Mixed back reference (FORWARD ROLLING FORMAT CHANGE)

This commit introduces a new kind of back reference for btrfs metadata.
Once a filesystem has been mounted with this commit, IT WILL NO LONGER
BE MOUNTABLE BY OLDER KERNELS.

The new back ref provides information about pointer's key, level and in which
tree the pointer lives. This information allow us to find the pointer by
searching the tree. The shortcoming of the new back ref is that it only works
for pointers in tree blocks referenced by their owner trees.

This is mostly a problem for snapshots, where resolving one of these fuzzy back
references would be O(number_of_snapshots) and quite slow.  The solution used
here is to use the fuzzy back references in the common case where a given tree
block is only referenced by one root, and use the full back references when
multiple roots have a reference

1 files changed, 144 insertions, 15 deletions

diff --git a/print-tree.c b/print-tree.c
index 86033cf3..59f43588 100644
--- a/print-tree.c
+++ b/print-tree.c
@@ -159,6 +159,107 @@ static void print_file_extent_item(struct extent_buffer *eb,
 	       btrfs_file_extent_compression(eb, fi));
 }
 
+static void print_extent_item(struct extent_buffer *eb, int slot)
+{
+	struct btrfs_extent_item *ei;
+	struct btrfs_extent_inline_ref *iref;
+	struct btrfs_extent_data_ref *dref;
+	struct btrfs_shared_data_ref *sref;
+	struct btrfs_disk_key key;
+	unsigned long end;
+	unsigned long ptr;
+	int type;
+	u32 item_size = btrfs_item_size_nr(eb, slot);
+	u64 flags;
+	u64 offset;
+
+	if (item_size < sizeof(*ei)) {
+#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
+		struct btrfs_extent_item_v0 *ei0;
+		BUG_ON(item_size != sizeof(*ei0));
+		ei0 = btrfs_item_ptr(eb, slot, struct btrfs_extent_item_v0);
+		printf("\t\textent refs %u\n",
+		       btrfs_extent_refs_v0(eb, ei0));
+		return;
+#else
+		BUG();
+#endif
+	}
+
+	ei = btrfs_item_ptr(eb, slot, struct btrfs_extent_item);
+	flags = btrfs_extent_flags(eb, ei);
+
+	printf("\t\textent refs %llu gen %llu flags %llu\n",
+	       (unsigned long long)btrfs_extent_refs(eb, ei),
+	       (unsigned long long)btrfs_extent_generation(eb, ei),
+	       (unsigned long long)flags);
+
+	if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
+		struct btrfs_tree_block_info *info;
+		info = (struct btrfs_tree_block_info *)(ei + 1);
+		btrfs_tree_block_key(eb, info, &key);
+		printf("\t\ttree block key (%llu %x %llu) level %d\n",
+		       (unsigned long long)btrfs_disk_key_objectid(&key),
+		       key.type,
+		       (unsigned long long)btrfs_disk_key_offset(&key),
+		       btrfs_tree_block_level(eb, info));
+		iref = (struct btrfs_extent_inline_ref *)(info + 1);
+	} else {
+		iref = (struct btrfs_extent_inline_ref *)(ei + 1);
+	}
+
+	ptr = (unsigned long)iref;
+	end = (unsigned long)ei + item_size;
+	while (ptr < end) {
+		iref = (struct btrfs_extent_inline_ref *)ptr;
+		type = btrfs_extent_inline_ref_type(eb, iref);
+		offset = btrfs_extent_inline_ref_offset(eb, iref);
+		switch (type) {
+		case BTRFS_TREE_BLOCK_REF_KEY:
+			printf("\t\ttree block backref root %llu\n",
+			       (unsigned long long)offset);
+			break;
+		case BTRFS_SHARED_BLOCK_REF_KEY:
+			printf("\t\tshared block backref parent %llu\n",
+			       (unsigned long long)offset);
+			break;
+		case BTRFS_EXTENT_DATA_REF_KEY:
+			dref = (struct btrfs_extent_data_ref *)(&iref->offset);
+			printf("\t\textent data backref root %llu "
+			       "objectid %llu offset %llu count %u\n",
+			       (unsigned long long)btrfs_extent_data_ref_root(eb, dref),
+			       (unsigned long long)btrfs_extent_data_ref_objectid(eb, dref),
+			       (unsigned long long)btrfs_extent_data_ref_offset(eb, dref),
+			       btrfs_extent_data_ref_count(eb, dref));
+			break;
+		case BTRFS_SHARED_DATA_REF_KEY:
+			sref = (struct btrfs_shared_data_ref *)(iref + 1);
+			printf("\t\tshared data backref parent %llu count %u\n",
+			       (unsigned long long)offset,
+			       btrfs_shared_data_ref_count(eb, sref));
+			break;
+		default:
+			BUG();
+		}
+		ptr += btrfs_extent_inline_ref_size(type);
+	}
+	WARN_ON(ptr > end);
+}
+
+#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
+static void print_extent_ref_v0(struct extent_buffer *eb, int slot)
+{
+	struct btrfs_extent_ref_v0 *ref0;
+
+	ref0 = btrfs_item_ptr(eb, slot, struct btrfs_extent_ref_v0);
+	printf("\t\textent back ref root %llu gen %llu "
+		"owner %llu num_refs %lu\n",
+		(unsigned long long)btrfs_ref_root_v0(eb, ref0),
+		(unsigned long long)btrfs_ref_generation_v0(eb, ref0),
+		(unsigned long long)btrfs_ref_objectid_v0(eb, ref0),
+		(unsigned long)btrfs_ref_count_v0(eb, ref0));
+}
+#endif
 
