bcachefs: Split out snapshot.c

subvolume.c has gotten a bit large, this splits out a separate file just
for managing snapshot trees - BTREE_ID_snapshots.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 19 insertions, 1341 deletions

diff --git a/fs/bcachefs/subvolume.c b/fs/bcachefs/subvolume.c
index 7de6fe0cdd43..0214a98deb4f 100644
--- a/fs/bcachefs/subvolume.c
+++ b/fs/bcachefs/subvolume.c
@@ -6,885 +6,13 @@
 #include "errcode.h"
 #include "error.h"
 #include "fs.h"
+#include "snapshot.h"
 #include "subvolume.h"
 
 #include <linux/random.h>
 
 static int bch2_subvolume_delete(struct btree_trans *, u32);
 
-static inline u32 get_ancestor_below(struct snapshot_table *t, u32 id, u32 ancestor)
-{
-	const struct snapshot_t *s = __snapshot_t(t, id);
-
-	if (s->skip[2] <= ancestor)
-		return s->skip[2];
-	if (s->skip[1] <= ancestor)
-		return s->skip[1];
-	if (s->skip[0] <= ancestor)
-		return s->skip[0];
-	return s->parent;
-}
-
-bool __bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
-{
-	struct snapshot_table *t;
-	bool ret;
-
-	EBUG_ON(c->curr_recovery_pass <= BCH_RECOVERY_PASS_check_snapshots);
-
-	rcu_read_lock();
-	t = rcu_dereference(c->snapshots);
-
-	while (id && id < ancestor - IS_ANCESTOR_BITMAP)
-		id = get_ancestor_below(t, id, ancestor);
-
-	ret = id && id < ancestor
-		? test_bit(ancestor - id - 1, __snapshot_t(t, id)->is_ancestor)
-		: id == ancestor;
-	rcu_read_unlock();
-
-	return ret;
-}
-
-static bool bch2_snapshot_is_ancestor_early(struct bch_fs *c, u32 id, u32 ancestor)
-{
-	struct snapshot_table *t;
-
-	rcu_read_lock();
-	t = rcu_dereference(c->snapshots);
-
-	while (id && id < ancestor)
-		id = __snapshot_t(t, id)->parent;
-	rcu_read_unlock();
-
-	return id == ancestor;
-}
-
-static inline u32 bch2_snapshot_depth(struct bch_fs *c, u32 parent)
-{
-	u32 depth;
-
-	rcu_read_lock();
-	depth = parent ? snapshot_t(c, parent)->depth + 1 : 0;
-	rcu_read_unlock();
-
-	return depth;
-}
-
-struct snapshot_t_free_rcu {
-	struct rcu_head		rcu;
-	struct snapshot_table	*t;
-};
-
-static void snapshot_t_free_rcu(struct rcu_head *rcu)
-{
-	struct snapshot_t_free_rcu *free_rcu =
-		container_of(rcu, struct snapshot_t_free_rcu, rcu);
-
-	kvfree(free_rcu->t);
-	kfree(free_rcu);
-}
-
-static noinline struct snapshot_t *__snapshot_t_mut(struct bch_fs *c, u32 id)
-{
-	size_t idx = U32_MAX - id;
-	size_t new_size;
-	struct snapshot_table *new, *old;
-
-	new_size = max(16UL, roundup_pow_of_two(idx + 1));
-
-	new = kvzalloc(struct_size(new, s, new_size), GFP_KERNEL);
-	if (!new)
-		return NULL;
-
-	old = rcu_dereference_protected(c->snapshots, true);
-	if (old)
-		memcpy(new->s,
-		       rcu_dereference_protected(c->snapshots, true)->s,
-		       sizeof(new->s[0]) * c->snapshot_table_size);
-
-	rcu_assign_pointer(c->snapshots, new);
-	c->snapshot_table_size = new_size;
-	if (old) {
-		struct snapshot_t_free_rcu *rcu =
-			kmalloc(sizeof(*rcu), GFP_KERNEL|__GFP_NOFAIL);
-
-		rcu->t = old;
-		call_rcu(&rcu->rcu, snapshot_t_free_rcu);
-	}
-
-	return &rcu_dereference_protected(c->snapshots, true)->s[idx];
-}
-
-static inline struct snapshot_t *snapshot_t_mut(struct bch_fs *c, u32 id)
-{
-	size_t idx = U32_MAX - id;
-
-	lockdep_assert_held(&c->snapshot_table_lock);
-
-	if (likely(idx < c->snapshot_table_size))
-		return &rcu_dereference_protected(c->snapshots, true)->s[idx];
-
-	return __snapshot_t_mut(c, id);
-}
-
-/* Snapshot tree: */
-
-void bch2_snapshot_tree_to_text(struct printbuf *out, struct bch_fs *c,
-				struct bkey_s_c k)
-{
-	struct bkey_s_c_snapshot_tree t = bkey_s_c_to_snapshot_tree(k);
-
-	prt_printf(out, "subvol %u root snapshot %u",
-		   le32_to_cpu(t.v->master_subvol),
-		   le32_to_cpu(t.v->root_snapshot));
-}
-
-int bch2_snapshot_tree_invalid(const struct bch_fs *c, struct bkey_s_c k,
-			       enum bkey_invalid_flags flags,
-			       struct printbuf *err)
-{
-	if (bkey_gt(k.k->p, POS(0, U32_MAX)) ||
-	    bkey_lt(k.k->p, POS(0, 1))) {
-		prt_printf(err, "bad pos");
-		return -BCH_ERR_invalid_bkey;
-	}
-
-	return 0;
-}
-
-int bch2_snapshot_tree_lookup(struct btree_trans *trans, u32 id,
-			      struct bch_snapshot_tree *s)
-{
-	int ret = bch2_bkey_get_val_typed(trans, BTREE_ID_snapshot_trees, POS(0, id),
-					  BTREE_ITER_WITH_UPDATES, snapshot_tree, s);
-
-	if (bch2_err_matches(ret, ENOENT))
-		ret = -BCH_ERR_ENOENT_snapshot_tree;
-	return ret;
-}
-
-static struct bkey_i_snapshot_tree *
-__snapshot_tree_create(struct btree_trans *trans)
-{
-	struct btree_iter iter;
-	int ret = bch2_bkey_get_empty_slot(trans, &iter,
-			BTREE_ID_snapshot_trees, POS(0, U32_MAX));
-	struct bkey_i_snapshot_tree *s_t;
-
-	if (ret == -BCH_ERR_ENOSPC_btree_slot)
-		ret = -BCH_ERR_ENOSPC_snapshot_tree;
-	if (ret)
-		return ERR_PTR(ret);
-
-	s_t = bch2_bkey_alloc(trans, &iter, 0, snapshot_tree);
-	ret = PTR_ERR_OR_ZERO(s_t);
-	bch2_trans_iter_exit(trans, &iter);
-	return ret ? ERR_PTR(ret) : s_t;
-}
-
-static int snapshot_tree_create(struct btree_trans *trans,
-				u32 root_id, u32 subvol_id, u32 *tree_id)
