Update bcachefs sources to 386f00b639 bcachefs: Snapshot creation, deletion

1 files changed, 981 insertions, 0 deletions

diff --git a/libbcachefs/subvolume.c b/libbcachefs/subvolume.c
new file mode 100644
index 00000000..ff3b4d2d
--- /dev/null
+++ b/libbcachefs/subvolume.c
@@ -0,0 +1,981 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "bcachefs.h"
+#include "btree_key_cache.h"
+#include "btree_update.h"
+#include "error.h"
+#include "subvolume.h"
+
+/* Snapshot tree: */
+
+static void bch2_delete_dead_snapshots_work(struct work_struct *);
+static void bch2_delete_dead_snapshots(struct bch_fs *);
+
+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);
+
+	pr_buf(out, "is_subvol %llu deleted %llu parent %u children %u %u subvol %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));
+}
+
+const char *bch2_snapshot_invalid(const struct bch_fs *c, struct bkey_s_c k)
+{
+	struct bkey_s_c_snapshot s;
+	u32 i, id;
+
+	if (bkey_cmp(k.k->p, POS(0, U32_MAX)) > 0 ||
+	    bkey_cmp(k.k->p, POS(0, 1)) < 0)
+		return "bad pos";
+
+	if (bkey_val_bytes(k.k) != sizeof(struct bch_snapshot))
+		return "bad val size";
+
+	s = bkey_s_c_to_snapshot(k);
+
+	id = le32_to_cpu(s.v->parent);
+	if (id && id <= k.k->p.offset)
+		return "bad parent node";
+
+	if (le32_to_cpu(s.v->children[0]) < le32_to_cpu(s.v->children[1]))
+		return "children not normalized";
+
+	if (s.v->children[0] &&
+	    s.v->children[0] == s.v->children[1])
+		return "duplicate child nodes";
+
+	for (i = 0; i < 2; i++) {
+		id = le32_to_cpu(s.v->children[i]);
+
+		if (id >= k.k->p.offset)
+			return "bad child node";
+	}
+
+	return NULL;
+}
+
+int bch2_mark_snapshot(struct bch_fs *c,
+		       struct bkey_s_c old, struct bkey_s_c new,
+		       u64 journal_seq, unsigned flags)
+{
+	struct snapshot_t *t;
+
+	t = genradix_ptr_alloc(&c->snapshots,
+			       U32_MAX - new.k->p.offset,
+			       GFP_KERNEL);
+	if (!t)
+		return -ENOMEM;
+
+	if (new.k->type == KEY_TYPE_snapshot) {
+		struct bkey_s_c_snapshot s = bkey_s_c_to_snapshot(new);
+
+		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;
+	} else {
+		t->parent	= 0;
+		t->children[0]	= 0;
+		t->children[1]	= 0;
+		t->subvol	= 0;
+	}
+
+	return 0;
+}
+
+static int subvol_lookup(struct btree_trans *trans, unsigned id, struct bch_subvolume *s)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_subvolumes, POS(0, id), 0);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k) ?: k.k->type == KEY_TYPE_subvolume ? 0 : -ENOENT;
+
+	if (!ret)
+		*s = *bkey_s_c_to_subvolume(k).v;
+
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static int snapshot_lookup(struct btree_trans *trans, u32 id,
+			   struct bch_snapshot *s)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_snapshots, POS(0, id),
+			     BTREE_ITER_WITH_UPDATES);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k) ?: k.k->type == KEY_TYPE_snapshot ? 0 : -ENOENT;
+
+	if (!ret)
+		*s = *bkey_s_c_to_snapshot(k).v;
+
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static int snapshot_live(struct btree_trans *trans, u32 id)
+{
+	struct bch_snapshot v;
+	int ret;
+
+	if (!id)
+		return 0;
