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-rw-r--r--block/holder.c154
1 files changed, 154 insertions, 0 deletions
diff --git a/block/holder.c b/block/holder.c
new file mode 100644
index 0000000000..37d18c13d9
--- /dev/null
+++ b/block/holder.c
@@ -0,0 +1,154 @@
+// 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 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(&disk->open_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(sizeof(*holder), GFP_KERNEL);
+ 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(&disk->open_mutex);
+ return 0;
+
+out_del_symlink:
+ del_symlink(disk->slave_dir, bdev_kobj(bdev));
+out_free_holder:
+ kfree(holder);
+out_unlock:
+ mutex_unlock(&disk->open_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(&disk->open_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(&disk->open_mutex);
+}
+EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);