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         holder = bd_find_holder_disk(bdev, disk);
  83         if (holder) {
  84                 holder->refcnt++;
  85                 goto out_unlock;
  86         }
  87
  88         holder = kzalloc(sizeof(*holder), GFP_KERNEL);
  89         if (!holder) {
  90                 ret = -ENOMEM;
  91                 goto out_unlock;
  92         }
  93
  94         INIT_LIST_HEAD(&holder->list);
  95         holder->bdev = bdev;
  96         holder->refcnt = 1;
  97         if (disk->slave_dir) {
  98                 ret = __link_disk_holder(bdev, disk);
  99                 if (ret) {
 100                         kfree(holder);
 101                         goto out_unlock;
 102                 }
 103         }
 104
 105         list_add(&holder->list, &disk->slave_bdevs);
 106         /*
 107          * del_gendisk drops the initial reference to bd_holder_dir, so we need
 108          * to keep our own here to allow for cleanup past that point.
 109          */
 110         kobject_get(bdev->bd_holder_dir);
 111
 112 out_unlock:
 113         mutex_unlock(&disk->open_mutex);
 114         return ret;
 115 }
 116 EXPORT_SYMBOL_GPL(bd_link_disk_holder);
 117
 118 static void __unlink_disk_holder(struct block_device *bdev,
 119                 struct gendisk *disk)
 120 {
 121         del_symlink(disk->slave_dir, bdev_kobj(bdev));
 122         del_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
 123 }
 124
 125 /**
 126  * bd_unlink_disk_holder - destroy symlinks created by bd_link_disk_holder()
 127  * @bdev: the calimed slave bdev
 128  * @disk: the holding disk
 129  *
 130  * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
 131  *
 132  * CONTEXT:
 133  * Might sleep.
 134  */
 135 void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
 136 {
 137         struct bd_holder_disk *holder;
 138
 139         mutex_lock(&disk->open_mutex);
 140         holder = bd_find_holder_disk(bdev, disk);
 141         if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
 142                 if (disk->slave_dir)
 143                         __unlink_disk_holder(bdev, disk);
 144                 kobject_put(bdev->bd_holder_dir);
 145                 list_del_init(&holder->list);
 146                 kfree(holder);
 147         }
 148         mutex_unlock(&disk->open_mutex);
 149 }
 150 EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
 151
 152 int bd_register_pending_holders(struct gendisk *disk)
 153 {
 154         struct bd_holder_disk *holder;
 155         int ret;
 156
 157         mutex_lock(&disk->open_mutex);
 158         list_for_each_entry(holder, &disk->slave_bdevs, list) {
 159                 ret = __link_disk_holder(holder->bdev, disk);
 160                 if (ret)
 161                         goto out_undo;
 162         }
 163         mutex_unlock(&disk->open_mutex);
 164         return 0;
 165
 166 out_undo:
 167         list_for_each_entry_continue_reverse(holder, &disk->slave_bdevs, list)
 168                 __unlink_disk_holder(holder->bdev, disk);
 169         mutex_unlock(&disk->open_mutex);
 170         return ret;
 171 }