+
+	ret = lockrestart_do(trans, snapshot_lookup(trans, id, &v));
+	if (ret == -ENOENT)
+		bch_err(trans->c, "snapshot node %u not found", id);
+	if (ret)
+		return ret;
+
+	return !BCH_SNAPSHOT_DELETED(&v);
+}
+
+static int bch2_snapshots_set_equiv(struct btree_trans *trans)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bkey_s_c_snapshot snap;
+	unsigned i;
+	int ret;
+
+	for_each_btree_key(trans, iter, BTREE_ID_snapshots,
+			   POS_MIN, 0, k, ret) {
+		u32 id = k.k->p.offset, child[2];
+		unsigned nr_live = 0, live_idx;
+
+		if (k.k->type != KEY_TYPE_snapshot)
+			continue;
+
+		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++) {
+			ret = snapshot_live(trans, child[i]);
+			if (ret < 0)
+				break;
+
+			if (ret)
+				live_idx = i;
+			nr_live += ret;
+		}
+
+		snapshot_t(c, id)->equiv = nr_live == 1
+			? snapshot_t(c, child[live_idx])->equiv
+			: id;
+	}
+	bch2_trans_iter_exit(trans, &iter);
+
+	if (ret)
+		bch_err(c, "error walking snapshots: %i", ret);
+
+	return ret;
+}
+
+/* fsck: */
+static int bch2_snapshot_check(struct btree_trans *trans,
+			       struct bkey_s_c_snapshot s)
+{
+	struct bch_subvolume subvol;
+	struct bch_snapshot v;
+	u32 i, id;
+	int ret;
+
+	id = le32_to_cpu(s.v->subvol);
+	ret = lockrestart_do(trans, subvol_lookup(trans, id, &subvol));
+	if (ret == -ENOENT)
+		bch_err(trans->c, "snapshot node %llu has nonexistent subvolume %u",
+			s.k->p.offset, id);
+	if (ret)
+		return ret;
+
+	if (BCH_SNAPSHOT_SUBVOL(s.v) != (le32_to_cpu(subvol.snapshot) == s.k->p.offset)) {
+		bch_err(trans->c, "snapshot node %llu has wrong BCH_SNAPSHOT_SUBVOL",
+			s.k->p.offset);
+		return -EINVAL;
+	}
+
+	id = le32_to_cpu(s.v->parent);
+	if (id) {
+		ret = lockrestart_do(trans, snapshot_lookup(trans, id, &v));
+		if (ret == -ENOENT)
+			bch_err(trans->c, "snapshot node %llu has nonexistent parent %u",
+				s.k->p.offset, id);
+		if (ret)
+			return ret;
+
+		if (le32_to_cpu(v.children[0]) != s.k->p.offset &&
+		    le32_to_cpu(v.children[1]) != s.k->p.offset) {
+			bch_err(trans->c, "snapshot parent %u missing pointer to child %llu",
+				id, s.k->p.offset);
+			return -EINVAL;
+		}
+	}
+
+	for (i = 0; i < 2 && s.v->children[i]; i++) {
+		id = le32_to_cpu(s.v->children[i]);
+
+		ret = lockrestart_do(trans, snapshot_lookup(trans, id, &v));
+		if (ret == -ENOENT)
+			bch_err(trans->c, "snapshot node %llu has nonexistent child %u",
+				s.k->p.offset, id);
+		if (ret)
+			return ret;
+
+		if (le32_to_cpu(v.parent) != s.k->p.offset) {
+			bch_err(trans->c, "snapshot child %u has wrong parent (got %u should be %llu)",
+				id, le32_to_cpu(v.parent), s.k->p.offset);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+int bch2_fs_snapshots_check(struct bch_fs *c)
+{
+	struct btree_trans trans;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bch_snapshot s;
+	unsigned id;
+	int ret;
+
+	bch2_trans_init(&trans, c, 0, 0);
+
+	for_each_btree_key(&trans, iter, BTREE_ID_snapshots,
+			   POS_MIN, 0, k, ret) {
+		if (k.k->type != KEY_TYPE_snapshot)
+			continue;
+
+		ret = bch2_snapshot_check(&trans, bkey_s_c_to_snapshot(k));
+		if (ret)
+			break;
+	}