-{
-	struct bkey_i_snapshot_tree *n_tree =
-		__snapshot_tree_create(trans);
-
-	if (IS_ERR(n_tree))
-		return PTR_ERR(n_tree);
-
-	n_tree->v.master_subvol	= cpu_to_le32(subvol_id);
-	n_tree->v.root_snapshot	= cpu_to_le32(root_id);
-	*tree_id = n_tree->k.p.offset;
-	return 0;
-}
-
-/* Snapshot nodes: */
-
-void bch2_snapshot_to_text(struct printbuf *out, struct bch_fs *c,
-			   struct bkey_s_c k)
-{
-	struct bkey_s_c_snapshot s = bkey_s_c_to_snapshot(k);
-
-	prt_printf(out, "is_subvol %llu deleted %llu parent %10u children %10u %10u subvol %u tree %u",
-	       BCH_SNAPSHOT_SUBVOL(s.v),
-	       BCH_SNAPSHOT_DELETED(s.v),
-	       le32_to_cpu(s.v->parent),
-	       le32_to_cpu(s.v->children[0]),
-	       le32_to_cpu(s.v->children[1]),
-	       le32_to_cpu(s.v->subvol),
-	       le32_to_cpu(s.v->tree));
-
-	if (bkey_val_bytes(k.k) > offsetof(struct bch_snapshot, depth))
-		prt_printf(out, " depth %u skiplist %u %u %u",
-			   le32_to_cpu(s.v->depth),
-			   le32_to_cpu(s.v->skip[0]),
-			   le32_to_cpu(s.v->skip[1]),
-			   le32_to_cpu(s.v->skip[2]));
-}
-
-int bch2_snapshot_invalid(const struct bch_fs *c, struct bkey_s_c k,
-			  enum bkey_invalid_flags flags,
-			  struct printbuf *err)
-{
-	struct bkey_s_c_snapshot s;
-	u32 i, id;
-
-	if (bkey_gt(k.k->p, POS(0, U32_MAX)) ||
-	    bkey_lt(k.k->p, POS(0, 1))) {
-		prt_printf(err, "bad pos");
-		return -BCH_ERR_invalid_bkey;
-	}
-
-	s = bkey_s_c_to_snapshot(k);
-
-	id = le32_to_cpu(s.v->parent);
-	if (id && id <= k.k->p.offset) {
-		prt_printf(err, "bad parent node (%u <= %llu)",
-		       id, k.k->p.offset);
-		return -BCH_ERR_invalid_bkey;
-	}
-
-	if (le32_to_cpu(s.v->children[0]) < le32_to_cpu(s.v->children[1])) {
-		prt_printf(err, "children not normalized");
-		return -BCH_ERR_invalid_bkey;
-	}
-
-	if (s.v->children[0] &&
-	    s.v->children[0] == s.v->children[1]) {
-		prt_printf(err, "duplicate child nodes");
-		return -BCH_ERR_invalid_bkey;
-	}
-
-	for (i = 0; i < 2; i++) {
-		id = le32_to_cpu(s.v->children[i]);
-
-		if (id >= k.k->p.offset) {
-			prt_printf(err, "bad child node (%u >= %llu)",
-			       id, k.k->p.offset);
-			return -BCH_ERR_invalid_bkey;
-		}
-	}
-
-	if (bkey_val_bytes(k.k) > offsetof(struct bch_snapshot, skip)) {
-		if (le32_to_cpu(s.v->skip[0]) > le32_to_cpu(s.v->skip[1]) ||
-		    le32_to_cpu(s.v->skip[1]) > le32_to_cpu(s.v->skip[2])) {
-			prt_printf(err, "skiplist not normalized");
-			return -BCH_ERR_invalid_bkey;
-		}
-
-		for (i = 0; i < ARRAY_SIZE(s.v->skip); i++) {
-			id = le32_to_cpu(s.v->skip[i]);
-
-			if (!id != !s.v->parent ||
-			    (s.v->parent &&
-			     id <= k.k->p.offset)) {
-				prt_printf(err, "bad skiplist node %u)", id);
-				return -BCH_ERR_invalid_bkey;
-			}
-		}
-	}
-
-	return 0;
-}
-
-int bch2_mark_snapshot(struct btree_trans *trans,
-		       enum btree_id btree, unsigned level,
-		       struct bkey_s_c old, struct bkey_s_c new,
-		       unsigned flags)
-{
-	struct bch_fs *c = trans->c;
-	struct snapshot_t *t;
-	u32 id = new.k->p.offset;
-	int ret = 0;
-
-	mutex_lock(&c->snapshot_table_lock);
-
-	t = snapshot_t_mut(c, id);
-	if (!t) {
-		ret = -BCH_ERR_ENOMEM_mark_snapshot;
-		goto err;
-	}
-
-	if (new.k->type == KEY_TYPE_snapshot) {
-		struct bkey_s_c_snapshot s = bkey_s_c_to_snapshot(new);
-		u32 parent = id;
-
-		t->parent	= le32_to_cpu(s.v->parent);
-		t->children[0]	= le32_to_cpu(s.v->children[0]);
-		t->children[1]	= le32_to_cpu(s.v->children[1]);
-		t->subvol	= BCH_SNAPSHOT_SUBVOL(s.v) ? le32_to_cpu(s.v->subvol) : 0;
-		t->tree		= le32_to_cpu(s.v->tree);
-
-		if (bkey_val_bytes(s.k) > offsetof(struct bch_snapshot, depth)) {
-			t->depth	= le32_to_cpu(s.v->depth);
-			t->skip[0]	= le32_to_cpu(s.v->skip[0]);
-			t->skip[1]	= le32_to_cpu(s.v->skip[1]);
-			t->skip[2]	= le32_to_cpu(s.v->skip[2]);
-		} else {
-			t->depth	= 0;
-			t->skip[0]	= 0;
-			t->skip[1]	= 0;
-			t->skip[2]	= 0;
-		}
-
-		while ((parent = bch2_snapshot_parent_early(c, parent)) &&
-		       parent - id - 1 < IS_ANCESTOR_BITMAP)
-			__set_bit(parent - id - 1, t->is_ancestor);
-
-		if (BCH_SNAPSHOT_DELETED(s.v)) {
-			set_bit(BCH_FS_HAVE_DELETED_SNAPSHOTS, &c->flags);
-			c->recovery_passes_explicit |= BIT_ULL(BCH_RECOVERY_PASS_delete_dead_snapshots);
-		}
-	} else {
-		memset(t, 0, sizeof(*t));
-	}
-err:
-	mutex_unlock(&c->snapshot_table_lock);
-	return ret;
-}
-
-static int snapshot_lookup(struct btree_trans *trans, u32 id,
-			   struct bch_snapshot *s)
-{
-	return bch2_bkey_get_val_typed(trans, BTREE_ID_snapshots, POS(0, id),
-				       BTREE_ITER_WITH_UPDATES, snapshot, s);
-}
-
-static int snapshot_live(struct btree_trans *trans, u32 id)
-{
-	struct bch_snapshot v;
-	int ret;
-
-	if (!id)
-		return 0;
-
-	ret = snapshot_lookup(trans, id, &v);
-	if (bch2_err_matches(ret, ENOENT))
-		bch_err(trans->c, "snapshot node %u not found", id);
-	if (ret)
-		return ret;
-
-	return !BCH_SNAPSHOT_DELETED(&v);
-}
-
-static int bch2_snapshot_set_equiv(struct btree_trans *trans, struct bkey_s_c k)
-{
