Adding upstream version 6.7.7.upstream/6.7.7

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2490 insertions, 0 deletions

diff --git a/fs/bcachefs/fsck.c b/fs/bcachefs/fsck.c
new file mode 100644
index 0000000000..e0c5cd119a
--- /dev/null
+++ b/fs/bcachefs/fsck.c
@@ -0,0 +1,2490 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "bcachefs.h"
+#include "bkey_buf.h"
+#include "btree_cache.h"
+#include "btree_update.h"
+#include "buckets.h"
+#include "darray.h"
+#include "dirent.h"
+#include "error.h"
+#include "fs-common.h"
+#include "fsck.h"
+#include "inode.h"
+#include "keylist.h"
+#include "recovery.h"
+#include "snapshot.h"
+#include "super.h"
+#include "xattr.h"
+
+#include <linux/bsearch.h>
+#include <linux/dcache.h> /* struct qstr */
+
+#define QSTR(n) { { { .len = strlen(n) } }, .name = n }
+
+/*
+ * XXX: this is handling transaction restarts without returning
+ * -BCH_ERR_transaction_restart_nested, this is not how we do things anymore:
+ */
+static s64 bch2_count_inode_sectors(struct btree_trans *trans, u64 inum,
+				    u32 snapshot)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	u64 sectors = 0;
+	int ret;
+
+	for_each_btree_key_upto(trans, iter, BTREE_ID_extents,
+				SPOS(inum, 0, snapshot),
+				POS(inum, U64_MAX),
+				0, k, ret)
+		if (bkey_extent_is_allocation(k.k))
+			sectors += k.k->size;
+
+	bch2_trans_iter_exit(trans, &iter);
+
+	return ret ?: sectors;
+}
+
+static s64 bch2_count_subdirs(struct btree_trans *trans, u64 inum,
+				    u32 snapshot)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bkey_s_c_dirent d;
+	u64 subdirs = 0;
+	int ret;
+
+	for_each_btree_key_upto(trans, iter, BTREE_ID_dirents,
+				SPOS(inum, 0, snapshot),
+				POS(inum, U64_MAX),
+				0, k, ret) {
+		if (k.k->type != KEY_TYPE_dirent)
+			continue;
+
+		d = bkey_s_c_to_dirent(k);
+		if (d.v->d_type == DT_DIR)
+			subdirs++;
+	}
+	bch2_trans_iter_exit(trans, &iter);
+
+	return ret ?: subdirs;
+}
+
+static int __snapshot_lookup_subvol(struct btree_trans *trans, u32 snapshot,
+				    u32 *subvol)
+{
+	struct bch_snapshot s;
+	int ret = bch2_bkey_get_val_typed(trans, BTREE_ID_snapshots,
+					  POS(0, snapshot), 0,
+					  snapshot, &s);
+	if (!ret)
+		*subvol = le32_to_cpu(s.subvol);
+	else if (bch2_err_matches(ret, ENOENT))
+		bch_err(trans->c, "snapshot %u not found", snapshot);
+	return ret;
+
+}
+
+static int __subvol_lookup(struct btree_trans *trans, u32 subvol,
+			   u32 *snapshot, u64 *inum)
+{
+	struct bch_subvolume s;
+	int ret;
+
+	ret = bch2_subvolume_get(trans, subvol, false, 0, &s);
+
+	*snapshot = le32_to_cpu(s.snapshot);
+	*inum = le64_to_cpu(s.inode);
+	return ret;
+}
+
+static int subvol_lookup(struct btree_trans *trans, u32 subvol,
+			 u32 *snapshot, u64 *inum)
+{
+	return lockrestart_do(trans, __subvol_lookup(trans, subvol, snapshot, inum));
+}
+
+static int lookup_first_inode(struct btree_trans *trans, u64 inode_nr,
+			      struct bch_inode_unpacked *inode)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_inodes,
+			     POS(0, inode_nr),
+			     BTREE_ITER_ALL_SNAPSHOTS);
+	k = bch2_btree_iter_peek(&iter);
+	ret = bkey_err(k);
+	if (ret)
+		goto err;
+
+	if (!k.k || !bkey_eq(k.k->p, POS(0, inode_nr))) {
+		ret = -BCH_ERR_ENOENT_inode;
+		goto err;
+	}
+
+	ret = bch2_inode_unpack(k, inode);
+err:
+	bch_err_msg(trans->c, ret, "fetching inode %llu", inode_nr);
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static int __lookup_inode(struct btree_trans *trans, u64 inode_nr,
+			  struct bch_inode_unpacked *inode,
