@@ -1880,7 +1880,7 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev) 
	rdev->sysfs_state = sysfs_get_dirent_safe(rdev->kobj.sd, "state");



	list_add_rcu(&rdev->same_set, &mddev->disks);

	bd_claim_by_disk(rdev->bdev, rdev->bdev->bd_holder, mddev->gendisk);

	bd_link_disk_holder(rdev->bdev, mddev->gendisk);



	/* May as well allow recovery to be retried once */

	mddev->recovery_disabled = 0;
@@ -1907,7 +1907,7 @@ static void unbind_rdev_from_array(mdk_rdev_t * rdev) 
		MD_BUG();

		return;

	}

	bd_release_from_disk(rdev->bdev, rdev->mddev->gendisk);

	bd_unlink_disk_holder(rdev->bdev);

	list_del_rcu(&rdev->same_set);

	printk(KERN_INFO "md: unbind<%s>\n", bdevname(rdev->bdev,b));

	rdev->mddev = NULL;

fs/block_dev.c

+44 −278
Original line number Diff line number Diff line
@@ -426,9 +426,6 @@ static void init_once(void *foo) 
	mutex_init(&bdev->bd_mutex);

	INIT_LIST_HEAD(&bdev->bd_inodes);

	INIT_LIST_HEAD(&bdev->bd_list);

#ifdef CONFIG_SYSFS

	INIT_LIST_HEAD(&bdev->bd_holder_list);

#endif

	inode_init_once(&ei->vfs_inode);

	/* Initialize mutex for freeze. */

	mutex_init(&bdev->bd_fsfreeze_mutex);
@@ -881,314 +878,83 @@ void bd_release(struct block_device *bdev) 
EXPORT_SYMBOL(bd_release);



#ifdef CONFIG_SYSFS

/*

 * Functions for bd_claim_by_kobject / bd_release_from_kobject

 *

 *     If a kobject is passed to bd_claim_by_kobject()

 *     and the kobject has a parent directory,

 *     following symlinks are created:

 *        o from the kobject to the claimed bdev

 *        o from "holders" directory of the bdev to the parent of the kobject

 *     bd_release_from_kobject() removes these symlinks.

 *

 *     Example:

 *        If /dev/dm-0 maps to /dev/sda, kobject corresponding to

 *        /sys/block/dm-0/slaves is passed to bd_claim_by_kobject(), then:

 *           /sys/block/dm-0/slaves/sda --> /sys/block/sda

 *           /sys/block/sda/holders/dm-0 --> /sys/block/dm-0

 */



static int add_symlink(struct kobject *from, struct kobject *to)

{

	if (!from || !to)

		return 0;

	return sysfs_create_link(from, to, kobject_name(to));

}



static void del_symlink(struct kobject *from, struct kobject *to)

{

	if (!from || !to)

		return;

	sysfs_remove_link(from, kobject_name(to));

}



/*

 * 'struct bd_holder' contains pointers to kobjects symlinked by

 * bd_claim_by_kobject.

 * It's connected to bd_holder_list which is protected by bdev->bd_sem.

 */

struct bd_holder {

	struct list_head list;	/* chain of holders of the bdev */

	int count;		/* references from the holder */

	struct kobject *sdir;	/* holder object, e.g. "/block/dm-0/slaves" */

	struct kobject *hdev;	/* e.g. "/block/dm-0" */

	struct kobject *hdir;	/* e.g. "/block/sda/holders" */

	struct kobject *sdev;	/* e.g. "/block/sda" */

};



/*

 * Get references of related kobjects at once.

 * Returns 1 on success. 0 on failure.

 *

 * Should call bd_holder_release_dirs() after successful use.

 */

static int bd_holder_grab_dirs(struct block_device *bdev,

			struct bd_holder *bo)

{

	if (!bdev || !bo)

		return 0;



	bo->sdir = kobject_get(bo->sdir);

	if (!bo->sdir)

		return 0;



	bo->hdev = kobject_get(bo->sdir->parent);

	if (!bo->hdev)

		goto fail_put_sdir;



	bo->sdev = kobject_get(&part_to_dev(bdev->bd_part)->kobj);

	if (!bo->sdev)

		goto fail_put_hdev;



	bo->hdir = kobject_get(bdev->bd_part->holder_dir);

	if (!bo->hdir)

		goto fail_put_sdev;



	return 1;



fail_put_sdev:

	kobject_put(bo->sdev);

fail_put_hdev:

	kobject_put(bo->hdev);

fail_put_sdir:

	kobject_put(bo->sdir);



	return 0;

}



/* Put references of related kobjects at once. */

static void bd_holder_release_dirs(struct bd_holder *bo)

{

	kobject_put(bo->hdir);

	kobject_put(bo->sdev);

	kobject_put(bo->hdev);

	kobject_put(bo->sdir);

}



static struct bd_holder *alloc_bd_holder(struct kobject *kobj)

{

	struct bd_holder *bo;



	bo = kzalloc(sizeof(*bo), GFP_KERNEL);

	if (!bo)

		return NULL;



	bo->count = 1;

	bo->sdir = kobj;



	return bo;

}



static void free_bd_holder(struct bd_holder *bo)

{

	kfree(bo);

}



/**

 * find_bd_holder - find matching struct bd_holder from the block device

 *

 * @bdev:	struct block device to be searched

 * @bo:		target struct bd_holder

 *

 * Returns matching entry with @bo in @bdev->bd_holder_list.