+	bch2_trans_iter_exit(&trans, &iter);
+
+	if (ret) {
+		bch_err(c, "error %i checking snapshots", ret);
+		goto err;
+	}
+
+	for_each_btree_key(&trans, iter, BTREE_ID_subvolumes,
+			   POS_MIN, 0, k, ret) {
+		if (k.k->type != KEY_TYPE_subvolume)
+			continue;
+again_2:
+		id = le32_to_cpu(bkey_s_c_to_subvolume(k).v->snapshot);
+		ret = snapshot_lookup(&trans, id, &s);
+
+		if (ret == -EINTR) {
+			k = bch2_btree_iter_peek(&iter);
+			goto again_2;
+		} else if (ret == -ENOENT)
+			bch_err(c, "subvolume %llu points to nonexistent snapshot %u",
+				k.k->p.offset, id);
+		else if (ret)
+			break;
+	}
+	bch2_trans_iter_exit(&trans, &iter);
+err:
+	bch2_trans_exit(&trans);
+	return ret;
+}
+
+void bch2_fs_snapshots_exit(struct bch_fs *c)
+{
+	genradix_free(&c->snapshots);
+}
+
+int bch2_fs_snapshots_start(struct bch_fs *c)
+{
+	struct btree_trans trans;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	bool have_deleted = false;
+	int ret = 0;
+
+	bch2_trans_init(&trans, c, 0, 0);
+
+	for_each_btree_key(&trans, iter, BTREE_ID_snapshots,
+			   POS_MIN, 0, k, ret) {
+	       if (bkey_cmp(k.k->p, POS(0, U32_MAX)) > 0)
+		       break;
+
+		if (k.k->type != KEY_TYPE_snapshot) {
+			bch_err(c, "found wrong key type %u in snapshot node table",
+				k.k->type);
+			continue;
+		}
+
+		if (BCH_SNAPSHOT_DELETED(bkey_s_c_to_snapshot(k).v))
+			have_deleted = true;
+
+		ret = bch2_mark_snapshot(c, bkey_s_c_null, k, 0, 0);
+		if (ret)
+			break;
+	}
+	bch2_trans_iter_exit(&trans, &iter);
+
+	if (ret)
+		goto err;
+
+	ret = bch2_snapshots_set_equiv(&trans);
+	if (ret)
+		goto err;
+err:
+	bch2_trans_exit(&trans);
+
+	if (!ret && have_deleted) {
+		bch_info(c, "restarting deletion of dead snapshots");
+		if (c->opts.fsck) {
+			bch2_delete_dead_snapshots_work(&c->snapshot_delete_work);
+		} else {
+			bch2_delete_dead_snapshots(c);
+		}
+	}
+
+	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_s_c k;
+	struct bkey_i_snapshot *s;
+	int ret = 0;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_snapshots, POS(0, id),
+			     BTREE_ITER_INTENT);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k);
+	if (ret)
+		goto err;
+
+	if (k.k->type != KEY_TYPE_snapshot) {
+		bch2_fs_inconsistent(trans->c, "missing snapshot %u", id);
+		ret = -ENOENT;
+		goto err;
+	}
+
+	/* already deleted? */
+	if (BCH_SNAPSHOT_DELETED(bkey_s_c_to_snapshot(k).v))
+		goto err;
+
+	s = bch2_trans_kmalloc(trans, sizeof(*s));
+	ret = PTR_ERR_OR_ZERO(s);
+	if (ret)
+		goto err;
+
+	bkey_reassemble(&s->k_i, k);
+
+	SET_BCH_SNAPSHOT_DELETED(&s->v, true);
+	ret = bch2_trans_update(trans, &iter, &s->k_i, 0);
+	if (ret)
+		goto err;
+err:
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static int bch2_snapshot_node_delete(struct btree_trans *trans, u32 id)
+{
+	struct btree_iter iter, p_iter = (struct btree_iter) { NULL };
+	struct bkey_s_c k;
+	struct bkey_s_c_snapshot s;
+	struct bkey_i_snapshot *parent;
+	u32 parent_id;
+	unsigned i;
+	int ret = 0;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_snapshots, POS(0, id),
+			     BTREE_ITER_INTENT);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k);