+			  u32 *snapshot)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	k = bch2_bkey_get_iter(trans, &iter, BTREE_ID_inodes,
+			       SPOS(0, inode_nr, *snapshot), 0);
+	ret = bkey_err(k);
+	if (ret)
+		goto err;
+
+	ret = bkey_is_inode(k.k)
+		? bch2_inode_unpack(k, inode)
+		: -BCH_ERR_ENOENT_inode;
+	if (!ret)
+		*snapshot = iter.pos.snapshot;
+err:
+	bch_err_msg(trans->c, ret, "fetching inode %llu:%u", inode_nr, *snapshot);
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static int lookup_inode(struct btree_trans *trans, u64 inode_nr,
+			struct bch_inode_unpacked *inode,
+			u32 *snapshot)
+{
+	return lockrestart_do(trans, __lookup_inode(trans, inode_nr, inode, snapshot));
+}
+
+static int __lookup_dirent(struct btree_trans *trans,
+			   struct bch_hash_info hash_info,
+			   subvol_inum dir, struct qstr *name,
+			   u64 *target, unsigned *type)
+{
+	struct btree_iter iter;
+	struct bkey_s_c_dirent d;
+	int ret;
+
+	ret = bch2_hash_lookup(trans, &iter, bch2_dirent_hash_desc,
+			       &hash_info, dir, name, 0);
+	if (ret)
+		return ret;
+
+	d = bkey_s_c_to_dirent(bch2_btree_iter_peek_slot(&iter));
+	*target = le64_to_cpu(d.v->d_inum);
+	*type = d.v->d_type;
+	bch2_trans_iter_exit(trans, &iter);
+	return 0;
+}
+
+static int __write_inode(struct btree_trans *trans,
+			 struct bch_inode_unpacked *inode,
+			 u32 snapshot)
+{
+	struct bkey_inode_buf *inode_p =
+		bch2_trans_kmalloc(trans, sizeof(*inode_p));
+
+	if (IS_ERR(inode_p))
+		return PTR_ERR(inode_p);
+
+	bch2_inode_pack(inode_p, inode);
+	inode_p->inode.k.p.snapshot = snapshot;
+
+	return bch2_btree_insert_nonextent(trans, BTREE_ID_inodes,
+				&inode_p->inode.k_i,
+				BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+}
+
+static int fsck_write_inode(struct btree_trans *trans,
+			    struct bch_inode_unpacked *inode,
+			    u32 snapshot)
+{
+	int ret = commit_do(trans, NULL, NULL,
+				  BTREE_INSERT_NOFAIL|
+				  BTREE_INSERT_LAZY_RW,
+				  __write_inode(trans, inode, snapshot));
+	if (ret)
+		bch_err_fn(trans->c, ret);
+	return ret;
+}
+
+static int __remove_dirent(struct btree_trans *trans, struct bpos pos)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bch_inode_unpacked dir_inode;
+	struct bch_hash_info dir_hash_info;
+	int ret;
+
+	ret = lookup_first_inode(trans, pos.inode, &dir_inode);
+	if (ret)
+		goto err;
+
+	dir_hash_info = bch2_hash_info_init(c, &dir_inode);
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_dirents, pos, BTREE_ITER_INTENT);
+
+	ret = bch2_hash_delete_at(trans, bch2_dirent_hash_desc,
+				  &dir_hash_info, &iter,
+				  BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+	bch2_trans_iter_exit(trans, &iter);
+err:
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+/* Get lost+found, create if it doesn't exist: */
+static int lookup_lostfound(struct btree_trans *trans, u32 subvol,
+			    struct bch_inode_unpacked *lostfound)
+{
+	struct bch_fs *c = trans->c;
+	struct bch_inode_unpacked root;
+	struct bch_hash_info root_hash_info;
+	struct qstr lostfound_str = QSTR("lost+found");
+	subvol_inum root_inum = { .subvol = subvol };
+	u64 inum = 0;
+	unsigned d_type = 0;
+	u32 snapshot;
+	int ret;
+
+	ret = __subvol_lookup(trans, subvol, &snapshot, &root_inum.inum);
+	if (ret)
+		return ret;
+
+	ret = __lookup_inode(trans, root_inum.inum, &root, &snapshot);
+	if (ret)
+		return ret;
+
+	root_hash_info = bch2_hash_info_init(c, &root);
+
+	ret = __lookup_dirent(trans, root_hash_info, root_inum,
+			    &lostfound_str, &inum, &d_type);
+	if (bch2_err_matches(ret, ENOENT)) {
+		bch_notice(c, "creating lost+found");
+		goto create_lostfound;
