bcachefs: BTREE_ID_snapshot_tree

This adds a new btree which gets us a persistent per-snapshot-tree
identifier.

 - BTREE_ID_snapshot_trees
 - KEY_TYPE_snapshot_tree
 - bch_snapshot now has a field that points to a snapshot_tree

This is going to be used to designate one snapshot ID/subvolume out of a
given tree of snapshots as the "main" subvolume, so that we can do quota
accounting in that subvolume and not the rest.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs.h

@@ -445,6 +445,7 @@ enum gc_phase {
 	GC_PHASE_BTREE_need_discard,
 	GC_PHASE_BTREE_backpointers,
 	GC_PHASE_BTREE_bucket_gens,
+	GC_PHASE_BTREE_snapshot_trees,
 
 	GC_PHASE_PENDING_DELETE,
 };

fs/bcachefs/bcachefs_format.h

@@ -364,7 +364,8 @@ static inline void bkey_init(struct bkey *k)
 	x(alloc_v4,		27)			\
 	x(backpointer,		28)			\
 	x(inode_v3,		29)			\
-	x(bucket_gens,		30)
+	x(bucket_gens,		30)			\
+	x(snapshot_tree,	31)
 
 enum bch_bkey_type {
 #define x(name, nr) KEY_TYPE_##name	= nr,
@@ -1123,7 +1124,7 @@ struct bch_snapshot {
 	__le32			parent;
 	__le32			children[2];
 	__le32			subvol;
-	__le32			pad;
+	__le32			tree;
 };
 
 LE32_BITMASK(BCH_SNAPSHOT_DELETED,	struct bch_snapshot, flags,  0,  1)
@@ -1131,6 +1132,19 @@ LE32_BITMASK(BCH_SNAPSHOT_DELETED,	struct bch_snapshot, flags,  0,  1)
 /* True if a subvolume points to this snapshot node: */
 LE32_BITMASK(BCH_SNAPSHOT_SUBVOL,	struct bch_snapshot, flags,  1,  2)
 
+/*
+ * Snapshot trees:
+ *
+ * The snapshot_trees btree gives us persistent indentifier for each tree of
+ * bch_snapshot nodes, and allow us to record and easily find the root/master
+ * subvolume that other snapshots were created from:
+ */
+struct bch_snapshot_tree {
+	struct bch_val		v;
+	__le32			master_subvol;
+	__le32			root_snapshot;
+};
+
 /* LRU btree: */
 
 struct bch_lru {
@@ -1559,7 +1573,8 @@ struct bch_sb_field_journal_seq_blacklist {
 	x(bucket_gens,			25)		\
 	x(lru_v2,			26)		\
 	x(fragmentation_lru,		27)		\
-	x(no_bps_in_alloc_keys,		28)
+	x(no_bps_in_alloc_keys,		28)		\
+	x(snapshot_trees,		29)
 
 enum bcachefs_metadata_version {
 	bcachefs_metadata_version_min = 9,
@@ -1569,6 +1584,8 @@ enum bcachefs_metadata_version {
 	bcachefs_metadata_version_max
 };
 
+static const unsigned bcachefs_metadata_required_upgrade_below = bcachefs_metadata_version_snapshot_trees;
+
 #define bcachefs_metadata_version_current	(bcachefs_metadata_version_max - 1)
 
 #define BCH_SB_SECTOR			8
@@ -2095,7 +2112,8 @@ LE32_BITMASK(JSET_NO_FLUSH,	struct jset, flags, 5, 6);
 	x(freespace,		11)		\
 	x(need_discard,		12)		\
 	x(backpointers,		13)		\
-	x(bucket_gens,		14)
+	x(bucket_gens,		14)		\
+	x(snapshot_trees,	15)
 
 enum btree_id {
 #define x(kwd, val) BTREE_ID_##kwd = val,

fs/bcachefs/bkey_methods.c

@@ -204,6 +204,9 @@ static unsigned bch2_key_types_allowed[] = {
 	[BKEY_TYPE_bucket_gens] =
 		(1U << KEY_TYPE_deleted)|
 		(1U << KEY_TYPE_bucket_gens),
+	[BKEY_TYPE_snapshot_trees] =
+		(1U << KEY_TYPE_deleted)|
+		(1U << KEY_TYPE_snapshot_tree),
 	[BKEY_TYPE_btree] =
 		(1U << KEY_TYPE_deleted)|
 		(1U << KEY_TYPE_btree_ptr)|

fs/bcachefs/errcode.h

@@ -93,6 +93,7 @@
 	x(ENOSPC,			ENOSPC_sb_members)			\
 	x(ENOSPC,			ENOSPC_sb_crypt)			\
 	x(ENOSPC,			ENOSPC_btree_slot)			\
+	x(ENOSPC,			ENOSPC_snapshot_tree)			\
 	x(0,				open_buckets_empty)			\
 	x(0,				freelist_empty)				\
 	x(BCH_ERR_freelist_empty,	no_buckets_found)			\

