btrfs-progs: tune: rework the main idea of csum change

adam900710 · kdave · commit 2467f43c29c5 · 2023-05-22T13:11:45.000+02:00
The existing attempt for changing csum types is as the following:

- Create a new temporary csum root
- Generate new data csums into the temporary csum root
- Drop the old csum tree and make the temporary one as csum root
- Change the checksums for metadata in-place

Unfortunately after some experiments, the csum root switch method has a
big pitfall, the backref items in extent tree.

Those backref items still point back to the old tree, meaning without a
lot of extra tricks, the extent tree would be corrupted.

Thus we have to go a new single tree variant:

- Generate new data csums into the csum root
  The new data csums would have a different objectid to distinguish
  them.
- Drop the old data csum items
- Change the key objectids of the new csums
- Change the checksums for metadata in-place

This means unfortunately we have to revert most of the old code, and
update the temporary item format.

The new temporary item would only record the target csum type.
At every stage we have a method to determine the progress, thus no need
for an item, but in the future it's still open for change.

Signed-off-by: Qu Wenruo &lt;wqu@suse.com&gt;
Signed-off-by: David Sterba &lt;dsterba@suse.com&gt;
diff --git a/kernel-shared/ctree.c b/kernel-shared/ctree.c
@@ -403,9 +403,6 @@ int btrfs_create_root(struct btrfs_trans_handle *trans,
 		fs_info->block_group_root = new_root;
 		break;
 
-	case BTRFS_CSUM_TREE_TMP_OBJECTID:
-		fs_info->csum_tree_tmp = new_root;
-		break;
 	/*
 	 * Essential trees can't be created by this function, yet.
 	 * As we expect such skeleton exists, or a lot of functions like
diff --git a/kernel-shared/ctree.h b/kernel-shared/ctree.h
@@ -56,9 +56,8 @@ static inline unsigned long btrfs_chunk_item_size(int num_stripes)
 		sizeof(struct btrfs_stripe) * (num_stripes - 1);
 }
 
-/* Temporary flag not on-disk for blocks that have changed csum already */
-#define BTRFS_HEADER_FLAG_CSUM_NEW		(1ULL << 16)
-#define BTRFS_SUPER_FLAG_CHANGING_CSUM		(1ULL << 37)
+#define BTRFS_SUPER_FLAG_CHANGING_DATA_CSUM	(1ULL << 36)
+#define BTRFS_SUPER_FLAG_CHANGING_META_CSUM	(1ULL << 37)
 
 /*
  * The fs is undergoing block group tree feature change.
@@ -306,9 +305,6 @@ struct btrfs_fs_info {
 	/* the log root tree is a directory of all the other log roots */
 	struct btrfs_root *log_root_tree;
 
-	/* When switching csums */
-	struct btrfs_root *csum_tree_tmp;
-
 	struct cache_tree extent_cache;
 	u64 max_cache_size;
 	u64 cache_size;
@@ -365,7 +361,6 @@ struct btrfs_fs_info {
 	unsigned int skip_leaf_item_checks:1;
 
 	int transaction_aborted;
-	int force_csum_type;
 
 	int (*free_extent_hook)(u64 bytenr, u64 num_bytes, u64 parent,
 				u64 root_objectid, u64 owner, u64 offset,
@@ -670,17 +665,11 @@ static inline u32 BTRFS_MAX_XATTR_SIZE(const struct btrfs_fs_info *info)
  * - balance status item (objectid -4)
  *   (BTRFS_BALANCE_OBJECTID, BTRFS_TEMPORARY_ITEM_KEY, 0)
  *
- * - second csum tree for conversion (objecitd
+ * - second csum tree for conversion (objecitd -13)
+ *   (BTRFS_CSUM_CHANGE_OBJECTID, BTRFS_TEMPORARY_ITEM_KEY, <target csum type>)
  */
 #define BTRFS_TEMPORARY_ITEM_KEY	248
 
-/*
- * Temporary value
- *
- * root tree pointer of checksum tree with new checksum type
- */
-#define BTRFS_CSUM_TREE_TMP_OBJECTID	13ULL
-
 /*
  * Obsolete name, see BTRFS_PERSISTENT_ITEM_KEY
  */
diff --git a/kernel-shared/disk-io.c b/kernel-shared/disk-io.c
@@ -215,12 +215,6 @@ static int csum_tree_block(struct btrfs_fs_info *fs_info,
 	u16 csum_size = fs_info->csum_size;
 	u16 csum_type = fs_info->csum_type;
 