+	}
+
+	bch_err_fn(c, ret);
+	if (ret)
+		return ret;
+
+	if (d_type != DT_DIR) {
+		bch_err(c, "error looking up lost+found: not a directory");
+		return -BCH_ERR_ENOENT_not_directory;
+	}
+
+	/*
+	 * The bch2_check_dirents pass has already run, dangling dirents
+	 * shouldn't exist here:
+	 */
+	return __lookup_inode(trans, inum, lostfound, &snapshot);
+
+create_lostfound:
+	bch2_inode_init_early(c, lostfound);
+
+	ret = bch2_create_trans(trans, root_inum, &root,
+				lostfound, &lostfound_str,
+				0, 0, S_IFDIR|0700, 0, NULL, NULL,
+				(subvol_inum) { }, 0);
+	bch_err_msg(c, ret, "creating lost+found");
+	return ret;
+}
+
+static int __reattach_inode(struct btree_trans *trans,
+			  struct bch_inode_unpacked *inode,
+			  u32 inode_snapshot)
+{
+	struct bch_hash_info dir_hash;
+	struct bch_inode_unpacked lostfound;
+	char name_buf[20];
+	struct qstr name;
+	u64 dir_offset = 0;
+	u32 subvol;
+	int ret;
+
+	ret = __snapshot_lookup_subvol(trans, inode_snapshot, &subvol);
+	if (ret)
+		return ret;
+
+	ret = lookup_lostfound(trans, subvol, &lostfound);
+	if (ret)
+		return ret;
+
+	if (S_ISDIR(inode->bi_mode)) {
+		lostfound.bi_nlink++;
+
+		ret = __write_inode(trans, &lostfound, U32_MAX);
+		if (ret)
+			return ret;
+	}
+
+	dir_hash = bch2_hash_info_init(trans->c, &lostfound);
+
+	snprintf(name_buf, sizeof(name_buf), "%llu", inode->bi_inum);
+	name = (struct qstr) QSTR(name_buf);
+
+	ret = bch2_dirent_create(trans,
+				 (subvol_inum) {
+					.subvol = subvol,
+					.inum = lostfound.bi_inum,
+				 },
+				 &dir_hash,
+				 inode_d_type(inode),
+				 &name, inode->bi_inum, &dir_offset,
+				 BCH_HASH_SET_MUST_CREATE);
+	if (ret)
+		return ret;
+
+	inode->bi_dir		= lostfound.bi_inum;
+	inode->bi_dir_offset	= dir_offset;
+
+	return __write_inode(trans, inode, inode_snapshot);
+}
+
+static int reattach_inode(struct btree_trans *trans,
+			  struct bch_inode_unpacked *inode,
+			  u32 inode_snapshot)
+{
+	int ret = commit_do(trans, NULL, NULL,
+				  BTREE_INSERT_LAZY_RW|
+				  BTREE_INSERT_NOFAIL,
+			__reattach_inode(trans, inode, inode_snapshot));
+	bch_err_msg(trans->c, ret, "reattaching inode %llu", inode->bi_inum);
+	return ret;
+}
+
+static int remove_backpointer(struct btree_trans *trans,
+			      struct bch_inode_unpacked *inode)
+{
+	struct btree_iter iter;
+	struct bkey_s_c_dirent d;
+	int ret;
+
+	d = bch2_bkey_get_iter_typed(trans, &iter, BTREE_ID_dirents,
+				     POS(inode->bi_dir, inode->bi_dir_offset), 0,
+				     dirent);
+	ret =   bkey_err(d) ?:
+		__remove_dirent(trans, d.k->p);
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+struct snapshots_seen_entry {
+	u32				id;
+	u32				equiv;
+};
+
+struct snapshots_seen {
+	struct bpos			pos;
+	DARRAY(struct snapshots_seen_entry) ids;
+};
+
+static inline void snapshots_seen_exit(struct snapshots_seen *s)
+{
+	darray_exit(&s->ids);
+}
+
+static inline void snapshots_seen_init(struct snapshots_seen *s)
+{
+	memset(s, 0, sizeof(*s));
+}
+
+static int snapshots_seen_add_inorder(struct bch_fs *c, struct snapshots_seen *s, u32 id)
+{
+	struct snapshots_seen_entry *i, n = {
+		.id	= id,
+		.equiv	= bch2_snapshot_equiv(c, id),
+	};
+	int ret = 0;
+
+	darray_for_each(s->ids, i) {
+		if (i->id == id)
+			return 0;
+		if (i->id > id)
+			break;
+	}
+
+	ret = darray_insert_item(&s->ids, i - s->ids.data, n);
+	if (ret)
+		bch_err(c, "error reallocating snapshots_seen table (size %zu)",
+			s->ids.size);
+	return ret;
+}
+
+static int snapshots_seen_update(struct bch_fs *c, struct snapshots_seen *s,
+				 enum btree_id btree_id, struct bpos pos)