-	struct bch_fs *c = trans->c;
-	unsigned i, nr_live = 0, live_idx = 0;
-	struct bkey_s_c_snapshot snap;
-	u32 id = k.k->p.offset, child[2];
-
-	if (k.k->type != KEY_TYPE_snapshot)
-		return 0;
-
-	snap = bkey_s_c_to_snapshot(k);
-
-	child[0] = le32_to_cpu(snap.v->children[0]);
-	child[1] = le32_to_cpu(snap.v->children[1]);
-
-	for (i = 0; i < 2; i++) {
-		int ret = snapshot_live(trans, child[i]);
-
-		if (ret < 0)
-			return ret;
-
-		if (ret)
-			live_idx = i;
-		nr_live += ret;
-	}
-
-	mutex_lock(&c->snapshot_table_lock);
-
-	snapshot_t_mut(c, id)->equiv = nr_live == 1
-		? snapshot_t_mut(c, child[live_idx])->equiv
-		: id;
-
-	mutex_unlock(&c->snapshot_table_lock);
-
-	return 0;
-}
-
-/* fsck: */
-
-static u32 bch2_snapshot_child(struct bch_fs *c, u32 id, unsigned child)
-{
-	return snapshot_t(c, id)->children[child];
-}
-
-static u32 bch2_snapshot_left_child(struct bch_fs *c, u32 id)
-{
-	return bch2_snapshot_child(c, id, 0);
-}
-
-static u32 bch2_snapshot_right_child(struct bch_fs *c, u32 id)
-{
-	return bch2_snapshot_child(c, id, 1);
-}
-
-static u32 bch2_snapshot_tree_next(struct bch_fs *c, u32 id)
-{
-	u32 n, parent;
-
-	n = bch2_snapshot_left_child(c, id);
-	if (n)
-		return n;
-
-	while ((parent = bch2_snapshot_parent(c, id))) {
-		n = bch2_snapshot_right_child(c, parent);
-		if (n && n != id)
-			return n;
-		id = parent;
-	}
-
-	return 0;
-}
-
-static u32 bch2_snapshot_tree_oldest_subvol(struct bch_fs *c, u32 snapshot_root)
-{
-	u32 id = snapshot_root;
-	u32 subvol = 0, s;
-
-	while (id) {
-		s = snapshot_t(c, id)->subvol;
-
-		if (s && (!subvol || s < subvol))
-			subvol = s;
-
-		id = bch2_snapshot_tree_next(c, id);
-	}
-
-	return subvol;
-}
-
-static int bch2_snapshot_tree_master_subvol(struct btree_trans *trans,
-					    u32 snapshot_root, u32 *subvol_id)
-{
-	struct bch_fs *c = trans->c;
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	struct bkey_s_c_subvolume s;
-	bool found = false;
-	int ret;
-
-	for_each_btree_key_norestart(trans, iter, BTREE_ID_subvolumes, POS_MIN,
-				     0, k, ret) {
-		if (k.k->type != KEY_TYPE_subvolume)
-			continue;
-
-		s = bkey_s_c_to_subvolume(k);
-		if (!bch2_snapshot_is_ancestor(c, le32_to_cpu(s.v->snapshot), snapshot_root))
-			continue;
-		if (!BCH_SUBVOLUME_SNAP(s.v)) {
-			*subvol_id = s.k->p.offset;
-			found = true;
-			break;
-		}
-	}
-
-	bch2_trans_iter_exit(trans, &iter);
-
-	if (!ret && !found) {
-		struct bkey_i_subvolume *s;
-
-		*subvol_id = bch2_snapshot_tree_oldest_subvol(c, snapshot_root);
-
-		s = bch2_bkey_get_mut_typed(trans, &iter,
-					    BTREE_ID_subvolumes, POS(0, *subvol_id),
-					    0, subvolume);
-		ret = PTR_ERR_OR_ZERO(s);
-		if (ret)
-			return ret;
-
-		SET_BCH_SUBVOLUME_SNAP(&s->v, false);
-	}
-
-	return ret;
-}
-
-static int check_snapshot_tree(struct btree_trans *trans,
-			       struct btree_iter *iter,
-			       struct bkey_s_c k)
-{
-	struct bch_fs *c = trans->c;
-	struct bkey_s_c_snapshot_tree st;
-	struct bch_snapshot s;
-	struct bch_subvolume subvol;
-	struct printbuf buf = PRINTBUF;
-	u32 root_id;
-	int ret;
-
-	if (k.k->type != KEY_TYPE_snapshot_tree)
-		return 0;
-
-	st = bkey_s_c_to_snapshot_tree(k);
-	root_id = le32_to_cpu(st.v->root_snapshot);
-
-	ret = snapshot_lookup(trans, root_id, &s);
-	if (ret && !bch2_err_matches(ret, ENOENT))
-		goto err;
-
-	if (fsck_err_on(ret ||
-			root_id != bch2_snapshot_root(c, root_id) ||
-			st.k->p.offset != le32_to_cpu(s.tree),
-			c,
-			"snapshot tree points to missing/incorrect snapshot:\n  %s",
-			(bch2_bkey_val_to_text(&buf, c, st.s_c), buf.buf))) {
-		ret = bch2_btree_delete_at(trans, iter, 0);
-		goto err;
-	}
-
-	ret = bch2_subvolume_get(trans, le32_to_cpu(st.v->master_subvol),
-				 false, 0, &subvol);
-	if (ret && !bch2_err_matches(ret, ENOENT))
-		goto err;
-
-	if (fsck_err_on(ret, c,
-			"snapshot tree points to missing subvolume:\n  %s",
-			(printbuf_reset(&buf),
-			 bch2_bkey_val_to_text(&buf, c, st.s_c), buf.buf)) ||
-	    fsck_err_on(!bch2_snapshot_is_ancestor_early(c,
-						le32_to_cpu(subvol.snapshot),
-						root_id), c,
-			"snapshot tree points to subvolume that does not point to snapshot in this tree:\n  %s",
-			(printbuf_reset(&buf),
-			 bch2_bkey_val_to_text(&buf, c, st.s_c), buf.buf)) ||
-	    fsck_err_on(BCH_SUBVOLUME_SNAP(&subvol), c,
-			"snapshot tree points to snapshot subvolume:\n  %s",
-			(printbuf_reset(&buf),
-			 bch2_bkey_val_to_text(&buf, c, st.s_c), buf.buf))) {
-		struct bkey_i_snapshot_tree *u;
-		u32 subvol_id;
-
-		ret = bch2_snapshot_tree_master_subvol(trans, root_id, &subvol_id);
-		if (ret)
-			goto err;
-
-		u = bch2_bkey_make_mut_typed(trans, iter, &k, 0, snapshot_tree);
-		ret = PTR_ERR_OR_ZERO(u);
-		if (ret)
-			goto err;
-
-		u->v.master_subvol = cpu_to_le32(subvol_id);
-		st = snapshot_tree_i_to_s_c(u);
-	}
-err:
-fsck_err:
-	printbuf_exit(&buf);
-	return ret;
-}
-
-/*
- * For each snapshot_tree, make sure it points to the root of a snapshot tree
- * and that snapshot entry points back to it, or delete it.
