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 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->holder_dir == bdev->bd_holder_dir)
  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 /**
  33  * bd_link_disk_holder - create symlinks between holding disk and slave bdev
  34  * @bdev: the claimed slave bdev
  35  * @disk: the holding disk
  36  *
  37  * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
  38  *
  39  * This functions creates the following sysfs symlinks.
  40  *
  41  * - from "slaves" directory of the holder @disk to the claimed @bdev
  42  * - from "holders" directory of the @bdev to the holder @disk
  43  *
  44  * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is
  45  * passed to bd_link_disk_holder(), then:
  46  *
  47  *   /sys/block/dm-0/slaves/sda --> /sys/block/sda
  48  *   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
  49  *
  50  * The caller must have claimed @bdev before calling this function and
  51  * ensure that both @bdev and @disk are valid during the creation and
  52  * lifetime of these symlinks.
  53  *
  54  * CONTEXT:
  55  * Might sleep.
  56  *
  57  * RETURNS:
  58  * 0 on success, -errno on failure.
  59  */
  60 int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
  61 {
  62         struct bd_holder_disk *holder;
  63         int ret = 0;
  64
  65         if (WARN_ON_ONCE(!disk->slave_dir))
  66                 return -EINVAL;
  67
  68         if (bdev->bd_disk == disk)
  69                 return -EINVAL;
  70
  71         /*
  72          * del_gendisk drops the initial reference to bd_holder_dir, so we
  73          * need to keep our own here to allow for cleanup past that point.
  74          */
  75         mutex_lock(&bdev->bd_disk->open_mutex);
  76         if (!disk_live(bdev->bd_disk)) {
  77                 mutex_unlock(&bdev->bd_disk->open_mutex);
  78                 return -ENODEV;
  79         }
  80         kobject_get(bdev->bd_holder_dir);
  81         mutex_unlock(&bdev->bd_disk->open_mutex);
  82
  83         mutex_lock(&disk->open_mutex);
  84         WARN_ON_ONCE(!bdev->bd_holder);
  85
  86         holder = bd_find_holder_disk(bdev, disk);
  87         if (holder) {
  88                 kobject_put(bdev->bd_holder_dir);
  89                 holder->refcnt++;
  90                 goto out_unlock;
  91         }
  92
  93         holder = kzalloc(sizeof(*holder), GFP_KERNEL);
  94         if (!holder) {
  95                 ret = -ENOMEM;
  96                 goto out_unlock;
  97         }
  98
  99         INIT_LIST_HEAD(&holder->list);
 100         holder->refcnt = 1;
 101         holder->holder_dir = bdev->bd_holder_dir;
 102
 103         ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
 104         if (ret)
 105                 goto out_free_holder;
 106         ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
 107         if (ret)
 108                 goto out_del_symlink;
 109         list_add(&holder->list, &disk->slave_bdevs);
 110
 111         mutex_unlock(&disk->open_mutex);
 112         return 0;
 113
 114 out_del_symlink:
 115         del_symlink(disk->slave_dir, bdev_kobj(bdev));
 116 out_free_holder:
 117         kfree(holder);
 118 out_unlock:
 119         mutex_unlock(&disk->open_mutex);
 120         if (ret)
 121                 kobject_put(bdev->bd_holder_dir);
 122         return ret;
 123 }
 124 EXPORT_SYMBOL_GPL(bd_link_disk_holder);
 125
 126 /**
 127  * bd_unlink_disk_holder - destroy symlinks created by bd_link_disk_holder()
 128  * @bdev: the calimed slave bdev
 129  * @disk: the holding disk
 130  *
 131  * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
 132  *
 133  * CONTEXT:
 134  * Might sleep.
 135  */
 136 void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
 137 {
 138         struct bd_holder_disk *holder;
 139
 140         if (WARN_ON_ONCE(!disk->slave_dir))
 141                 return;
 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                 del_symlink(disk->slave_dir, bdev_kobj(bdev));
 147                 del_symlink(holder->holder_dir, &disk_to_dev(disk)->kobj);
 148                 kobject_put(holder->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);