+{
+	struct snapshots_seen_entry *i, n = {
+		.id	= pos.snapshot,
+		.equiv	= bch2_snapshot_equiv(c, pos.snapshot),
+	};
+	int ret = 0;
+
+	if (!bkey_eq(s->pos, pos))
+		s->ids.nr = 0;
+
+	s->pos = pos;
+	s->pos.snapshot = n.equiv;
+
+	darray_for_each(s->ids, i) {
+		if (i->id == n.id)
+			return 0;
+
+		/*
+		 * We currently don't rigorously track for snapshot cleanup
+		 * needing to be run, so it shouldn't be a fsck error yet:
+		 */
+		if (i->equiv == n.equiv) {
+			bch_err(c, "snapshot deletion did not finish:\n"
+				"  duplicate keys in btree %s at %llu:%llu snapshots %u, %u (equiv %u)\n",
+				bch2_btree_id_str(btree_id),
+				pos.inode, pos.offset,
+				i->id, n.id, n.equiv);
+			set_bit(BCH_FS_NEED_DELETE_DEAD_SNAPSHOTS, &c->flags);
+			return bch2_run_explicit_recovery_pass(c, BCH_RECOVERY_PASS_delete_dead_snapshots);
+		}
+	}
+
+	ret = darray_push(&s->ids, n);
+	if (ret)
+		bch_err(c, "error reallocating snapshots_seen table (size %zu)",
+			s->ids.size);
+	return ret;
+}
+
+/**
+ * key_visible_in_snapshot - returns true if @id is a descendent of @ancestor,
+ * and @ancestor hasn't been overwritten in @seen
+ *
+ * @c:		filesystem handle
+ * @seen:	list of snapshot ids already seen at current position
+ * @id:		descendent snapshot id
+ * @ancestor:	ancestor snapshot id
+ *
+ * Returns:	whether key in @ancestor snapshot is visible in @id snapshot
+ */
+static bool key_visible_in_snapshot(struct bch_fs *c, struct snapshots_seen *seen,
+				    u32 id, u32 ancestor)
+{
+	ssize_t i;
+
+	EBUG_ON(id > ancestor);
+	EBUG_ON(!bch2_snapshot_is_equiv(c, id));
+	EBUG_ON(!bch2_snapshot_is_equiv(c, ancestor));
+
+	/* @ancestor should be the snapshot most recently added to @seen */
+	EBUG_ON(ancestor != seen->pos.snapshot);
+	EBUG_ON(ancestor != seen->ids.data[seen->ids.nr - 1].equiv);
+
+	if (id == ancestor)
+		return true;
+
+	if (!bch2_snapshot_is_ancestor(c, id, ancestor))
+		return false;
+
+	/*
+	 * We know that @id is a descendant of @ancestor, we're checking if
+	 * we've seen a key that overwrote @ancestor - i.e. also a descendent of
+	 * @ascestor and with @id as a descendent.
+	 *
+	 * But we already know that we're scanning IDs between @id and @ancestor
+	 * numerically, since snapshot ID lists are kept sorted, so if we find
+	 * an id that's an ancestor of @id we're done:
+	 */
+
+	for (i = seen->ids.nr - 2;
+	     i >= 0 && seen->ids.data[i].equiv >= id;
+	     --i)
+		if (bch2_snapshot_is_ancestor(c, id, seen->ids.data[i].equiv))
+			return false;
+
+	return true;
+}
+
+/**
+ * ref_visible - given a key with snapshot id @src that points to a key with
+ * snapshot id @dst, test whether there is some snapshot in which @dst is
+ * visible.
+ *
+ * @c:		filesystem handle
+ * @s:		list of snapshot IDs already seen at @src
+ * @src:	snapshot ID of src key
+ * @dst:	snapshot ID of dst key
+ * Returns:	true if there is some snapshot in which @dst is visible
+ *
+ * Assumes we're visiting @src keys in natural key order
+ */
+static bool ref_visible(struct bch_fs *c, struct snapshots_seen *s,
+			u32 src, u32 dst)
+{
+	return dst <= src
+		? key_visible_in_snapshot(c, s, dst, src)
+		: bch2_snapshot_is_ancestor(c, src, dst);
+}
+
+static int ref_visible2(struct bch_fs *c,
+			u32 src, struct snapshots_seen *src_seen,
+			u32 dst, struct snapshots_seen *dst_seen)
+{
+	src = bch2_snapshot_equiv(c, src);
+	dst = bch2_snapshot_equiv(c, dst);
+
+	if (dst > src) {
+		swap(dst, src);
+		swap(dst_seen, src_seen);
+	}
+	return key_visible_in_snapshot(c, src_seen, dst, src);
+}
+