 * If found, increment the reference count and return the pointer.

 * If not found, returns NULL.

 */

static struct bd_holder *find_bd_holder(struct block_device *bdev,

					struct bd_holder *bo)

{

	struct bd_holder *tmp;



	list_for_each_entry(tmp, &bdev->bd_holder_list, list)

		if (tmp->sdir == bo->sdir) {

			tmp->count++;

			return tmp;

		}



	return NULL;

}



/**

 * add_bd_holder - create sysfs symlinks for bd_claim() relationship

 * bd_link_disk_holder - create symlinks between holding disk and slave bdev

 * @bdev: the claimed slave bdev

 * @disk: the holding disk

 *

 * @bdev:	block device to be bd_claimed

 * @bo:		preallocated and initialized by alloc_bd_holder()

 *

 * Add @bo to @bdev->bd_holder_list, create symlinks.

 *

 * Returns 0 if symlinks are created.

 * Returns -ve if something fails.

 */

static int add_bd_holder(struct block_device *bdev, struct bd_holder *bo)

{

	int err;



	if (!bo)

		return -EINVAL;



	if (!bd_holder_grab_dirs(bdev, bo))

		return -EBUSY;



	err = add_symlink(bo->sdir, bo->sdev);

	if (err)

		return err;



	err = add_symlink(bo->hdir, bo->hdev);

	if (err) {

		del_symlink(bo->sdir, bo->sdev);

		return err;

	}



	list_add_tail(&bo->list, &bdev->bd_holder_list);

	return 0;

}



/**

 * del_bd_holder - delete sysfs symlinks for bd_claim() relationship

 * This functions creates the following sysfs symlinks.

 *

 * @bdev:	block device to be bd_claimed

 * @kobj:	holder's kobject

 * - from "slaves" directory of the holder @disk to the claimed @bdev

 * - from "holders" directory of the @bdev to the holder @disk

 *

 * If there is matching entry with @kobj in @bdev->bd_holder_list

 * and no other bd_claim() from the same kobject,

 * remove the struct bd_holder from the list, delete symlinks for it.

 * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is

 * passed to bd_link_disk_holder(), then:

 *

 * Returns a pointer to the struct bd_holder when it's removed from the list

 * and ready to be freed.

 * Returns NULL if matching claim isn't found or there is other bd_claim()

 * by the same kobject.

 */

static struct bd_holder *del_bd_holder(struct block_device *bdev,

					struct kobject *kobj)

{

	struct bd_holder *bo;



	list_for_each_entry(bo, &bdev->bd_holder_list, list) {

		if (bo->sdir == kobj) {

			bo->count--;

			BUG_ON(bo->count < 0);

			if (!bo->count) {

				list_del(&bo->list);

				del_symlink(bo->sdir, bo->sdev);

				del_symlink(bo->hdir, bo->hdev);

				bd_holder_release_dirs(bo);

				return bo;

			}

			break;

		}

	}



	return NULL;

}



/**

 * bd_claim_by_kobject - bd_claim() with additional kobject signature

 *   /sys/block/dm-0/slaves/sda --> /sys/block/sda

 *   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0

 *

 * @bdev:	block device to be claimed

 * @holder:	holder's signature

 * @kobj:	holder's kobject

 * The caller must have claimed @bdev before calling this function and

 * ensure that both @bdev and @disk are valid during the creation and

 * lifetime of these symlinks.

 *

 * Do bd_claim() and if it succeeds, create sysfs symlinks between

 * the bdev and the holder's kobject.

 * Use bd_release_from_kobject() when relesing the claimed bdev.

 * CONTEXT:

 * Might sleep.

 *

 * Returns 0 on success. (same as bd_claim())

 * Returns errno on failure.

 * RETURNS:

 * 0 on success, -errno on failure.