- *
- * And, make sure it points to a subvolume within that snapshot tree, or correct
- * it to point to the oldest subvolume within that snapshot tree.
- */
-int bch2_check_snapshot_trees(struct bch_fs *c)
-{
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	int ret;
-
-	ret = bch2_trans_run(c,
-		for_each_btree_key_commit(&trans, iter,
-			BTREE_ID_snapshot_trees, POS_MIN,
-			BTREE_ITER_PREFETCH, k,
-			NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
-		check_snapshot_tree(&trans, &iter, k)));
-
-	if (ret)
-		bch_err(c, "error %i checking snapshot trees", ret);
-	return ret;
-}
-
-/*
- * Look up snapshot tree for @tree_id and find root,
- * make sure @snap_id is a descendent:
- */
-static int snapshot_tree_ptr_good(struct btree_trans *trans,
-				  u32 snap_id, u32 tree_id)
-{
-	struct bch_snapshot_tree s_t;
-	int ret = bch2_snapshot_tree_lookup(trans, tree_id, &s_t);
-
-	if (bch2_err_matches(ret, ENOENT))
-		return 0;
-	if (ret)
-		return ret;
-
-	return bch2_snapshot_is_ancestor_early(trans->c, snap_id, le32_to_cpu(s_t.root_snapshot));
-}
-
-static u32 snapshot_skiplist_get(struct bch_fs *c, u32 id)
-{
-	const struct snapshot_t *s;
-
-	if (!id)
-		return 0;
-
-	rcu_read_lock();
-	s = snapshot_t(c, id);
-	if (s->parent)
-		id = bch2_snapshot_nth_parent(c, id, get_random_u32_below(s->depth));
-	rcu_read_unlock();
-
-	return id;
-}
-
-static int snapshot_skiplist_good(struct btree_trans *trans, struct bch_snapshot s)
-{
-	struct bch_snapshot a;
-	unsigned i;
-	int ret;
-
-	for (i = 0; i < 3; i++) {
-		if (!s.parent != !s.skip[i])
-			return false;
-
-		if (!s.parent)
-			continue;
-
-		ret = snapshot_lookup(trans, le32_to_cpu(s.skip[i]), &a);
-		if (bch2_err_matches(ret, ENOENT))
-			return false;
-		if (ret)
-			return ret;
-
-		if (a.tree != s.tree)
-			return false;
-	}
-
-	return true;
-}
-
-/*
- * snapshot_tree pointer was incorrect: look up root snapshot node, make sure
- * its snapshot_tree pointer is correct (allocate new one if necessary), then
- * update this node's pointer to root node's pointer:
- */
-static int snapshot_tree_ptr_repair(struct btree_trans *trans,
-				    struct btree_iter *iter,
-				    struct bkey_s_c k,
-				    struct bch_snapshot *s)
-{
-	struct bch_fs *c = trans->c;
-	struct btree_iter root_iter;
-	struct bch_snapshot_tree s_t;
-	struct bkey_s_c_snapshot root;
-	struct bkey_i_snapshot *u;
-	u32 root_id = bch2_snapshot_root(c, k.k->p.offset), tree_id;
-	int ret;
-
-	root = bch2_bkey_get_iter_typed(trans, &root_iter,
-			       BTREE_ID_snapshots, POS(0, root_id),
-			       BTREE_ITER_WITH_UPDATES, snapshot);
-	ret = bkey_err(root);
-	if (ret)
-		goto err;
-
-	tree_id = le32_to_cpu(root.v->tree);
-
-	ret = bch2_snapshot_tree_lookup(trans, tree_id, &s_t);
-	if (ret && !bch2_err_matches(ret, ENOENT))
-		return ret;
-
-	if (ret || le32_to_cpu(s_t.root_snapshot) != root_id) {
-		u = bch2_bkey_make_mut_typed(trans, &root_iter, &root.s_c, 0, snapshot);
-		ret =   PTR_ERR_OR_ZERO(u) ?:
-			snapshot_tree_create(trans, root_id,
-				bch2_snapshot_tree_oldest_subvol(c, root_id),
-				&tree_id);
-		if (ret)
-			goto err;
-
-		u->v.tree = cpu_to_le32(tree_id);
-		if (k.k->p.offset == root_id)
-			*s = u->v;
-	}
-
-	if (k.k->p.offset != root_id) {
-		u = bch2_bkey_make_mut_typed(trans, iter, &k, 0, snapshot);
-		ret = PTR_ERR_OR_ZERO(u);
-		if (ret)
-			goto err;
-
-		u->v.tree = cpu_to_le32(tree_id);
-		*s = u->v;
-	}
-err:
-	bch2_trans_iter_exit(trans, &root_iter);
-	return ret;
-}
-
-static int cmp_le32(__le32 l, __le32 r)
-{
-	return cmp_int(le32_to_cpu(l), le32_to_cpu(r));
-}
-
-static int check_snapshot(struct btree_trans *trans,
-			  struct btree_iter *iter,
-			  struct bkey_s_c k)
-{
-	struct bch_fs *c = trans->c;
-	struct bch_snapshot s;
-	struct bch_subvolume subvol;
-	struct bch_snapshot v;
-	struct bkey_i_snapshot *u;
-	u32 parent_id = bch2_snapshot_parent_early(c, k.k->p.offset);
-	u32 real_depth;
-	struct printbuf buf = PRINTBUF;
-	bool should_have_subvol;
-	u32 i, id;
-	int ret = 0;
-
-	if (k.k->type != KEY_TYPE_snapshot)
-		return 0;
-
-	memset(&s, 0, sizeof(s));
-	memcpy(&s, k.v, bkey_val_bytes(k.k));
-
-	id = le32_to_cpu(s.parent);
-	if (id) {
-		ret = snapshot_lookup(trans, id, &v);
-		if (bch2_err_matches(ret, ENOENT))
-			bch_err(c, "snapshot with nonexistent parent:\n  %s",
-				(bch2_bkey_val_to_text(&buf, c, k), buf.buf));
-		if (ret)
-			goto err;
-
-		if (le32_to_cpu(v.children[0]) != k.k->p.offset &&
-		    le32_to_cpu(v.children[1]) != k.k->p.offset) {
-			bch_err(c, "snapshot parent %u missing pointer to child %llu",