+#define for_each_visible_inode(_c, _s, _w, _snapshot, _i)				\
+	for (_i = (_w)->inodes.data; _i < (_w)->inodes.data + (_w)->inodes.nr &&	\
+	     (_i)->snapshot <= (_snapshot); _i++)					\
+		if (key_visible_in_snapshot(_c, _s, _i->snapshot, _snapshot))
+
+struct inode_walker_entry {
+	struct bch_inode_unpacked inode;
+	u32			snapshot;
+	bool			seen_this_pos;
+	u64			count;
+};
+
+struct inode_walker {
+	bool				first_this_inode;
+	bool				recalculate_sums;
+	struct bpos			last_pos;
+
+	DARRAY(struct inode_walker_entry) inodes;
+};
+
+static void inode_walker_exit(struct inode_walker *w)
+{
+	darray_exit(&w->inodes);
+}
+
+static struct inode_walker inode_walker_init(void)
+{
+	return (struct inode_walker) { 0, };
+}
+
+static int add_inode(struct bch_fs *c, struct inode_walker *w,
+		     struct bkey_s_c inode)
+{
+	struct bch_inode_unpacked u;
+
+	BUG_ON(bch2_inode_unpack(inode, &u));
+
+	return darray_push(&w->inodes, ((struct inode_walker_entry) {
+		.inode		= u,
+		.snapshot	= bch2_snapshot_equiv(c, inode.k->p.snapshot),
+	}));
+}
+
+static int get_inodes_all_snapshots(struct btree_trans *trans,
+				    struct inode_walker *w, u64 inum)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	u32 restart_count = trans->restart_count;
+	int ret;
+
+	w->recalculate_sums = false;
+	w->inodes.nr = 0;
+
+	for_each_btree_key(trans, iter, BTREE_ID_inodes, POS(0, inum),
+			   BTREE_ITER_ALL_SNAPSHOTS, k, ret) {
+		if (k.k->p.offset != inum)
+			break;
+
+		if (bkey_is_inode(k.k))
+			add_inode(c, w, k);
+	}
+	bch2_trans_iter_exit(trans, &iter);
+
+	if (ret)
+		return ret;
+
+	w->first_this_inode = true;
+
+	return trans_was_restarted(trans, restart_count);
+}
+
+static struct inode_walker_entry *
+lookup_inode_for_snapshot(struct bch_fs *c, struct inode_walker *w,
+			  u32 snapshot, bool is_whiteout)
+{
+	struct inode_walker_entry *i;
+
+	snapshot = bch2_snapshot_equiv(c, snapshot);
+
+	darray_for_each(w->inodes, i)
+		if (bch2_snapshot_is_ancestor(c, snapshot, i->snapshot))
+			goto found;
+
+	return NULL;
+found:
+	BUG_ON(snapshot > i->snapshot);
+
+	if (snapshot != i->snapshot && !is_whiteout) {
+		struct inode_walker_entry new = *i;
+		size_t pos;
+		int ret;
+
+		new.snapshot = snapshot;
+		new.count = 0;
+
+		bch_info(c, "have key for inode %llu:%u but have inode in ancestor snapshot %u",
+			 w->last_pos.inode, snapshot, i->snapshot);
+
+		while (i > w->inodes.data && i[-1].snapshot > snapshot)
+			--i;
+
+		pos = i - w->inodes.data;
+		ret = darray_insert_item(&w->inodes, pos, new);
+		if (ret)
+			return ERR_PTR(ret);
+
+		i = w->inodes.data + pos;
+	}
+
+	return i;
+}
+
+static struct inode_walker_entry *walk_inode(struct btree_trans *trans,
+					     struct inode_walker *w, struct bpos pos,
+					     bool is_whiteout)
+{
+	if (w->last_pos.inode != pos.inode) {
+		int ret = get_inodes_all_snapshots(trans, w, pos.inode);
+		if (ret)
+			return ERR_PTR(ret);
+	} else if (bkey_cmp(w->last_pos, pos)) {
+		struct inode_walker_entry *i;
+
+		darray_for_each(w->inodes, i)
+			i->seen_this_pos = false;
+
+	}
+
+	w->last_pos = pos;
+
+	return lookup_inode_for_snapshot(trans->c, w, pos.snapshot, is_whiteout);
+}
+
+static int __get_visible_inodes(struct btree_trans *trans,
+				struct inode_walker *w,
+				struct snapshots_seen *s,
+				u64 inum)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	w->inodes.nr = 0;
+
+	for_each_btree_key_norestart(trans, iter, BTREE_ID_inodes, POS(0, inum),
+			   BTREE_ITER_ALL_SNAPSHOTS, k, ret) {
+		u32 equiv = bch2_snapshot_equiv(c, k.k->p.snapshot);
+
+		if (k.k->p.offset != inum)
+			break;
