1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/genhd.h>
3 #include <linux/slab.h>
4
5 struct bd_holder_disk {
6 struct list_head list;
7 struct block_device *bdev;
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->bdev == bdev)
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
__link_disk_holder(struct block_device * bdev,struct gendisk * disk)32 static int __link_disk_holder(struct block_device *bdev, struct gendisk *disk)
33 {
34 int ret;
35
36 ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
37 if (ret)
38 return ret;
39 ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
40 if (ret)
41 del_symlink(disk->slave_dir, bdev_kobj(bdev));
42 return ret;
43 }
44
45 /**
46 * bd_link_disk_holder - create symlinks between holding disk and slave bdev
47 * @bdev: the claimed slave bdev
48 * @disk: the holding disk
49 *
50 * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
51 *
52 * This functions creates the following sysfs symlinks.
53 *
54 * - from "slaves" directory of the holder @disk to the claimed @bdev
55 * - from "holders" directory of the @bdev to the holder @disk
56 *
57 * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is
58 * passed to bd_link_disk_holder(), then:
59 *
60 * /sys/block/dm-0/slaves/sda --> /sys/block/sda
61 * /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
62 *
63 * The caller must have claimed @bdev before calling this function and
64 * ensure that both @bdev and @disk are valid during the creation and
65 * lifetime of these symlinks.
66 *
67 * CONTEXT:
68 * Might sleep.
69 *
70 * RETURNS:
71 * 0 on success, -errno on failure.
72 */
bd_link_disk_holder(struct block_device * bdev,struct gendisk * disk)73 int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
74 {
75 struct bd_holder_disk *holder;
76 int ret = 0;
77
78 mutex_lock(&disk->open_mutex);
79
80 WARN_ON_ONCE(!bdev->bd_holder);
81
82 /* FIXME: remove the following once add_disk() handles errors */
83 if (WARN_ON(!bdev->bd_holder_dir))
84 goto out_unlock;
85
86 holder = bd_find_holder_disk(bdev, disk);
87 if (holder) {
88 holder->refcnt++;
89 goto out_unlock;
90 }
91
92 holder = kzalloc(sizeof(*holder), GFP_KERNEL);
93 if (!holder) {
94 ret = -ENOMEM;
95 goto out_unlock;
96 }
97
98 INIT_LIST_HEAD(&holder->list);
99 holder->bdev = bdev;
100 holder->refcnt = 1;
101 if (disk->slave_dir) {
102 ret = __link_disk_holder(bdev, disk);
103 if (ret) {
104 kfree(holder);
105 goto out_unlock;
106 }
107 }
108
109 list_add(&holder->list, &disk->slave_bdevs);
110 /*
111 * del_gendisk drops the initial reference to bd_holder_dir, so we need
112 * to keep our own here to allow for cleanup past that point.
113 */
114 kobject_get(bdev->bd_holder_dir);
115
116 out_unlock:
117 mutex_unlock(&disk->open_mutex);
118 return ret;
119 }
120 EXPORT_SYMBOL_GPL(bd_link_disk_holder);
121
__unlink_disk_holder(struct block_device * bdev,struct gendisk * disk)122 static void __unlink_disk_holder(struct block_device *bdev,
123 struct gendisk *disk)
124 {
125 del_symlink(disk->slave_dir, bdev_kobj(bdev));
126 del_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
127 }
128
129 /**
130 * bd_unlink_disk_holder - destroy symlinks created by bd_link_disk_holder()
131 * @bdev: the calimed slave bdev
132 * @disk: the holding disk
133 *
134 * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
135 *
136 * CONTEXT:
137 * Might sleep.
138 */
bd_unlink_disk_holder(struct block_device * bdev,struct gendisk * disk)139 void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
140 {
141 struct bd_holder_disk *holder;
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 if (disk->slave_dir)
147 __unlink_disk_holder(bdev, disk);
148 kobject_put(bdev->bd_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
bd_register_pending_holders(struct gendisk * disk)156 int bd_register_pending_holders(struct gendisk *disk)
157 {
158 struct bd_holder_disk *holder;
159 int ret;
160
161 mutex_lock(&disk->open_mutex);
162 list_for_each_entry(holder, &disk->slave_bdevs, list) {
163 ret = __link_disk_holder(holder->bdev, disk);
164 if (ret)
165 goto out_undo;
166 }
167 mutex_unlock(&disk->open_mutex);
168 return 0;
169
170 out_undo:
171 list_for_each_entry_continue_reverse(holder, &disk->slave_bdevs, list)
172 __unlink_disk_holder(holder->bdev, disk);
173 mutex_unlock(&disk->open_mutex);
174 return ret;
175 }
176