-				id, k.k->p.offset);
-			ret = -EINVAL;
-			goto err;
-		}
-	}
-
-	for (i = 0; i < 2 && s.children[i]; i++) {
-		id = le32_to_cpu(s.children[i]);
-
-		ret = snapshot_lookup(trans, id, &v);
-		if (bch2_err_matches(ret, ENOENT))
-			bch_err(c, "snapshot node %llu has nonexistent child %u",
-				k.k->p.offset, id);
-		if (ret)
-			goto err;
-
-		if (le32_to_cpu(v.parent) != k.k->p.offset) {
-			bch_err(c, "snapshot child %u has wrong parent (got %u should be %llu)",
-				id, le32_to_cpu(v.parent), k.k->p.offset);
-			ret = -EINVAL;
-			goto err;
-		}
-	}
-
-	should_have_subvol = BCH_SNAPSHOT_SUBVOL(&s) &&
-		!BCH_SNAPSHOT_DELETED(&s);
-
-	if (should_have_subvol) {
-		id = le32_to_cpu(s.subvol);
-		ret = bch2_subvolume_get(trans, id, 0, false, &subvol);
-		if (bch2_err_matches(ret, ENOENT))
-			bch_err(c, "snapshot points to nonexistent subvolume:\n  %s",
-				(bch2_bkey_val_to_text(&buf, c, k), buf.buf));
-		if (ret)
-			goto err;
-
-		if (BCH_SNAPSHOT_SUBVOL(&s) != (le32_to_cpu(subvol.snapshot) == k.k->p.offset)) {
-			bch_err(c, "snapshot node %llu has wrong BCH_SNAPSHOT_SUBVOL",
-				k.k->p.offset);
-			ret = -EINVAL;
-			goto err;
-		}
-	} else {
-		if (fsck_err_on(s.subvol, c, "snapshot should not point to subvol:\n  %s",
-				(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
-			u = bch2_bkey_make_mut_typed(trans, iter, &k, 0, snapshot);
-			ret = PTR_ERR_OR_ZERO(u);
-			if (ret)
-				goto err;
-
-			u->v.subvol = 0;
-			s = u->v;
-		}
-	}
-
-	ret = snapshot_tree_ptr_good(trans, k.k->p.offset, le32_to_cpu(s.tree));
-	if (ret < 0)
-		goto err;
-
-	if (fsck_err_on(!ret, c, "snapshot points to missing/incorrect tree:\n  %s",
-			(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
-		ret = snapshot_tree_ptr_repair(trans, iter, k, &s);
-		if (ret)
-			goto err;
-	}
-	ret = 0;
-
-	real_depth = bch2_snapshot_depth(c, parent_id);
-
-	if (le32_to_cpu(s.depth) != real_depth &&
-	    (c->sb.version_upgrade_complete < bcachefs_metadata_version_snapshot_skiplists ||
-	     fsck_err(c, "snapshot with incorrect depth field, should be %u:\n  %s",
-		      real_depth, (bch2_bkey_val_to_text(&buf, c, k), buf.buf)))) {
-		u = bch2_bkey_make_mut_typed(trans, iter, &k, 0, snapshot);
-		ret = PTR_ERR_OR_ZERO(u);
-		if (ret)
-			goto err;
-
-		u->v.depth = cpu_to_le32(real_depth);
-		s = u->v;
-	}
-
-	ret = snapshot_skiplist_good(trans, s);
-	if (ret < 0)
-		goto err;
-
-	if (!ret &&
-	    (c->sb.version_upgrade_complete < bcachefs_metadata_version_snapshot_skiplists ||
-	     fsck_err(c, "snapshot with bad skiplist field:\n  %s",
-		      (bch2_bkey_val_to_text(&buf, c, k), buf.buf)))) {
-		u = bch2_bkey_make_mut_typed(trans, iter, &k, 0, snapshot);
-		ret = PTR_ERR_OR_ZERO(u);
-		if (ret)
-			goto err;
-
-		for (i = 0; i < ARRAY_SIZE(u->v.skip); i++)
-			u->v.skip[i] = cpu_to_le32(snapshot_skiplist_get(c, parent_id));
-
-		bubble_sort(u->v.skip, ARRAY_SIZE(u->v.skip), cmp_le32);
-		s = u->v;
-	}
-	ret = 0;
-err:
-fsck_err:
-	printbuf_exit(&buf);
-	return ret;
-}
-
-int bch2_check_snapshots(struct bch_fs *c)
-{
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	int ret;
-
-	/*
-	 * We iterate backwards as checking/fixing the depth field requires that
-	 * the parent's depth already be correct:
-	 */
-	ret = bch2_trans_run(c,
-		for_each_btree_key_reverse_commit(&trans, iter,
-			BTREE_ID_snapshots, POS_MAX,
-			BTREE_ITER_PREFETCH, k,
-			NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
-		check_snapshot(&trans, &iter, k)));
-	if (ret)
-		bch_err_fn(c, ret);
-	return ret;
-}
-
 static int check_subvol(struct btree_trans *trans,
 			struct btree_iter *iter,
 			struct bkey_s_c k)
@@ -900,7 +28,7 @@ static int check_subvol(struct btree_trans *trans,
 
 	subvol = bkey_s_c_to_subvolume(k);
 	snapid = le32_to_cpu(subvol.v->snapshot);
-	ret = snapshot_lookup(trans, snapid, &snapshot);
+	ret = bch2_snapshot_lookup(trans, snapid, &snapshot);
 
 	if (bch2_err_matches(ret, ENOENT))
 		bch_err(c, "subvolume %llu points to nonexistent snapshot %u",
@@ -968,462 +96,6 @@ int bch2_check_subvols(struct bch_fs *c)
 	return ret;
 }
 
-void bch2_fs_snapshots_exit(struct bch_fs *c)
-{
-	kfree(rcu_dereference_protected(c->snapshots, true));
-}
-
-int bch2_snapshots_read(struct bch_fs *c)
-{
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	int ret = 0;
-
-	ret = bch2_trans_run(c,
-		for_each_btree_key2(&trans, iter, BTREE_ID_snapshots,
-			   POS_MIN, 0, k,
-			bch2_mark_snapshot(&trans, BTREE_ID_snapshots, 0, bkey_s_c_null, k, 0) ?:
-			bch2_snapshot_set_equiv(&trans, k)));
-	if (ret)
