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); 157