+	if (ret)
+		goto err;
+
+	if (k.k->type != KEY_TYPE_snapshot) {
+		bch2_fs_inconsistent(trans->c, "missing snapshot %u", id);
+		ret = -ENOENT;
+		goto err;
+	}
+
+	s = bkey_s_c_to_snapshot(k);
+
+	BUG_ON(!BCH_SNAPSHOT_DELETED(s.v));
+	parent_id = le32_to_cpu(s.v->parent);
+
+	if (parent_id) {
+		bch2_trans_iter_init(trans, &p_iter, BTREE_ID_snapshots,
+				     POS(0, parent_id),
+				     BTREE_ITER_INTENT);
+		k = bch2_btree_iter_peek_slot(&p_iter);
+		ret = bkey_err(k);
+		if (ret)
+			goto err;
+
+		if (k.k->type != KEY_TYPE_snapshot) {
+			bch2_fs_inconsistent(trans->c, "missing snapshot %u", parent_id);
+			ret = -ENOENT;
+			goto err;
+		}
+
+		parent = bch2_trans_kmalloc(trans, sizeof(*parent));
+		ret = PTR_ERR_OR_ZERO(parent);
+		if (ret)
+			goto err;
+
+		bkey_reassemble(&parent->k_i, k);
+
+		for (i = 0; i < 2; i++)
+			if (le32_to_cpu(parent->v.children[i]) == id)
+				break;
+
+		if (i == 2)
+			bch_err(trans->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]);
+
+		ret = bch2_trans_update(trans, &p_iter, &parent->k_i, 0);
+		if (ret)
+			goto err;
+	}
+
+	ret = bch2_btree_delete_at(trans, &iter, 0);
+err:
+	bch2_trans_iter_exit(trans, &p_iter);
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static int bch2_snapshot_node_create(struct btree_trans *trans, u32 parent,
+				     u32 *new_snapids,
+				     u32 *snapshot_subvols,
+				     unsigned nr_snapids)
+{
+	struct btree_iter iter;
+	struct bkey_i_snapshot *n;
+	struct bkey_s_c k;
+	unsigned i;
+	int ret = 0;
+
+	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 = -ENOSPC;
+			goto err;
+		}
+
+		n = bch2_trans_kmalloc(trans, sizeof(*n));
+		ret = PTR_ERR_OR_ZERO(n);
+		if (ret)
+			return ret;
+
+		bkey_snapshot_init(&n->k_i);
+		n->k.p		= iter.pos;
+		n->v.flags	= 0;
+		n->v.parent	= cpu_to_le32(parent);
+		n->v.subvol	= cpu_to_le32(snapshot_subvols[i]);
+		n->v.pad	= 0;
+		SET_BCH_SNAPSHOT_SUBVOL(&n->v, true);
+
+		bch2_trans_update(trans, &iter, &n->k_i, 0);
+
+		ret = bch2_mark_snapshot(trans->c, bkey_s_c_null, bkey_i_to_s_c(&n->k_i), 0, 0);
+		if (ret)
+			break;
+
+		new_snapids[i]	= iter.pos.offset;
+	}
+
+	if (parent) {
+		bch2_btree_iter_set_pos(&iter, POS(0, parent));
+		k = bch2_btree_iter_peek(&iter);
+		ret = bkey_err(k);
+		if (ret)
+			goto err;
+
+		if (k.k->type != KEY_TYPE_snapshot) {
+			bch_err(trans->c, "snapshot %u not found", parent);
+			ret = -ENOENT;
+			goto err;
+		}
+
+		n = bch2_trans_kmalloc(trans, sizeof(*n));
+		ret = PTR_ERR_OR_ZERO(n);
+		if (ret)
+			return ret;
+
+		bkey_reassemble(&n->k_i, k);
+
+		if (n->v.children[0] || n->v.children[1]) {
+			bch_err(trans->c, "Trying to add child snapshot nodes to parent that already has children");
+			ret = -EINVAL;
+			goto err;
+		}
+
+		n->v.children[0] = cpu_to_le32(new_snapids[0]);
+		n->v.children[1] = cpu_to_le32(new_snapids[1]);
+		SET_BCH_SNAPSHOT_SUBVOL(&n->v, false);
+		bch2_trans_update(trans, &iter, &n->k_i, 0);
+	}
+err:
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+/* List of snapshot IDs that are being deleted: */
+struct snapshot_id_list {
+	u32		nr;
+	u32		size;
+	u32		*d;