-		bch_err_fn(c, ret);
-	return ret;
-}
-
-/*
- * Mark a snapshot as deleted, for future cleanup:
- */
-static int bch2_snapshot_node_set_deleted(struct btree_trans *trans, u32 id)
-{
-	struct btree_iter iter;
-	struct bkey_i_snapshot *s;
-	int ret = 0;
-
-	s = bch2_bkey_get_mut_typed(trans, &iter,
-				    BTREE_ID_snapshots, POS(0, id),
-				    0, snapshot);
-	ret = PTR_ERR_OR_ZERO(s);
-	if (unlikely(ret)) {
-		bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT),
-					trans->c, "missing snapshot %u", id);
-		return ret;
-	}
-
-	/* already deleted? */
-	if (BCH_SNAPSHOT_DELETED(&s->v))
-		goto err;
-
-	SET_BCH_SNAPSHOT_DELETED(&s->v, true);
-	SET_BCH_SNAPSHOT_SUBVOL(&s->v, false);
-	s->v.subvol = 0;
-err:
-	bch2_trans_iter_exit(trans, &iter);
-	return ret;
-}
-
-static int bch2_snapshot_node_delete(struct btree_trans *trans, u32 id)
-{
-	struct bch_fs *c = trans->c;
-	struct btree_iter iter, p_iter = (struct btree_iter) { NULL };
-	struct btree_iter tree_iter = (struct btree_iter) { NULL };
-	struct bkey_s_c_snapshot s;
-	u32 parent_id;
-	unsigned i;
-	int ret = 0;
-
-	s = bch2_bkey_get_iter_typed(trans, &iter, BTREE_ID_snapshots, POS(0, id),
-				     BTREE_ITER_INTENT, snapshot);
-	ret = bkey_err(s);
-	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), c,
-				"missing snapshot %u", id);
-
-	if (ret)
-		goto err;
-
-	BUG_ON(!BCH_SNAPSHOT_DELETED(s.v));
-	parent_id = le32_to_cpu(s.v->parent);
-
-	if (parent_id) {
-		struct bkey_i_snapshot *parent;
-
-		parent = bch2_bkey_get_mut_typed(trans, &p_iter,
-				     BTREE_ID_snapshots, POS(0, parent_id),
-				     0, snapshot);
-		ret = PTR_ERR_OR_ZERO(parent);
-		if (unlikely(ret)) {
-			bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), c,
-						"missing snapshot %u", parent_id);
-			goto err;
-		}
-
-		for (i = 0; i < 2; i++)
-			if (le32_to_cpu(parent->v.children[i]) == id)
-				break;
-
-		if (i == 2)
-			bch_err(c, "snapshot %u missing child pointer to %u",
-				parent_id, id);
-		else
-			parent->v.children[i] = 0;
-
-		if (le32_to_cpu(parent->v.children[0]) <
-		    le32_to_cpu(parent->v.children[1]))
-			swap(parent->v.children[0],
-			     parent->v.children[1]);
-	} else {
-		/*
-		 * We're deleting the root of a snapshot tree: update the
-		 * snapshot_tree entry to point to the new root, or delete it if
-		 * this is the last snapshot ID in this tree:
-		 */
-		struct bkey_i_snapshot_tree *s_t;
-
-		BUG_ON(s.v->children[1]);
-
-		s_t = bch2_bkey_get_mut_typed(trans, &tree_iter,
-				BTREE_ID_snapshot_trees, POS(0, le32_to_cpu(s.v->tree)),
-				0, snapshot_tree);
-		ret = PTR_ERR_OR_ZERO(s_t);
-		if (ret)
-			goto err;
-
-		if (s.v->children[0]) {
-			s_t->v.root_snapshot = s.v->children[0];
-		} else {
-			s_t->k.type = KEY_TYPE_deleted;
-			set_bkey_val_u64s(&s_t->k, 0);
-		}
-	}
-
-	ret = bch2_btree_delete_at(trans, &iter, 0);
-err:
-	bch2_trans_iter_exit(trans, &tree_iter);
-	bch2_trans_iter_exit(trans, &p_iter);
-	bch2_trans_iter_exit(trans, &iter);
-	return ret;
-}
-
-static int create_snapids(struct btree_trans *trans, u32 parent, u32 tree,
-			  u32 *new_snapids,
-			  u32 *snapshot_subvols,
-			  unsigned nr_snapids)
-{
-	struct bch_fs *c = trans->c;
-	struct btree_iter iter;
-	struct bkey_i_snapshot *n;
-	struct bkey_s_c k;
-	unsigned i, j;
-	u32 depth = bch2_snapshot_depth(c, parent);
-	int ret;
-
-	bch2_trans_iter_init(trans, &iter, BTREE_ID_snapshots,
-			     POS_MIN, BTREE_ITER_INTENT);
-	k = bch2_btree_iter_peek(&iter);
-	ret = bkey_err(k);
-	if (ret)
-		goto err;
-
-	for (i = 0; i < nr_snapids; i++) {
-		k = bch2_btree_iter_prev_slot(&iter);
-		ret = bkey_err(k);
-		if (ret)
-			goto err;
-
-		if (!k.k || !k.k->p.offset) {
-			ret = -BCH_ERR_ENOSPC_snapshot_create;
-			goto err;
-		}
-
-		n = bch2_bkey_alloc(trans, &iter, 0, snapshot);
-		ret = PTR_ERR_OR_ZERO(n);
-		if (ret)
-			goto err;
-
-		n->v.flags	= 0;
-		n->v.parent	= cpu_to_le32(parent);
-		n->v.subvol	= cpu_to_le32(snapshot_subvols[i]);
-		n->v.tree	= cpu_to_le32(tree);
-		n->v.depth	= cpu_to_le32(depth);
-
-		for (j = 0; j < ARRAY_SIZE(n->v.skip); j++)
-			n->v.skip[j] = cpu_to_le32(snapshot_skiplist_get(c, parent));
-
-		bubble_sort(n->v.skip, ARRAY_SIZE(n->v.skip), cmp_le32);
-		SET_BCH_SNAPSHOT_SUBVOL(&n->v, true);
-
-		ret = bch2_mark_snapshot(trans, BTREE_ID_snapshots, 0,
-					 bkey_s_c_null, bkey_i_to_s_c(&n->k_i), 0);
-		if (ret)
-			goto err;
-
-		new_snapids[i]	= iter.pos.offset;
-	}
-err:
-	bch2_trans_iter_exit(trans, &iter);
-	return ret;
-}
-
-/*
- * Create new snapshot IDs as children of an existing snapshot ID:
- */