 */

static int bd_claim_by_kobject(struct block_device *bdev, void *holder,

				struct kobject *kobj)

int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)

{

	int err;

	struct bd_holder *bo, *found;



	if (!kobj)

		return -EINVAL;



	bo = alloc_bd_holder(kobj);

	if (!bo)

		return -ENOMEM;

	int ret = 0;



	mutex_lock(&bdev->bd_mutex);



	err = bd_claim(bdev, holder);

	if (err)

		goto fail;

	WARN_ON_ONCE(!bdev->bd_holder || bdev->bd_holder_disk);



	found = find_bd_holder(bdev, bo);

	if (found)

		goto fail;

	/* FIXME: remove the following once add_disk() handles errors */

	if (WARN_ON(!disk->slave_dir || !bdev->bd_part->holder_dir))

		goto out_unlock;



	err = add_bd_holder(bdev, bo);

	if (err)

		bd_release(bdev);

	else

		bo = NULL;

fail:

	mutex_unlock(&bdev->bd_mutex);

	free_bd_holder(bo);

	return err;

}

	ret = add_symlink(disk->slave_dir, &part_to_dev(bdev->bd_part)->kobj);

	if (ret)

		goto out_unlock;



/**

 * bd_release_from_kobject - bd_release() with additional kobject signature

 *

 * @bdev:	block device to be released

 * @kobj:	holder's kobject

 *

 * Do bd_release() and remove sysfs symlinks created by bd_claim_by_kobject().

 */

static void bd_release_from_kobject(struct block_device *bdev,

					struct kobject *kobj)

{

	if (!kobj)

		return;

	ret = add_symlink(bdev->bd_part->holder_dir, &disk_to_dev(disk)->kobj);

	if (ret) {

		del_symlink(disk->slave_dir, &part_to_dev(bdev->bd_part)->kobj);

		goto out_unlock;

	}



	mutex_lock(&bdev->bd_mutex);

	bd_release(bdev);

	free_bd_holder(del_bd_holder(bdev, kobj));

	bdev->bd_holder_disk = disk;

out_unlock:

	mutex_unlock(&bdev->bd_mutex);

	return ret;

}

EXPORT_SYMBOL_GPL(bd_link_disk_holder);



/**

 * bd_claim_by_disk - wrapper function for bd_claim_by_kobject()

 *

 * @bdev:	block device to be claimed

 * @holder:	holder's signature

 * @disk:	holder's gendisk

 *

 * Call bd_claim_by_kobject() with getting @disk->slave_dir.

 */

int bd_claim_by_disk(struct block_device *bdev, void *holder,

			struct gendisk *disk)

void bd_unlink_disk_holder(struct block_device *bdev)

{

	return bd_claim_by_kobject(bdev, holder, kobject_get(disk->slave_dir));

}

EXPORT_SYMBOL_GPL(bd_claim_by_disk);

	struct gendisk *disk = bdev->bd_holder_disk;



/**

 * bd_release_from_disk - wrapper function for bd_release_from_kobject()

 *

 * @bdev:	block device to be claimed

 * @disk:	holder's gendisk

 *

 * Call bd_release_from_kobject() and put @disk->slave_dir.

 */

void bd_release_from_disk(struct block_device *bdev, struct gendisk *disk)

{

	bd_release_from_kobject(bdev, disk->slave_dir);

	kobject_put(disk->slave_dir);

	bdev->bd_holder_disk = NULL;

	if (!disk)

		return;



	del_symlink(disk->slave_dir, &part_to_dev(bdev->bd_part)->kobj);

	del_symlink(bdev->bd_part->holder_dir, &disk_to_dev(disk)->kobj);

}

EXPORT_SYMBOL_GPL(bd_release_from_disk);

EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);

#endif



/*

include/linux/fs.h

+11 −5
Original line number Diff line number Diff line
@@ -663,7 +663,7 @@ struct block_device { 
	void *			bd_holder;

	int			bd_holders;

#ifdef CONFIG_SYSFS

	struct list_head	bd_holder_list;

	struct gendisk *	bd_holder_disk;	/* for sysfs slave linkng */

#endif

	struct block_device *	bd_contains;

	unsigned		bd_block_size;
@@ -2042,11 +2042,17 @@ extern int blkdev_put(struct block_device *, fmode_t); 
extern int bd_claim(struct block_device *, void *);

extern void bd_release(struct block_device *);

#ifdef CONFIG_SYSFS

extern int bd_claim_by_disk(struct block_device *, void *, struct gendisk *);

extern void bd_release_from_disk(struct block_device *, struct gendisk *);

extern int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk);

extern void bd_unlink_disk_holder(struct block_device *bdev);

#else

#define bd_claim_by_disk(bdev, holder, disk)	bd_claim(bdev, holder)

#define bd_release_from_disk(bdev, disk)	bd_release(bdev)

static inline int bd_link_disk_holder(struct block_device *bdev,

				      struct gendisk *disk)

{

	return 0;

}

static inline void bd_unlink_disk_holder(struct block_device *bdev)

{

}

#endif

#endif