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Linux/block/holder.c

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  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 

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