-static int bch2_snapshot_node_create_children(struct btree_trans *trans, u32 parent,
-			      u32 *new_snapids,
-			      u32 *snapshot_subvols,
-			      unsigned nr_snapids)
-{
-	struct btree_iter iter;
-	struct bkey_i_snapshot *n_parent;
-	int ret = 0;
-
-	n_parent = bch2_bkey_get_mut_typed(trans, &iter,
-			BTREE_ID_snapshots, POS(0, parent),
-			0, snapshot);
-	ret = PTR_ERR_OR_ZERO(n_parent);
-	if (unlikely(ret)) {
-		if (bch2_err_matches(ret, ENOENT))
-			bch_err(trans->c, "snapshot %u not found", parent);
-		return ret;
-	}
-
-	if (n_parent->v.children[0] || n_parent->v.children[1]) {
-		bch_err(trans->c, "Trying to add child snapshot nodes to parent that already has children");
-		ret = -EINVAL;
-		goto err;
-	}
-
-	ret = create_snapids(trans, parent, le32_to_cpu(n_parent->v.tree),
-			     new_snapids, snapshot_subvols, nr_snapids);
-	if (ret)
-		goto err;
-
-	n_parent->v.children[0] = cpu_to_le32(new_snapids[0]);
-	n_parent->v.children[1] = cpu_to_le32(new_snapids[1]);
-	n_parent->v.subvol = 0;
-	SET_BCH_SNAPSHOT_SUBVOL(&n_parent->v, false);
-err:
-	bch2_trans_iter_exit(trans, &iter);
-	return ret;
-}
-
-/*
- * Create a snapshot node that is the root of a new tree:
- */
-static int bch2_snapshot_node_create_tree(struct btree_trans *trans,
-			      u32 *new_snapids,
-			      u32 *snapshot_subvols,
-			      unsigned nr_snapids)
-{
-	struct bkey_i_snapshot_tree *n_tree;
-	int ret;
-
-	n_tree = __snapshot_tree_create(trans);
-	ret =   PTR_ERR_OR_ZERO(n_tree) ?:
-		create_snapids(trans, 0, n_tree->k.p.offset,
-			     new_snapids, snapshot_subvols, nr_snapids);
-	if (ret)
-		return ret;
-
-	n_tree->v.master_subvol	= cpu_to_le32(snapshot_subvols[0]);
-	n_tree->v.root_snapshot	= cpu_to_le32(new_snapids[0]);
-	return 0;
-}
-
-int bch2_snapshot_node_create(struct btree_trans *trans, u32 parent,
-			      u32 *new_snapids,
-			      u32 *snapshot_subvols,
-			      unsigned nr_snapids)
-{
-	BUG_ON((parent == 0) != (nr_snapids == 1));
-	BUG_ON((parent != 0) != (nr_snapids == 2));
-
-	return parent
-		? bch2_snapshot_node_create_children(trans, parent,
-				new_snapids, snapshot_subvols, nr_snapids)
-		: bch2_snapshot_node_create_tree(trans,
-				new_snapids, snapshot_subvols, nr_snapids);
-
-}
-
-static int snapshot_delete_key(struct btree_trans *trans,
-			       struct btree_iter *iter,
-			       struct bkey_s_c k,
-			       snapshot_id_list *deleted,
-			       snapshot_id_list *equiv_seen,
-			       struct bpos *last_pos)
-{
-	struct bch_fs *c = trans->c;
-	u32 equiv = bch2_snapshot_equiv(c, k.k->p.snapshot);
-
-	if (!bkey_eq(k.k->p, *last_pos))
-		equiv_seen->nr = 0;
-	*last_pos = k.k->p;
-
-	if (snapshot_list_has_id(deleted, k.k->p.snapshot) ||
-	    snapshot_list_has_id(equiv_seen, equiv)) {
-		return bch2_btree_delete_at(trans, iter,
-					    BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
-	} else {
-		return snapshot_list_add(c, equiv_seen, equiv);
-	}
-}
-
-static int bch2_delete_redundant_snapshot(struct btree_trans *trans, struct btree_iter *iter,
-					  struct bkey_s_c k)
-{
-	struct bkey_s_c_snapshot snap;
-	u32 children[2];
-	int ret;
-
-	if (k.k->type != KEY_TYPE_snapshot)
-		return 0;
-
-	snap = bkey_s_c_to_snapshot(k);
-	if (BCH_SNAPSHOT_DELETED(snap.v) ||
-	    BCH_SNAPSHOT_SUBVOL(snap.v))
-		return 0;
-
-	children[0] = le32_to_cpu(snap.v->children[0]);
-	children[1] = le32_to_cpu(snap.v->children[1]);
-
-	ret   = snapshot_live(trans, children[0]) ?:
-		snapshot_live(trans, children[1]);
-	if (ret < 0)
-		return ret;
-
-	if (!ret)
-		return bch2_snapshot_node_set_deleted(trans, k.k->p.offset);
-	return 0;
-}
-
-int bch2_delete_dead_snapshots(struct bch_fs *c)
-{
-	struct btree_trans trans;
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	struct bkey_s_c_snapshot snap;
-	snapshot_id_list deleted = { 0 };
-	u32 i, id;
-	int ret = 0;
-
-	if (!test_bit(BCH_FS_STARTED, &c->flags)) {
-		ret = bch2_fs_read_write_early(c);
-		if (ret) {
-			bch_err(c, "error deleleting dead snapshots: error going rw: %s", bch2_err_str(ret));
-			return ret;
-		}
-	}
-
-	bch2_trans_init(&trans, c, 0, 0);
-
-	/*
-	 * For every snapshot node: If we have no live children and it's not
-	 * pointed to by a subvolume, delete it:
-	 */
-	ret = for_each_btree_key_commit(&trans, iter, BTREE_ID_snapshots,
-			POS_MIN, 0, k,
-			NULL, NULL, 0,
-		bch2_delete_redundant_snapshot(&trans, &iter, k));
-	if (ret) {
-		bch_err(c, "error deleting redundant snapshots: %s", bch2_err_str(ret));
-		goto err;
-	}
-
-	for_each_btree_key2(&trans, iter, BTREE_ID_snapshots,
-			   POS_MIN, 0, k,
