[PATCH 3.16 065/245] dm thin metadata: Add support for a pre-commit callback

[Ben Hutchings]

3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nikos Tsironis <ntsironis@xxxxxxxxxxx>

commit ecda7c0280e6b3398459dc589b9a41c1adb45529 upstream.

Add support for one pre-commit callback which is run right before the
metadata are committed.

This allows the thin provisioning target to run a callback before the
metadata are committed and is required by the next commit.

Signed-off-by: Nikos Tsironis <ntsironis@xxxxxxxxxxx>
Acked-by: Joe Thornber <ejt@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
[bwh: Backported to 3.16:
 - Open-code pmd_write_{lock_in_core,unlock}()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/md/dm-thin-metadata.c | 29 +++++++++++++++++++++++++++++
 drivers/md/dm-thin-metadata.h |  7 +++++++
 2 files changed, 36 insertions(+)

--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -198,6 +198,15 @@ struct dm_pool_metadata {
 	bool fail_io:1;
 
 	/*
+	 * Pre-commit callback.
+	 *
+	 * This allows the thin provisioning target to run a callback before
+	 * the metadata are committed.
+	 */
+	dm_pool_pre_commit_fn pre_commit_fn;
+	void *pre_commit_context;
+
+	/*
 	 * Reading the space map roots can fail, so we read it into these
 	 * buffers before the superblock is locked and updated.
 	 */
@@ -784,6 +793,14 @@ static int __commit_transaction(struct d
 	 */
 	BUILD_BUG_ON(sizeof(struct thin_disk_superblock) > 512);
 
+	if (pmd->pre_commit_fn) {
+		r = pmd->pre_commit_fn(pmd->pre_commit_context);
+		if (r < 0) {
+			DMERR("pre-commit callback failed");
+			return r;
+		}
+	}
+
 	r = __write_changed_details(pmd);
 	if (r < 0)
 		return r;
@@ -844,6 +861,8 @@ struct dm_pool_metadata *dm_pool_metadat
 	pmd->fail_io = false;
 	pmd->bdev = bdev;
 	pmd->data_block_size = data_block_size;
+	pmd->pre_commit_fn = NULL;
+	pmd->pre_commit_context = NULL;
 
 	r = __create_persistent_data_objects(pmd, format_device);
 	if (r) {
@@ -1789,6 +1808,16 @@ int dm_pool_register_metadata_threshold(
 	return r;
 }
 
+void dm_pool_register_pre_commit_callback(struct dm_pool_metadata *pmd,
+					  dm_pool_pre_commit_fn fn,
+					  void *context)
+{
+	down_write(&pmd->root_lock);
+	pmd->pre_commit_fn = fn;
+	pmd->pre_commit_context = context;
+	up_write(&pmd->root_lock);
+}
+
 int dm_pool_metadata_set_needs_check(struct dm_pool_metadata *pmd)
 {
 	int r;
--- a/drivers/md/dm-thin-metadata.h
+++ b/drivers/md/dm-thin-metadata.h
@@ -213,6 +213,13 @@ int dm_pool_register_metadata_threshold(
 int dm_pool_metadata_set_needs_check(struct dm_pool_metadata *pmd);
 bool dm_pool_metadata_needs_check(struct dm_pool_metadata *pmd);
 
+/* Pre-commit callback */
+typedef int (*dm_pool_pre_commit_fn)(void *context);
+
+void dm_pool_register_pre_commit_callback(struct dm_pool_metadata *pmd,
+					  dm_pool_pre_commit_fn fn,
+					  void *context);
+
 /*----------------------------------------------------------------*/
 
 #endif