xref: /linux/block/holder.c (revision aec499c75cf8e0b599be4d559e6922b613085f8f)
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 
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 
22 static int add_symlink(struct kobject *from, struct kobject *to)
23 {
24 	return sysfs_create_link(from, to, kobject_name(to));
25 }
26 
27 static void del_symlink(struct kobject *from, struct kobject *to)
28 {
29 	sysfs_remove_link(from, kobject_name(to));
30 }
31 
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  */
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 
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  */
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 
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