-		bch2_snapshot_set_equiv(&trans, k));
-	if (ret) {
-		bch_err(c, "error in bch2_snapshots_set_equiv: %s", bch2_err_str(ret));
-		goto err;
-	}
-
-	for_each_btree_key(&trans, iter, BTREE_ID_snapshots,
-			   POS_MIN, 0, k, ret) {
-		if (k.k->type != KEY_TYPE_snapshot)
-			continue;
-
-		snap = bkey_s_c_to_snapshot(k);
-		if (BCH_SNAPSHOT_DELETED(snap.v)) {
-			ret = snapshot_list_add(c, &deleted, k.k->p.offset);
-			if (ret)
-				break;
-		}
-	}
-	bch2_trans_iter_exit(&trans, &iter);
-
-	if (ret) {
-		bch_err(c, "error walking snapshots: %s", bch2_err_str(ret));
-		goto err;
-	}
-
-	for (id = 0; id < BTREE_ID_NR; id++) {
-		struct bpos last_pos = POS_MIN;
-		snapshot_id_list equiv_seen = { 0 };
-
-		if (!btree_type_has_snapshots(id))
-			continue;
-
-		ret = for_each_btree_key_commit(&trans, iter,
-				id, POS_MIN,
-				BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS, k,
-				NULL, NULL, BTREE_INSERT_NOFAIL,
-			snapshot_delete_key(&trans, &iter, k, &deleted, &equiv_seen, &last_pos));
-
-		darray_exit(&equiv_seen);
-
-		if (ret) {
-			bch_err(c, "error deleting snapshot keys: %s", bch2_err_str(ret));
-			goto err;
-		}
-	}
-
-	for (i = 0; i < deleted.nr; i++) {
-		ret = commit_do(&trans, NULL, NULL, 0,
-			bch2_snapshot_node_delete(&trans, deleted.data[i]));
-		if (ret) {
-			bch_err(c, "error deleting snapshot %u: %s",
-				deleted.data[i], bch2_err_str(ret));
-			goto err;
-		}
-	}
-
-	clear_bit(BCH_FS_HAVE_DELETED_SNAPSHOTS, &c->flags);
-err:
-	darray_exit(&deleted);
-	bch2_trans_exit(&trans);
-	if (ret)
-		bch_err_fn(c, ret);
-	return ret;
-}
-
-static void bch2_delete_dead_snapshots_work(struct work_struct *work)
-{
-	struct bch_fs *c = container_of(work, struct bch_fs, snapshot_delete_work);
-
-	if (test_bit(BCH_FS_HAVE_DELETED_SNAPSHOTS, &c->flags))
-		bch2_delete_dead_snapshots(c);
-	bch2_write_ref_put(c, BCH_WRITE_REF_delete_dead_snapshots);
-}
-
-void bch2_delete_dead_snapshots_async(struct bch_fs *c)
-{
-	if (bch2_write_ref_tryget(c, BCH_WRITE_REF_delete_dead_snapshots) &&
-	    !queue_work(c->write_ref_wq, &c->snapshot_delete_work))
-		bch2_write_ref_put(c, BCH_WRITE_REF_delete_dead_snapshots);
-}
-
-static int bch2_delete_dead_snapshots_hook(struct btree_trans *trans,
-					   struct btree_trans_commit_hook *h)
-{
-	struct bch_fs *c = trans->c;
-
-	set_bit(BCH_FS_HAVE_DELETED_SNAPSHOTS, &c->flags);
-
-	if (c->curr_recovery_pass <= BCH_RECOVERY_PASS_delete_dead_snapshots)
-		return 0;
-
-	bch2_delete_dead_snapshots_async(c);
-	return 0;
-}
-
 /* Subvolumes: */
 
 int bch2_subvolume_invalid(const struct bch_fs *c, struct bkey_s_c k,
@@ -1478,26 +150,27 @@ int bch2_snapshot_get_subvol(struct btree_trans *trans, u32 snapshot,
 {
 	struct bch_snapshot snap;
 
-	return  snapshot_lookup(trans, snapshot, &snap) ?:
+	return  bch2_snapshot_lookup(trans, snapshot, &snap) ?:
 		bch2_subvolume_get(trans, le32_to_cpu(snap.subvol), true, 0, subvol);
 }
 
-int bch2_subvolume_get_snapshot(struct btree_trans *trans, u32 subvol,
+int bch2_subvolume_get_snapshot(struct btree_trans *trans, u32 subvolid,
 				u32 *snapid)
 {
 	struct btree_iter iter;
-	struct bkey_s_c k;
+	struct bkey_s_c_subvolume subvol;
 	int ret;
 
-	k = bch2_bkey_get_iter(trans, &iter, BTREE_ID_subvolumes, POS(0, subvol),
-			       BTREE_ITER_CACHED|
-			       BTREE_ITER_WITH_UPDATES);
-	ret = bkey_err(k) ?: k.k->type == KEY_TYPE_subvolume ? 0 : -BCH_ERR_ENOENT_subvolume;
+	subvol = bch2_bkey_get_iter_typed(trans, &iter,
+					  BTREE_ID_subvolumes, POS(0, subvolid),
+					  BTREE_ITER_CACHED|BTREE_ITER_WITH_UPDATES,
+					  subvolume);
+	ret = bkey_err(subvol);
+	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), trans->c,
+				"missing subvolume %u", subvolid);
 
 	if (likely(!ret))
-		*snapid = le32_to_cpu(bkey_s_c_to_subvolume(k).v->snapshot);
-	else if (bch2_err_matches(ret, ENOENT))
-		bch2_fs_inconsistent(trans->c, "missing subvolume %u", subvol);
+		*snapid = le32_to_cpu(subvol.v->snapshot);
 	bch2_trans_iter_exit(trans, &iter);
 	return ret;
 }
@@ -1527,7 +200,12 @@ static int bch2_subvolume_reparent(struct btree_trans *trans,
 }
 
 /*
- * Scan for subvolumes with parent @subvolid_to_delete, reparent:
+ * Separate from the snapshot tree in the snapshots btree, we record the tree
+ * structure of how snapshot subvolumes were created - the parent subvolume of
+ * each snapshot subvolume.
+ *
+ * When a subvolume is deleted, we scan for child subvolumes and reparant them,
+ * to avoid dangling references:
  */
 static int bch2_subvolumes_reparent(struct btree_trans *trans, u32 subvolid_to_delete)
 {