1// SPDX-License-Identifier: GPL-2.0-only
  2#include <linux/blkdev.h>
  3#include <linux/slab.h>
  4
  5struct bd_holder_disk {
  6	struct list_head	list;
  7	struct kobject		*holder_dir;
  8	int			refcnt;
  9};
 10
 11static DEFINE_MUTEX(blk_holder_mutex);
 12
 13static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
 14						  struct gendisk *disk)
 15{
 16	struct bd_holder_disk *holder;
 17
 18	list_for_each_entry(holder, &disk->slave_bdevs, list)
 19		if (holder->holder_dir == bdev->bd_holder_dir)
 20			return holder;
 21	return NULL;
 22}
 23
 24static int add_symlink(struct kobject *from, struct kobject *to)
 25{
 26	return sysfs_create_link(from, to, kobject_name(to));
 27}
 28
 29static void del_symlink(struct kobject *from, struct kobject *to)
 30{
 31	sysfs_remove_link(from, kobject_name(to));
 32}
 33
 34/**
 35 * bd_link_disk_holder - create symlinks between holding disk and slave bdev
 36 * @bdev: the claimed slave bdev
 37 * @disk: the holding disk
 38 *
 39 * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
 40 *
 41 * This functions creates the following sysfs symlinks.
 42 *
 43 * - from "slaves" directory of the holder @disk to the claimed @bdev
 44 * - from "holders" directory of the @bdev to the holder @disk
 45 *
 46 * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is
 47 * passed to bd_link_disk_holder(), then:
 48 *
 49 *   /sys/block/dm-0/slaves/sda --> /sys/block/sda
 50 *   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
 51 *
 52 * The caller must have claimed @bdev before calling this function and
 53 * ensure that both @bdev and @disk are valid during the creation and
 54 * lifetime of these symlinks.
 55 *
 56 * CONTEXT:
 57 * Might sleep.
 58 *
 59 * RETURNS:
 60 * 0 on success, -errno on failure.
 61 */
 62int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 63{
 64	struct bd_holder_disk *holder;
 65	int ret = 0;
 66
 67	if (WARN_ON_ONCE(!disk->slave_dir))
 68		return -EINVAL;
 69
 70	if (bdev->bd_disk == disk)
 71		return -EINVAL;
 72
 73	/*
 74	 * del_gendisk drops the initial reference to bd_holder_dir, so we
 75	 * need to keep our own here to allow for cleanup past that point.
 76	 */
 77	mutex_lock(&bdev->bd_disk->open_mutex);
 78	if (!disk_live(bdev->bd_disk)) {
 79		mutex_unlock(&bdev->bd_disk->open_mutex);
 80		return -ENODEV;
 81	}
 82	kobject_get(bdev->bd_holder_dir);
 83	mutex_unlock(&bdev->bd_disk->open_mutex);
 84
 85	mutex_lock(&blk_holder_mutex);
 86	WARN_ON_ONCE(!bdev->bd_holder);
 87
 88	holder = bd_find_holder_disk(bdev, disk);
 89	if (holder) {
 90		kobject_put(bdev->bd_holder_dir);
 91		holder->refcnt++;
 92		goto out_unlock;
 93	}
 94
 95	holder = kzalloc(sizeof(*holder), GFP_KERNEL);
 96	if (!holder) {
 97		ret = -ENOMEM;
 98		goto out_unlock;
 99	}
100
101	INIT_LIST_HEAD(&holder->list);
102	holder->refcnt = 1;
103	holder->holder_dir = bdev->bd_holder_dir;
104
105	ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
106	if (ret)
107		goto out_free_holder;
108	ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
109	if (ret)
110		goto out_del_symlink;
111	list_add(&holder->list, &disk->slave_bdevs);
112
113	mutex_unlock(&blk_holder_mutex);
114	return 0;
115
116out_del_symlink:
117	del_symlink(disk->slave_dir, bdev_kobj(bdev));
118out_free_holder:
119	kfree(holder);
120out_unlock:
121	mutex_unlock(&blk_holder_mutex);
122	if (ret)
123		kobject_put(bdev->bd_holder_dir);
124	return ret;
125}
126EXPORT_SYMBOL_GPL(bd_link_disk_holder);
127
128/**
129 * bd_unlink_disk_holder - destroy symlinks created by bd_link_disk_holder()
130 * @bdev: the calimed slave bdev
131 * @disk: the holding disk
132 *
133 * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
134 *
135 * CONTEXT:
136 * Might sleep.
137 */
138void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
139{
140	struct bd_holder_disk *holder;
141
142	if (WARN_ON_ONCE(!disk->slave_dir))
143		return;
144
145	mutex_lock(&blk_holder_mutex);
146	holder = bd_find_holder_disk(bdev, disk);
147	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
148		del_symlink(disk->slave_dir, bdev_kobj(bdev));
149		del_symlink(holder->holder_dir, &disk_to_dev(disk)->kobj);
150		kobject_put(holder->holder_dir);
151		list_del_init(&holder->list);
152		kfree(holder);
153	}
154	mutex_unlock(&blk_holder_mutex);
155}
156EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);