+
+		if (!ref_visible(c, s, s->pos.snapshot, equiv))
+			continue;
+
+		if (bkey_is_inode(k.k))
+			add_inode(c, w, k);
+
+		if (equiv >= s->pos.snapshot)
+			break;
+	}
+	bch2_trans_iter_exit(trans, &iter);
+
+	return ret;
+}
+
+static int check_key_has_snapshot(struct btree_trans *trans,
+				  struct btree_iter *iter,
+				  struct bkey_s_c k)
+{
+	struct bch_fs *c = trans->c;
+	struct printbuf buf = PRINTBUF;
+	int ret = 0;
+
+	if (mustfix_fsck_err_on(!bch2_snapshot_equiv(c, k.k->p.snapshot), c,
+				bkey_in_missing_snapshot,
+				"key in missing snapshot: %s",
+				(bch2_bkey_val_to_text(&buf, c, k), buf.buf)))
+		ret = bch2_btree_delete_at(trans, iter,
+					    BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE) ?: 1;
+fsck_err:
+	printbuf_exit(&buf);
+	return ret;
+}
+
+static int hash_redo_key(struct btree_trans *trans,
+			 const struct bch_hash_desc desc,
+			 struct bch_hash_info *hash_info,
+			 struct btree_iter *k_iter, struct bkey_s_c k)
+{
+	struct bkey_i *delete;
+	struct bkey_i *tmp;
+
+	delete = bch2_trans_kmalloc(trans, sizeof(*delete));
+	if (IS_ERR(delete))
+		return PTR_ERR(delete);
+
+	tmp = bch2_bkey_make_mut_noupdate(trans, k);
+	if (IS_ERR(tmp))
+		return PTR_ERR(tmp);
+
+	bkey_init(&delete->k);
+	delete->k.p = k_iter->pos;
+	return  bch2_btree_iter_traverse(k_iter) ?:
+		bch2_trans_update(trans, k_iter, delete, 0) ?:
+		bch2_hash_set_snapshot(trans, desc, hash_info,
+				       (subvol_inum) { 0, k.k->p.inode },
+				       k.k->p.snapshot, tmp,
+				       BCH_HASH_SET_MUST_CREATE,
+				       BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE) ?:
+		bch2_trans_commit(trans, NULL, NULL,
+				  BTREE_INSERT_NOFAIL|
+				  BTREE_INSERT_LAZY_RW);
+}
+
+static int hash_check_key(struct btree_trans *trans,
+			  const struct bch_hash_desc desc,
+			  struct bch_hash_info *hash_info,
+			  struct btree_iter *k_iter, struct bkey_s_c hash_k)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter = { NULL };
+	struct printbuf buf = PRINTBUF;
+	struct bkey_s_c k;
+	u64 hash;
+	int ret = 0;
+
+	if (hash_k.k->type != desc.key_type)
+		return 0;
+
+	hash = desc.hash_bkey(hash_info, hash_k);
+
+	if (likely(hash == hash_k.k->p.offset))
+		return 0;
+
+	if (hash_k.k->p.offset < hash)
+		goto bad_hash;
+
+	for_each_btree_key_norestart(trans, iter, desc.btree_id,
+				     SPOS(hash_k.k->p.inode, hash, hash_k.k->p.snapshot),
+				     BTREE_ITER_SLOTS, k, ret) {
+		if (bkey_eq(k.k->p, hash_k.k->p))
+			break;
+
+		if (fsck_err_on(k.k->type == desc.key_type &&
+				!desc.cmp_bkey(k, hash_k), c,
+				hash_table_key_duplicate,
+				"duplicate hash table keys:\n%s",
+				(printbuf_reset(&buf),
+				 bch2_bkey_val_to_text(&buf, c, hash_k),
+				 buf.buf))) {
+			ret = bch2_hash_delete_at(trans, desc, hash_info, k_iter, 0) ?: 1;
+			break;
+		}
+
+		if (bkey_deleted(k.k)) {
+			bch2_trans_iter_exit(trans, &iter);
+			goto bad_hash;
+		}
+	}
+out:
+	bch2_trans_iter_exit(trans, &iter);
+	printbuf_exit(&buf);
+	return ret;
+bad_hash:
+	if (fsck_err(c, hash_table_key_wrong_offset,
+		     "hash table key at wrong offset: btree %s inode %llu offset %llu, hashed to %llu\n%s",
+		     bch2_btree_id_str(desc.btree_id), hash_k.k->p.inode, hash_k.k->p.offset, hash,
+		     (printbuf_reset(&buf),
+		      bch2_bkey_val_to_text(&buf, c, hash_k), buf.buf))) {
+		ret = hash_redo_key(trans, desc, hash_info, k_iter, hash_k);
+		bch_err_fn(c, ret);
+		if (ret)
+			return ret;
+		ret = -BCH_ERR_transaction_restart_nested;
+	}
+fsck_err:
+	goto out;
+}
+
+static int check_inode(struct btree_trans *trans,