+};
+
+static bool snapshot_list_has_id(struct snapshot_id_list *s, u32 id)
+{
+	unsigned i;
+
+	for (i = 0; i < s->nr; i++)
+		if (id == s->d[i])
+			return true;
+	return false;
+}
+
+static int snapshot_id_add(struct snapshot_id_list *s, u32 id)
+{
+	BUG_ON(snapshot_list_has_id(s, id));
+
+	if (s->nr == s->size) {
+		size_t new_size = max(8U, s->size * 2);
+		void *n = krealloc(s->d,
+				   new_size * sizeof(s->d[0]),
+				   GFP_KERNEL);
+		if (!n) {
+			pr_err("error allocating snapshot ID list");
+			return -ENOMEM;
+		}
+
+		s->d	= n;
+		s->size = new_size;
+	};
+
+	s->d[s->nr++] = id;
+	return 0;
+}
+
+static int bch2_snapshot_delete_keys_btree(struct btree_trans *trans,
+					   struct snapshot_id_list *deleted,
+					   enum btree_id btree_id)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct snapshot_id_list equiv_seen = { 0 };
+	struct bpos last_pos = POS_MIN;
+	int ret = 0;
+
+	/*
+	 * XXX: We should also delete whiteouts that no longer overwrite
+	 * anything
+	 */
+
+	bch2_trans_iter_init(trans, &iter, btree_id, POS_MIN,
+			     BTREE_ITER_INTENT|
+			     BTREE_ITER_PREFETCH|
+			     BTREE_ITER_NOT_EXTENTS|
+			     BTREE_ITER_ALL_SNAPSHOTS);
+
+	while ((bch2_trans_begin(trans),
+		(k = bch2_btree_iter_peek(&iter)).k) &&
+	       !(ret = bkey_err(k))) {
+		u32 equiv = snapshot_t(c, k.k->p.snapshot)->equiv;
+
+		if (bkey_cmp(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)) {
+			if (btree_id == BTREE_ID_inodes &&
+			    bch2_btree_key_cache_flush(trans, btree_id, iter.pos))
+				continue;
+
+			ret = __bch2_trans_do(trans, NULL, NULL,
+					      BTREE_INSERT_NOFAIL,
+				bch2_btree_iter_traverse(&iter) ?:
+				bch2_btree_delete_at(trans, &iter,
+					BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE));
+			if (ret)
+				break;
+		} else {
+			ret = snapshot_id_add(&equiv_seen, equiv);
+			if (ret)
+				break;
+		}
+
+		bch2_btree_iter_advance(&iter);
+	}
+	bch2_trans_iter_exit(trans, &iter);
+
+	kfree(equiv_seen.d);
+
+	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);
+	struct btree_trans trans;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bkey_s_c_snapshot snap;
+	struct snapshot_id_list deleted = { 0 };
+	u32 i, id, children[2];
+	int ret = 0;
+
+	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:
+	 */
+	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) ||
+		    BCH_SNAPSHOT_SUBVOL(snap.v))
+			continue;
+
+		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)
+			break;
+		if (ret)
+			continue;
+
+		ret = __bch2_trans_do(&trans, NULL, NULL, 0,
+			bch2_snapshot_node_set_deleted(&trans, iter.pos.offset));
+		if (ret) {
+			bch_err(c, "error deleting snapshot %llu: %i", iter.pos.offset, ret);
+			break;
+		}
+	}
+	bch2_trans_iter_exit(&trans, &iter);
+
+	if (ret) {
+		bch_err(c, "error walking snapshots: %i", ret);
+		goto err;
+	}
+
+	ret = bch2_snapshots_set_equiv(&trans);
+	if (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_id_add(&deleted, k.k->p.offset);
+			if (ret)
+				break;
+		}
+	}
+	bch2_trans_iter_exit(&trans, &iter);
+
+	if (ret) {
+		bch_err(c, "error walking snapshots: %i", ret);
