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