block/holder.c

   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 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 }