+		goto err;
+	}
+
+	for (id = 0; id < BTREE_ID_NR; id++) {
+		if (!btree_type_has_snapshots(id))
+			continue;
+
+		ret = bch2_snapshot_delete_keys_btree(&trans, &deleted, id);
+		if (ret) {
+			bch_err(c, "error deleting snapshot keys: %i", ret);
+			goto err;
+		}
+	}
+
+	for (i = 0; i < deleted.nr; i++) {
+		ret = __bch2_trans_do(&trans, NULL, NULL, 0,
+			bch2_snapshot_node_delete(&trans, deleted.d[i]));
+		if (ret) {
+			bch_err(c, "error deleting snapshot %u: %i",
+				deleted.d[i], ret);
+			goto err;
+		}
+	}
+err:
+	kfree(deleted.d);
+	bch2_trans_exit(&trans);
+	percpu_ref_put(&c->writes);
+}
+
+static void bch2_delete_dead_snapshots(struct bch_fs *c)
+{
+	if (unlikely(!percpu_ref_tryget(&c->writes)))
+		return;
+
+	if (!queue_work(system_long_wq, &c->snapshot_delete_work))
+		percpu_ref_put(&c->writes);
+}
+
+static int bch2_delete_dead_snapshots_hook(struct btree_trans *trans,
+					   struct btree_trans_commit_hook *h)
+{
+	bch2_delete_dead_snapshots(trans->c);
+	return 0;
+}
+
+/* Subvolumes: */
+
+const char *bch2_subvolume_invalid(const struct bch_fs *c, struct bkey_s_c k)
+{
+	if (bkey_cmp(k.k->p, SUBVOL_POS_MIN) < 0)
+		return "invalid pos";
+
+	if (bkey_cmp(k.k->p, SUBVOL_POS_MAX) > 0)
+		return "invalid pos";
+
+	if (bkey_val_bytes(k.k) != sizeof(struct bch_subvolume))
+		return "bad val size";
+
+	return NULL;
+}
+
+void bch2_subvolume_to_text(struct printbuf *out, struct bch_fs *c,
+			    struct bkey_s_c k)
+{
+	struct bkey_s_c_subvolume s = bkey_s_c_to_subvolume(k);
+
+	pr_buf(out, "root %llu snapshot id %u",
+	       le64_to_cpu(s.v->inode),
+	       le32_to_cpu(s.v->snapshot));
+}
+
+int bch2_subvolume_get_snapshot(struct btree_trans *trans, u32 subvol,
+				u32 *snapid)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_subvolumes,
+			     POS(0, subvol),
+			     BTREE_ITER_CACHED|
+			     BTREE_ITER_WITH_UPDATES);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k);
+	if (ret)
+		goto err;
+
+	if (k.k->type != KEY_TYPE_subvolume) {
+		bch2_fs_inconsistent(trans->c, "missing subvolume %u", subvol);
+		ret = -EIO;
+		goto err;
+	}
+
+	*snapid = le32_to_cpu(bkey_s_c_to_subvolume(k).v->snapshot);
+err:
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+/* XXX: mark snapshot id for deletion, walk btree and delete: */
+int bch2_subvolume_delete(struct btree_trans *trans, u32 subvolid,
+			  int deleting_snapshot)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bkey_s_c_subvolume subvol;
+	struct btree_trans_commit_hook *h;
+	struct bkey_i *delete;
+	u32 snapid;
+	int ret = 0;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_subvolumes,
+			     POS(0, subvolid),
+			     BTREE_ITER_CACHED|
+			     BTREE_ITER_INTENT);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k);
+	if (ret)
+		goto err;
+
+	if (k.k->type != KEY_TYPE_subvolume) {
+		bch2_fs_inconsistent(trans->c, "missing subvolume %u", subvolid);
+		ret = -EIO;
+		goto err;
+	}
+
+	subvol = bkey_s_c_to_subvolume(k);
+	snapid = le32_to_cpu(subvol.v->snapshot);
+
+	if (deleting_snapshot >= 0 &&
+	    deleting_snapshot != BCH_SUBVOLUME_SNAP(subvol.v)) {
+		ret = -ENOENT;
