xref: /linux/block/holder.c (revision 79790b6818e96c58fe2bffee1b418c16e64e7b80)
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 
bd_find_holder_disk(struct block_device * bdev,struct gendisk * disk)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 
add_symlink(struct kobject * from,struct kobject * to)24 static int add_symlink(struct kobject *from, struct kobject *to)
25 {
26 	return sysfs_create_link(from, to, kobject_name(to));
27 }
28 
del_symlink(struct kobject * from,struct kobject * to)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  */
bd_link_disk_holder(struct block_device * bdev,struct gendisk * disk)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  */
bd_unlink_disk_holder(struct block_device * bdev,struct gendisk * disk)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