 static void print_root_ref(struct extent_buffer *leaf, int slot, char *tag)
 {
@@ -214,8 +315,20 @@ static void print_key_type(u8 type)
 	case BTRFS_EXTENT_ITEM_KEY:
 		printf("EXTENT_ITEM");
 		break;
-	case BTRFS_EXTENT_REF_KEY:
-		printf("EXTENT_REF");
+	case BTRFS_TREE_BLOCK_REF_KEY:
+		printf("TREE_BLOCK_REF");
+		break;
+	case BTRFS_SHARED_BLOCK_REF_KEY:
+		printf("SHARED_BLOCK_REF");
+		break;
+	case BTRFS_EXTENT_DATA_REF_KEY:
+		printf("EXTENT_DATA_REF");
+		break;
+	case BTRFS_SHARED_DATA_REF_KEY:
+		printf("SHARED_DATA_REF");
+		break;
+	case BTRFS_EXTENT_REF_V0_KEY:
+		printf("EXTENT_REF_V0");
 		break;
 	case BTRFS_CSUM_ITEM_KEY:
 		printf("CSUM_ITEM");
@@ -324,14 +437,14 @@ void btrfs_print_leaf(struct btrfs_root *root, struct extent_buffer *l)
 	int i;
 	char *str;
 	struct btrfs_item *item;
-	struct btrfs_extent_item *ei;
 	struct btrfs_root_item *ri;
 	struct btrfs_dir_item *di;
 	struct btrfs_inode_item *ii;
 	struct btrfs_file_extent_item *fi;
 	struct btrfs_csum_item *ci;
 	struct btrfs_block_group_item *bi;
-	struct btrfs_extent_ref *ref;
+	struct btrfs_extent_data_ref *dref;
+	struct btrfs_shared_data_ref *sref;
 	struct btrfs_inode_ref *iref;
 	struct btrfs_dev_extent *dev_extent;
 	struct btrfs_disk_key disk_key;
@@ -410,18 +523,34 @@ void btrfs_print_leaf(struct btrfs_root *root, struct extent_buffer *l)
 			print_root_ref(l, i, "backref");
 			break;
 		case BTRFS_EXTENT_ITEM_KEY:
-			ei = btrfs_item_ptr(l, i, struct btrfs_extent_item);
-			printf("\t\textent data refs %u\n",
-				btrfs_extent_refs(l, ei));
+			print_extent_item(l, i);
+			break;
+		case BTRFS_TREE_BLOCK_REF_KEY:
+			printf("\t\ttree block backref\n");
 			break;
-		case BTRFS_EXTENT_REF_KEY:
-			ref = btrfs_item_ptr(l, i, struct btrfs_extent_ref);
-			printf("\t\textent back ref root %llu gen %llu "
-			       "owner %llu num_refs %lu\n",
-			       (unsigned long long)btrfs_ref_root(l, ref),
-			       (unsigned long long)btrfs_ref_generation(l, ref),
-			       (unsigned long long)btrfs_ref_objectid(l, ref),
-			       (unsigned long)btrfs_ref_num_refs(l, ref));
+		case BTRFS_SHARED_BLOCK_REF_KEY:
+			printf("\t\tshared block backref\n");
+			break;
+		case BTRFS_EXTENT_DATA_REF_KEY:
+			dref = btrfs_item_ptr(l, i, struct btrfs_extent_data_ref);
+			printf("\t\textent data backref root %llu "
+			       "objectid %llu offset %llu count %u\n",
+			       (unsigned long long)btrfs_extent_data_ref_root(l, dref),
+			       (unsigned long long)btrfs_extent_data_ref_objectid(l, dref),
+			       (unsigned long long)btrfs_extent_data_ref_offset(l, dref),
+			       btrfs_extent_data_ref_count(l, dref));
+			break;
+		case BTRFS_SHARED_DATA_REF_KEY:
+			sref = btrfs_item_ptr(l, i, struct btrfs_shared_data_ref);
+			printf("\t\tshared data backref count %u\n",
+			       btrfs_shared_data_ref_count(l, sref));
+			break;
+		case BTRFS_EXTENT_REF_V0_KEY:
+#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
+			print_extent_ref_v0(l, i);
+#else
+			BUG();
+#endif
 			break;
 		case BTRFS_CSUM_ITEM_KEY:
 			ci = btrfs_item_ptr(l, i, struct btrfs_csum_item);