+		       struct btree_iter *iter,
+		       struct bkey_s_c k,
+		       struct bch_inode_unpacked *prev,
+		       struct snapshots_seen *s,
+		       bool full)
+{
+	struct bch_fs *c = trans->c;
+	struct bch_inode_unpacked u;
+	bool do_update = false;
+	int ret;
+
+	ret = check_key_has_snapshot(trans, iter, k);
+	if (ret < 0)
+		goto err;
+	if (ret)
+		return 0;
+
+	ret = snapshots_seen_update(c, s, iter->btree_id, k.k->p);
+	if (ret)
+		goto err;
+
+	if (!bkey_is_inode(k.k))
+		return 0;
+
+	BUG_ON(bch2_inode_unpack(k, &u));
+
+	if (!full &&
+	    !(u.bi_flags & (BCH_INODE_i_size_dirty|
+			    BCH_INODE_i_sectors_dirty|
+			    BCH_INODE_unlinked)))
+		return 0;
+
+	if (prev->bi_inum != u.bi_inum)
+		*prev = u;
+
+	if (fsck_err_on(prev->bi_hash_seed	!= u.bi_hash_seed ||
+			inode_d_type(prev)	!= inode_d_type(&u),
+			c, inode_snapshot_mismatch,
+			"inodes in different snapshots don't match")) {
+		bch_err(c, "repair not implemented yet");
+		return -EINVAL;
+	}
+
+	if ((u.bi_flags & (BCH_INODE_i_size_dirty|BCH_INODE_unlinked)) &&
+	    bch2_key_has_snapshot_overwrites(trans, BTREE_ID_inodes, k.k->p)) {
+		struct bpos new_min_pos;
+
+		ret = bch2_propagate_key_to_snapshot_leaves(trans, iter->btree_id, k, &new_min_pos);
+		if (ret)
+			goto err;
+
+		u.bi_flags &= ~BCH_INODE_i_size_dirty|BCH_INODE_unlinked;
+
+		ret = __write_inode(trans, &u, iter->pos.snapshot);
+		bch_err_msg(c, ret, "in fsck updating inode");
+		if (ret)
+			return ret;
+
+		if (!bpos_eq(new_min_pos, POS_MIN))
+			bch2_btree_iter_set_pos(iter, bpos_predecessor(new_min_pos));
+		return 0;
+	}
+
+	if (u.bi_flags & BCH_INODE_unlinked &&
+	    (!c->sb.clean ||
+	     fsck_err(c, inode_unlinked_but_clean,
+		      "filesystem marked clean, but inode %llu unlinked",
+		      u.bi_inum))) {
+		bch2_trans_unlock(trans);
+		bch2_fs_lazy_rw(c);
+
+		ret = bch2_inode_rm_snapshot(trans, u.bi_inum, iter->pos.snapshot);
+		bch_err_msg(c, ret, "in fsck deleting inode");
+		return ret;
+	}
+
+	if (u.bi_flags & BCH_INODE_i_size_dirty &&
+	    (!c->sb.clean ||
+	     fsck_err(c, inode_i_size_dirty_but_clean,
+		      "filesystem marked clean, but inode %llu has i_size dirty",
+		      u.bi_inum))) {
+		bch_verbose(c, "truncating inode %llu", u.bi_inum);
+
+		bch2_trans_unlock(trans);
+		bch2_fs_lazy_rw(c);
+
+		/*
+		 * XXX: need to truncate partial blocks too here - or ideally
+		 * just switch units to bytes and that issue goes away
+		 */
+		ret = bch2_btree_delete_range_trans(trans, BTREE_ID_extents,
+				SPOS(u.bi_inum, round_up(u.bi_size, block_bytes(c)) >> 9,
+				     iter->pos.snapshot),
+				POS(u.bi_inum, U64_MAX),
+				0, NULL);
+		bch_err_msg(c, ret, "in fsck truncating inode");
+		if (ret)
+			return ret;
+
+		/*
+		 * We truncated without our normal sector accounting hook, just
+		 * make sure we recalculate it:
+		 */
+		u.bi_flags |= BCH_INODE_i_sectors_dirty;
+
+		u.bi_flags &= ~BCH_INODE_i_size_dirty;
+		do_update = true;
+	}
+
+	if (u.bi_flags & BCH_INODE_i_sectors_dirty &&
+	    (!c->sb.clean ||
+	     fsck_err(c, inode_i_sectors_dirty_but_clean,
+		      "filesystem marked clean, but inode %llu has i_sectors dirty",
+		      u.bi_inum))) {
+		s64 sectors;
+
+		bch_verbose(c, "recounting sectors for inode %llu",
+			    u.bi_inum);
+
+		sectors = bch2_count_inode_sectors(trans, u.bi_inum, iter->pos.snapshot);
+		if (sectors < 0) {
+			bch_err_msg(c, sectors, "in fsck recounting inode sectors");
+			return sectors;
+		}
+
+		u.bi_sectors = sectors;
+		u.bi_flags &= ~BCH_INODE_i_sectors_dirty;
+		do_update = true;
+	}
+