-	if (fs_info->force_csum_type != -1) {
-		/* printf("CSUM TREE: offset %llu\n", buf->start); */
-		csum_type = fs_info->force_csum_type;
-		csum_size = btrfs_csum_type_size(csum_type);
-	}
-
 	if (verify && fs_info->suppress_check_block_errors)
 		return verify_tree_block_csum_silent(buf, csum_size, csum_type);
 	return csum_tree_block_size(buf, csum_size, verify, csum_type);
@@ -475,7 +469,6 @@ int write_tree_block(struct btrfs_trans_handle *trans,
 	if (trans && !btrfs_buffer_uptodate(eb, trans->transid, 0))
 		BUG();
 
-	btrfs_clear_header_flag(eb, BTRFS_HEADER_FLAG_CSUM_NEW);
 	btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
 	csum_tree_block(fs_info, eb, 0);
 
@@ -885,7 +878,6 @@ struct btrfs_fs_info *btrfs_new_fs_info(int writable, u64 sb_bytenr)
 	fs_info->metadata_alloc_profile = (u64)-1;
 	fs_info->system_alloc_profile = fs_info->metadata_alloc_profile;
 	fs_info->nr_global_roots = 1;
-	fs_info->force_csum_type = -1;
 
 	return fs_info;
 
diff --git a/kernel-shared/file-item.c b/kernel-shared/file-item.c
@@ -142,7 +142,6 @@ btrfs_lookup_csum(struct btrfs_trans_handle *trans,
 	struct btrfs_csum_item *item;
 	struct extent_buffer *leaf;
 	u64 csum_offset = 0;
-	u16 csum_type = root->fs_info->csum_type;
 	u16 csum_size = root->fs_info->csum_size;
 	int csums_in_item;
 
@@ -154,11 +153,6 @@ btrfs_lookup_csum(struct btrfs_trans_handle *trans,
 		goto fail;
 	leaf = path->nodes[0];
 
-	if (leaf->fs_info->force_csum_type != -1) {
-		csum_type = root->fs_info->force_csum_type;
-		csum_size = btrfs_csum_type_size(csum_type);
-	}
-
 	if (ret > 0) {
 		ret = 1;
 		if (path->slots[0] == 0)
@@ -208,12 +202,6 @@ int btrfs_csum_file_block(struct btrfs_trans_handle *trans,
 	u16 csum_size = root->fs_info->csum_size;
 	u16 csum_type = root->fs_info->csum_type;
 
-	if (root->fs_info->force_csum_type != -1) {
-		/* printf("CSUM DATA: offset %llu (%d -> %d)\n", bytenr, csum_type, root->fs_info->force_csum_type); */
-		csum_type = root->fs_info->force_csum_type;
-		csum_size = btrfs_csum_type_size(csum_type);
-	}
-
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
diff --git a/kernel-shared/print-tree.c b/kernel-shared/print-tree.c
@@ -790,6 +790,9 @@ void print_objectid(FILE *stream, u64 objectid, u8 type)
 	case BTRFS_BLOCK_GROUP_TREE_OBJECTID:
 		fprintf(stream, "BLOCK_GROUP_TREE");
 		break;
+	case BTRFS_CSUM_CHANGE_OBJECTID:
+		fprintf(stream, "CSUM_CHANGE");
+		break;
 	case (u64)-1:
 		fprintf(stream, "-1");
 		break;
@@ -1142,8 +1145,12 @@ static void print_temporary_item(struct extent_buffer *eb, void *ptr,
 	case BTRFS_BALANCE_OBJECTID:
 		print_balance_item(eb, ptr);
 		break;
-	case BTRFS_CSUM_TREE_TMP_OBJECTID:
-		printf("\t\tcsum tree tmp root %llu\n", offset);
+	case BTRFS_CSUM_CHANGE_OBJECTID:
+		if (offset < btrfs_get_num_csums())
+			printf("\t\ttarget csum type %s (%llu)\n",
+			       btrfs_super_csum_name(offset) ,offset);
+		else
+			printf("\t\tunknown csum type %llu\n", offset);
 		break;
 	default:
 		printf("\t\tunknown temporary item objectid %llu\n", objectid);
diff --git a/kernel-shared/uapi/btrfs_tree.h b/kernel-shared/uapi/btrfs_tree.h
@@ -106,6 +106,7 @@
  */
 #define BTRFS_FREE_INO_OBJECTID -12ULL
 
+#define BTRFS_CSUM_CHANGE_OBJECTID -13ULL
 /* dummy objectid represents multiple objectids */
 #define BTRFS_MULTIPLE_OBJECTIDS -255ULL
 
diff --git a/tune/change-csum.c b/tune/change-csum.c
diff --git a/tune/main.c b/tune/main.c
diff --git a/tune/tune.h b/tune/tune.h
