LXR linux/block/holder.c

   1// SPDX-License-Identifier: GPL-2.0-only
   2#include <linux/genhd.h>
   3
   4struct bd_holder_disk {
   5        struct list_head        list;
   6        struct block_device     *bdev;
   7        int                     refcnt;
   8};
   9
  10static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
  11                                                  struct gendisk *disk)
  12{
  13        struct bd_holder_disk *holder;
  14
  15        list_for_each_entry(holder, &disk->slave_bdevs, list)
  16                if (holder->bdev == bdev)
  17                        return holder;
  18        return NULL;
  19}
  20
  21static int add_symlink(struct kobject *from, struct kobject *to)
  22{
  23        return sysfs_create_link(from, to, kobject_name(to));
  24}
  25
  26static void del_symlink(struct kobject *from, struct kobject *to)
  27{
  28        sysfs_remove_link(from, kobject_name(to));
  29}
  30
  31static int __link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  32{
  33        int ret;
  34
  35        ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
  36        if (ret)
  37                return ret;
  38        ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
  39        if (ret)
  40                del_symlink(disk->slave_dir, bdev_kobj(bdev));
  41        return ret;
  42}
  43
  44/**
  45 * bd_link_disk_holder - create symlinks between holding disk and slave bdev
  46 * @bdev: the claimed slave bdev
  47 * @disk: the holding disk
  48 *
  49 * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
  50 *
  51 * This functions creates the following sysfs symlinks.
  52 *
  53 * - from "slaves" directory of the holder @disk to the claimed @bdev
  54 * - from "holders" directory of the @bdev to the holder @disk
  55 *
  56 * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is
  57 * passed to bd_link_disk_holder(), then:
  58 *
  59 *   /sys/block/dm-0/slaves/sda --> /sys/block/sda
  60 *   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
  61 *
  62 * The caller must have claimed @bdev before calling this function and
  63 * ensure that both @bdev and @disk are valid during the creation and
  64 * lifetime of these symlinks.
  65 *
  66 * CONTEXT:
  67 * Might sleep.
  68 *
  69 * RETURNS:
  70 * 0 on success, -errno on failure.
  71 */
  72int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  73{
  74        struct bd_holder_disk *holder;
  75        int ret = 0;
  76
  77        mutex_lock(&disk->open_mutex);
  78
  79        WARN_ON_ONCE(!bdev->bd_holder);
  80
  81        /* FIXME: remove the following once add_disk() handles errors */
  82        if (WARN_ON(!bdev->bd_holder_dir))
  83                goto out_unlock;
  84
  85        holder = bd_find_holder_disk(bdev, disk);
  86        if (holder) {
  87                holder->refcnt++;
  88                goto out_unlock;
  89        }
  90
  91        holder = kzalloc(sizeof(*holder), GFP_KERNEL);
  92        if (!holder) {
  93                ret = -ENOMEM;
  94                goto out_unlock;
  95        }
  96
  97        INIT_LIST_HEAD(&holder->list);
  98        holder->bdev = bdev;
  99        holder->refcnt = 1;
 100        if (disk->slave_dir) {
 101                ret = __link_disk_holder(bdev, disk);
 102                if (ret) {
 103                        kfree(holder);
 104                        goto out_unlock;
 105                }
 106        }
 107
 108        list_add(&holder->list, &disk->slave_bdevs);
 109        /*
 110         * del_gendisk drops the initial reference to bd_holder_dir, so we need
 111         * to keep our own here to allow for cleanup past that point.
 112         */
 113        kobject_get(bdev->bd_holder_dir);
 114
 115out_unlock:
 116        mutex_unlock(&disk->open_mutex);
 117        return ret;
 118}
 119EXPORT_SYMBOL_GPL(bd_link_disk_holder);
 120
 121static void __unlink_disk_holder(struct block_device *bdev,
 122                struct gendisk *disk)
 123{
 124        del_symlink(disk->slave_dir, bdev_kobj(bdev));
 125        del_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
 126}
 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 */
 138void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
 139{
 140        struct bd_holder_disk *holder;
 141
 142        mutex_lock(&disk->open_mutex);
 143        holder = bd_find_holder_disk(bdev, disk);
 144        if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
 145                if (disk->slave_dir)
 146                        __unlink_disk_holder(bdev, disk);
 147                kobject_put(bdev->bd_holder_dir);
 148                list_del_init(&holder->list);
 149                kfree(holder);
 150        }
 151        mutex_unlock(&disk->open_mutex);
 152}
 153EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
 154
 155int bd_register_pending_holders(struct gendisk *disk)
 156{
 157        struct bd_holder_disk *holder;
 158        int ret;
 159
 160        mutex_lock(&disk->open_mutex);
 161        list_for_each_entry(holder, &disk->slave_bdevs, list) {
 162                ret = __link_disk_holder(holder->bdev, disk);
 163                if (ret)
 164                        goto out_undo;
 165        }
 166        mutex_unlock(&disk->open_mutex);
 167        return 0;
 168
 169out_undo:
 170        list_for_each_entry_continue_reverse(holder, &disk->slave_bdevs, list)
 171                __unlink_disk_holder(holder->bdev, disk);
 172        mutex_unlock(&disk->open_mutex);
 173        return ret;
 174}
 175