block/holder.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/genhd.h>
   3
   4 struct bd_holder_disk {
   5         struct list_head        list;
   6         struct block_device     *bdev;
   7         int                     refcnt;
   8 };
   9
  10 static 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
  21 static int add_symlink(struct kobject *from, struct kobject *to)
  22 {
  23         return sysfs_create_link(from, to, kobject_name(to));
  24 }
  25
  26 static void del_symlink(struct kobject *from, struct kobject *to)
  27 {
  28         sysfs_remove_link(from, kobject_name(to));
  29 }
  30
  31 static 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  */
  72 int 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
 115 out_unlock:
 116         mutex_unlock(&disk->open_mutex);
 117         return ret;
 118 }
 119 EXPORT_SYMBOL_GPL(bd_link_disk_holder);
 120
 121 static 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  */
 138 void 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 }
 153 EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
 154
 155 int 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
 169 out_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 }