1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/blkdev.h>
3 #include <linux/slab.h>
4
5 struct bd_holder_disk {
6 struct list_head list;
7 struct kobject *holder_dir;
8 int refcnt;
9 };
10
bd_find_holder_disk(struct block_device * bdev,struct gendisk * disk)11 static 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
add_symlink(struct kobject * from,struct kobject * to)22 static int add_symlink(struct kobject *from, struct kobject *to)
23 {
24 return sysfs_create_link(from, to, kobject_name(to));
25 }
26
del_symlink(struct kobject * from,struct kobject * to)27 static 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 */
bd_link_disk_holder(struct block_device * bdev,struct gendisk * disk)60 int 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
114 out_del_symlink:
115 del_symlink(disk->slave_dir, bdev_kobj(bdev));
116 out_free_holder:
117 kfree(holder);
118 out_unlock:
119 mutex_unlock(&disk->open_mutex);
120 if (ret)
121 kobject_put(bdev->bd_holder_dir);
122 return ret;
123 }
124 EXPORT_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 */
bd_unlink_disk_holder(struct block_device * bdev,struct gendisk * disk)136 void 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 }
154 EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
155