// SPDX-License-Identifier: GPL-2.0-only
#include <linux/blkdev.h>
#include <linux/slab.h>

struct bd_holder_disk {
        struct list_head        list;
        struct kobject          *holder_dir;
        int                     refcnt;
};

static DEFINE_MUTEX(blk_holder_mutex);

static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
                                                  struct gendisk *disk)
{
        struct bd_holder_disk *holder;

        list_for_each_entry(holder, &disk->slave_bdevs, list)
                if (holder->holder_dir == bdev->bd_holder_dir)
                        return holder;
        return NULL;
}

static int add_symlink(struct kobject *from, struct kobject *to)
{
        return sysfs_create_link(from, to, kobject_name(to));
}

static void del_symlink(struct kobject *from, struct kobject *to)
{
        sysfs_remove_link(from, kobject_name(to));
}

/**
 * bd_link_disk_holder - create symlinks between holding disk and slave bdev
 * @bdev: the claimed slave bdev
 * @disk: the holding disk
 *
 * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
 *
 * This functions creates the following sysfs symlinks.
 *
 * - from "slaves" directory of the holder @disk to the claimed @bdev
 * - from "holders" directory of the @bdev to the holder @disk
 *
 * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is
 * passed to bd_link_disk_holder(), then:
 *
 *   /sys/block/dm-0/slaves/sda --> /sys/block/sda
 *   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
 *
 * The caller must have claimed @bdev before calling this function and
 * ensure that both @bdev and @disk are valid during the creation and
 * lifetime of these symlinks.
 *
 * CONTEXT:
 * Might sleep.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
{
        struct bd_holder_disk *holder;
        int ret = 0;

        if (WARN_ON_ONCE(!disk->slave_dir))
                return -EINVAL;

        if (bdev->bd_disk == disk)
                return -EINVAL;

        /*
         * del_gendisk drops the initial reference to bd_holder_dir, so we
         * need to keep our own here to allow for cleanup past that point.
         */
        mutex_lock(&bdev->bd_disk->open_mutex);
        if (!disk_live(bdev->bd_disk)) {
                mutex_unlock(&bdev->bd_disk->open_mutex);
                return -ENODEV;
        }
        kobject_get(bdev->bd_holder_dir);
        mutex_unlock(&bdev->bd_disk->open_mutex);

        mutex_lock(&blk_holder_mutex);
        WARN_ON_ONCE(!bdev->bd_holder);

        holder = bd_find_holder_disk(bdev, disk);
        if (holder) {
                kobject_put(bdev->bd_holder_dir);
                holder->refcnt++;
                goto out_unlock;
        }

        holder = kzalloc_obj(*holder);
        if (!holder) {
                ret = -ENOMEM;
                goto out_unlock;
        }

        INIT_LIST_HEAD(&holder->list);
        holder->refcnt = 1;
        holder->holder_dir = bdev->bd_holder_dir;

        ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
        if (ret)
                goto out_free_holder;
        ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
        if (ret)
                goto out_del_symlink;
        list_add(&holder->list, &disk->slave_bdevs);

        mutex_unlock(&blk_holder_mutex);
        return 0;

out_del_symlink:
        del_symlink(disk->slave_dir, bdev_kobj(bdev));
out_free_holder:
        kfree(holder);
out_unlock:
        mutex_unlock(&blk_holder_mutex);
        if (ret)
                kobject_put(bdev->bd_holder_dir);
        return ret;
}
EXPORT_SYMBOL_GPL(bd_link_disk_holder);

/**
 * bd_unlink_disk_holder - destroy symlinks created by bd_link_disk_holder()
 * @bdev: the calimed slave bdev
 * @disk: the holding disk
 *
 * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
 *
 * CONTEXT:
 * Might sleep.
 */
void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
{
        struct bd_holder_disk *holder;

        if (WARN_ON_ONCE(!disk->slave_dir))
                return;

        mutex_lock(&blk_holder_mutex);
        holder = bd_find_holder_disk(bdev, disk);
        if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
                del_symlink(disk->slave_dir, bdev_kobj(bdev));
                del_symlink(holder->holder_dir, &disk_to_dev(disk)->kobj);
                kobject_put(holder->holder_dir);
                list_del_init(&holder->list);
                kfree(holder);
        }
        mutex_unlock(&blk_holder_mutex);
}
EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);