fs/bcachefs/fsck.c

@@ -2427,7 +2427,8 @@ int bch2_fsck_full(struct bch_fs *c)
 {
 	int ret;
 again:
-	ret =   bch2_fs_check_snapshots(c) ?:
+	ret =   bch2_fs_check_snapshot_trees(c);
+		bch2_fs_check_snapshots(c) ?:
 		bch2_fs_check_subvols(c) ?:
 		bch2_delete_dead_snapshots(c) ?:
 		check_inodes(c, true) ?:

fs/bcachefs/recovery.c

@@ -1025,16 +1025,25 @@ static int read_btree_roots(struct bch_fs *c)
 
 static int bch2_fs_initialize_subvolumes(struct bch_fs *c)
 {
-	struct bkey_i_snapshot	root_snapshot;
-	struct bkey_i_subvolume root_volume;
+	struct bkey_i_snapshot_tree	root_tree;
+	struct bkey_i_snapshot		root_snapshot;
+	struct bkey_i_subvolume		root_volume;
 	int ret;
 
+	bkey_snapshot_tree_init(&root_tree.k_i);
+	root_tree.k.p.offset		= 1;
+	root_tree.v.master_subvol	= cpu_to_le32(1);
+	root_tree.v.root_snapshot	= cpu_to_le32(U32_MAX);
+	ret = bch2_btree_insert(c, BTREE_ID_snapshot_trees,
+				&root_tree.k_i,
+				NULL, NULL, 0);
+
 	bkey_snapshot_init(&root_snapshot.k_i);
 	root_snapshot.k.p.offset = U32_MAX;
 	root_snapshot.v.flags	= 0;
 	root_snapshot.v.parent	= 0;
 	root_snapshot.v.subvol	= BCACHEFS_ROOT_SUBVOL;
-	root_snapshot.v.pad	= 0;
+	root_snapshot.v.tree	= cpu_to_le32(1);
 	SET_BCH_SNAPSHOT_SUBVOL(&root_snapshot.v, true);
 
 	ret = bch2_btree_insert(c, BTREE_ID_snapshots,
@@ -1135,8 +1144,12 @@ int bch2_fs_recovery(struct bch_fs *c)
 	}
 
 	if (!c->opts.nochanges) {
-		if (c->sb.version < bcachefs_metadata_version_no_bps_in_alloc_keys) {
-			bch_info(c, "version prior to no_bps_in_alloc_keys, upgrade and fsck required");
+		if (c->sb.version < bcachefs_metadata_required_upgrade_below) {
+			bch_info(c, "version %s (%u) prior to %s (%u), upgrade and fsck required",
+				 bch2_metadata_versions[c->sb.version],
+				 c->sb.version,
+				 bch2_metadata_versions[bcachefs_metadata_required_upgrade_below],
+				 bcachefs_metadata_required_upgrade_below);
 			c->opts.version_upgrade	= true;
 			c->opts.fsck		= true;
 			c->opts.fix_errors	= FSCK_OPT_YES;

fs/bcachefs/subvolume.h

@@ -5,6 +5,16 @@
 #include "darray.h"
 #include "subvolume_types.h"
 
+void bch2_snapshot_tree_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
+int bch2_snapshot_tree_invalid(const struct bch_fs *, struct bkey_s_c,
+			       unsigned, struct printbuf *);
+
+#define bch2_bkey_ops_snapshot_tree ((struct bkey_ops) {	\
+	.key_invalid	= bch2_snapshot_tree_invalid,		\
+	.val_to_text	= bch2_snapshot_tree_to_text,		\
+	.min_val_size	= 8,					\
+})
+
 void bch2_snapshot_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
 int bch2_snapshot_invalid(const struct bch_fs *, struct bkey_s_c,
 			  unsigned, struct printbuf *);
@@ -28,6 +38,15 @@ static inline u32 bch2_snapshot_parent(struct bch_fs *c, u32 id)
 	return snapshot_t(c, id)->parent;
 }
 
+static inline u32 bch2_snapshot_root(struct bch_fs *c, u32 id)
+{
+	u32 parent;
+
+	while ((parent = bch2_snapshot_parent(c, id)))
+		id = parent;
+	return id;
+}
+
 static inline u32 bch2_snapshot_equiv(struct bch_fs *c, u32 id)
 {
 	return snapshot_t(c, id)->equiv;
@@ -107,6 +126,7 @@ static inline int snapshot_list_add(struct bch_fs *c, snapshot_id_list *s, u32 i
 	return ret;
 }
 
+int bch2_fs_check_snapshot_trees(struct bch_fs *);
 int bch2_fs_check_snapshots(struct bch_fs *);
 int bch2_fs_check_subvols(struct bch_fs *);
 

fs/bcachefs/subvolume_types.h

@@ -10,6 +10,7 @@ struct snapshot_t {
 	u32			parent;
 	u32			children[2];
 	u32			subvol; /* Nonzero only if a subvolume points to this node: */
+	u32			tree;
 	u32			equiv;
 };