+		goto err;
+	}
+
+	delete = bch2_trans_kmalloc(trans, sizeof(*delete));
+	ret = PTR_ERR_OR_ZERO(delete);
+	if (ret)
+		goto err;
+
+	bkey_init(&delete->k);
+	delete->k.p = iter.pos;
+	ret = bch2_trans_update(trans, &iter, delete, 0);
+	if (ret)
+		goto err;
+
+	ret = bch2_snapshot_node_set_deleted(trans, snapid);
+
+	h = bch2_trans_kmalloc(trans, sizeof(*h));
+	ret = PTR_ERR_OR_ZERO(h);
+	if (ret)
+		goto err;
+
+	h->fn = bch2_delete_dead_snapshots_hook;
+	bch2_trans_commit_hook(trans, h);
+err:
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+int bch2_subvolume_create(struct btree_trans *trans, u64 inode,
+			  u32 src_subvolid,
+			  u32 *new_subvolid,
+			  u32 *new_snapshotid,
+			  bool ro)
+{
+	struct btree_iter dst_iter, src_iter = (struct btree_iter) { NULL };
+	struct bkey_i_subvolume *new_subvol = NULL;
+	struct bkey_i_subvolume *src_subvol = NULL;
+	struct bkey_s_c k;
+	u32 parent = 0, new_nodes[2], snapshot_subvols[2];
+	int ret = 0;
+
+	for_each_btree_key(trans, dst_iter, BTREE_ID_subvolumes, SUBVOL_POS_MIN,
+			   BTREE_ITER_SLOTS|BTREE_ITER_INTENT, k, ret) {
+		if (bkey_cmp(k.k->p, SUBVOL_POS_MAX) > 0)
+			break;
+		if (bkey_deleted(k.k))
+			goto found_slot;
+	}
+
+	if (!ret)
+		ret = -ENOSPC;
+	goto err;
+found_slot:
+	snapshot_subvols[0] = dst_iter.pos.offset;
+	snapshot_subvols[1] = src_subvolid;
+
+	if (src_subvolid) {
+		/* Creating a snapshot: */
+		src_subvol = bch2_trans_kmalloc(trans, sizeof(*src_subvol));
+		ret = PTR_ERR_OR_ZERO(src_subvol);
+		if (ret)
+			goto err;
+
+		bch2_trans_iter_init(trans, &src_iter, BTREE_ID_subvolumes,
+				     POS(0, src_subvolid),
+				     BTREE_ITER_CACHED|
+				     BTREE_ITER_INTENT);
+		k = bch2_btree_iter_peek_slot(&src_iter);
+		ret = bkey_err(k);
+		if (ret)
+			goto err;
+
+		if (k.k->type != KEY_TYPE_subvolume) {
+			bch_err(trans->c, "subvolume %u not found", src_subvolid);
+			ret = -ENOENT;
+			goto err;
+		}
+
+		bkey_reassemble(&src_subvol->k_i, k);
+		parent = le32_to_cpu(src_subvol->v.snapshot);
+	}
+
+	ret = bch2_snapshot_node_create(trans, parent, new_nodes,
+					snapshot_subvols,
+					src_subvolid ? 2 : 1);
+	if (ret)
+		goto err;
+
+	if (src_subvolid) {
+		src_subvol->v.snapshot = cpu_to_le32(new_nodes[1]);
+		bch2_trans_update(trans, &src_iter, &src_subvol->k_i, 0);
+	}
+
+	new_subvol = bch2_trans_kmalloc(trans, sizeof(*new_subvol));
+	ret = PTR_ERR_OR_ZERO(new_subvol);
+	if (ret)
+		goto err;
+
+	bkey_subvolume_init(&new_subvol->k_i);
+	new_subvol->v.flags	= 0;
+	new_subvol->v.snapshot	= cpu_to_le32(new_nodes[0]);
+	new_subvol->v.inode	= cpu_to_le64(inode);
+	SET_BCH_SUBVOLUME_RO(&new_subvol->v, ro);
+	SET_BCH_SUBVOLUME_SNAP(&new_subvol->v, src_subvolid != 0);
+	new_subvol->k.p		= dst_iter.pos;
+	bch2_trans_update(trans, &dst_iter, &new_subvol->k_i, 0);
+
+	*new_subvolid	= new_subvol->k.p.offset;
+	*new_snapshotid	= new_nodes[0];
+err:
+	bch2_trans_iter_exit(trans, &src_iter);
+	bch2_trans_iter_exit(trans, &dst_iter);
+	return ret;
+}
+
+int bch2_fs_subvolumes_init(struct bch_fs *c)
+{
+	INIT_WORK(&c->snapshot_delete_work, bch2_delete_dead_snapshots_work);
+	return 0;
+}