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);
157