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
11 static DEFINE_MUTEX(blk_holder_mutex);
12
13 static 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
24 static int add_symlink(struct kobject *from, struct kobject *to)
25 {
26 return sysfs_create_link(from, to, kobject_name(to));
27 }
28
29 static 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 */
62 int 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
116 out_del_symlink:
117 del_symlink(disk->slave_dir, bdev_kobj(bdev));
118 out_free_holder:
119 kfree(holder);
120 out_unlock:
121 mutex_unlock(&blk_holder_mutex);
122 if (ret)
123 kobject_put(bdev->bd_holder_dir);
124 return ret;
125 }
126 EXPORT_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 */
138 void 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 }
156 EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
157
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