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 kobject          *holder_dir;
   8         int                     refcnt;
   9 };
  10
  11 static DEFINE_MUTEX(blk_holder_mutex);
  12
  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
  24 static int add_symlink(struct kobject *from, struct kobject *to)
  25 {
  26         return sysfs_create_link(from, to, kobject_name(to));
  27 }
  28
  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  */
  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  */
 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);