[RFC PATCH v14 12/19] dm: add finalize hook to target_type

[Fan Wu <wufan@linux.microsoft.com>]

This patch adds a target finalize hook.

The hook is triggered just before activating an inactive table of a
mapped device. If it returns an error the __bind get cancelled.

The dm-verity target will use this hook to attach the dm-verity's
roothash metadata to the block_device struct of the mapped device.

Signed-off-by: Fan Wu <wufan@linux.microsoft.com>

---
v1-v10:
  + Not present

v11:
  + Introduced

v12:
  + No changes

v13:
  + No changes

v14:
  + Add documentation
---
 drivers/md/dm.c               | 12 ++++++++++++
 include/linux/device-mapper.h |  9 +++++++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8dcabf84d866..15b46edae49f 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2266,6 +2266,18 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
 		goto out;
 	}
 
+	for (unsigned int i = 0; i < t->num_targets; i++) {
+		struct dm_target *ti = dm_table_get_target(t, i);
+
+		if (ti->type->finalize) {
+			ret = ti->type->finalize(ti);
+			if (ret) {
+				old_map = ERR_PTR(ret);
+				goto out;
+			}
+		}
+	}
+
 	old_map = rcu_dereference_protected(md->map, lockdep_is_held(&md->suspend_lock));
 	rcu_assign_pointer(md->map, (void *)t);
 	md->immutable_target_type = dm_table_get_immutable_target_type(t);
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 772ab4d74d94..d7a0ba1fa19e 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -160,6 +160,14 @@ typedef int (*dm_dax_zero_page_range_fn)(struct dm_target *ti, pgoff_t pgoff,
  */
 typedef size_t (*dm_dax_recovery_write_fn)(struct dm_target *ti, pgoff_t pgoff,
 		void *addr, size_t bytes, struct iov_iter *i);
+/*
+ * This hook allows DM targets in an inactive table to complete their setup
+ * before the table is made active.
+ * Returns:
+ *  < 0 : error
+ *  = 0 : success
+ */
+typedef int (*dm_finalize_fn) (struct dm_target *target);
 
 void dm_error(const char *message);
 
@@ -210,6 +218,7 @@ struct target_type {
 	dm_dax_direct_access_fn direct_access;
 	dm_dax_zero_page_range_fn dax_zero_page_range;
 	dm_dax_recovery_write_fn dax_recovery_write;
+	dm_finalize_fn finalize;
 
 	/* For internal device-mapper use. */
 	struct list_head list;
-- 
2.43.1