+	if (u.bi_flags & BCH_INODE_backptr_untrusted) {
+		u.bi_dir = 0;
+		u.bi_dir_offset = 0;
+		u.bi_flags &= ~BCH_INODE_backptr_untrusted;
+		do_update = true;
+	}
+
+	if (do_update) {
+		ret = __write_inode(trans, &u, iter->pos.snapshot);
+		bch_err_msg(c, ret, "in fsck updating inode");
+		if (ret)
+			return ret;
+	}
+err:
+fsck_err:
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+noinline_for_stack
+int bch2_check_inodes(struct bch_fs *c)
+{
+	bool full = c->opts.fsck;
+	struct btree_trans *trans = bch2_trans_get(c);
+	struct btree_iter iter;
+	struct bch_inode_unpacked prev = { 0 };
+	struct snapshots_seen s;
+	struct bkey_s_c k;
+	int ret;
+
+	snapshots_seen_init(&s);
+
+	ret = for_each_btree_key_commit(trans, iter, BTREE_ID_inodes,
+			POS_MIN,
+			BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS, k,
+			NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
+		check_inode(trans, &iter, k, &prev, &s, full));
+
+	snapshots_seen_exit(&s);
+	bch2_trans_put(trans);
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+static struct bkey_s_c_dirent dirent_get_by_pos(struct btree_trans *trans,
+						struct btree_iter *iter,
+						struct bpos pos)
+{
+	return bch2_bkey_get_iter_typed(trans, iter, BTREE_ID_dirents, pos, 0, dirent);
+}
+
+static bool inode_points_to_dirent(struct bch_inode_unpacked *inode,
+				   struct bkey_s_c_dirent d)
+{
+	return  inode->bi_dir		== d.k->p.inode &&
+		inode->bi_dir_offset	== d.k->p.offset;
+}
+
+static bool dirent_points_to_inode(struct bkey_s_c_dirent d,
+				   struct bch_inode_unpacked *inode)
+{
+	return d.v->d_type == DT_SUBVOL
+		? le32_to_cpu(d.v->d_child_subvol)	== inode->bi_subvol
+		: le64_to_cpu(d.v->d_inum)		== inode->bi_inum;
+}
+
+static int inode_backpointer_exists(struct btree_trans *trans,
+				    struct bch_inode_unpacked *inode,
+				    u32 snapshot)
+{
+	struct btree_iter iter;
+	struct bkey_s_c_dirent d;
+	int ret;
+
+	d = dirent_get_by_pos(trans, &iter,
+			SPOS(inode->bi_dir, inode->bi_dir_offset, snapshot));
+	ret = bkey_err(d);
+	if (ret)
+		return bch2_err_matches(ret, ENOENT) ? 0 : ret;
+
+	ret = dirent_points_to_inode(d, inode);
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static int check_i_sectors(struct btree_trans *trans, struct inode_walker *w)
+{
+	struct bch_fs *c = trans->c;
+	struct inode_walker_entry *i;
+	u32 restart_count = trans->restart_count;
+	int ret = 0;
+	s64 count2;
+
+	darray_for_each(w->inodes, i) {
+		if (i->inode.bi_sectors == i->count)
+			continue;
+
+		count2 = bch2_count_inode_sectors(trans, w->last_pos.inode, i->snapshot);
+
+		if (w->recalculate_sums)
+			i->count = count2;
+
+		if (i->count != count2) {
+			bch_err(c, "fsck counted i_sectors wrong for inode %llu:%u: got %llu should be %llu",
+				w->last_pos.inode, i->snapshot, i->count, count2);
+			return -BCH_ERR_internal_fsck_err;
+		}
+
+		if (fsck_err_on(!(i->inode.bi_flags & BCH_INODE_i_sectors_dirty),
+				c, inode_i_sectors_wrong,
+				"inode %llu:%u has incorrect i_sectors: got %llu, should be %llu",
+				w->last_pos.inode, i->snapshot,
+				i->inode.bi_sectors, i->count)) {
+			i->inode.bi_sectors = i->count;
+			ret = fsck_write_inode(trans, &i->inode, i->snapshot);
+			if (ret)
+				break;
+		}
+	}
+fsck_err:
+	bch_err_fn(c, ret);
+	return ret ?: trans_was_restarted(trans, restart_count);
+}
+
+struct extent_end {
+	u32			snapshot;
+	u64			offset;
+	struct snapshots_seen	seen;
+};
+
+struct extent_ends {
+	struct bpos			last_pos;
+	DARRAY(struct extent_end)	e;
+};
+
+static void extent_ends_reset(struct extent_ends *extent_ends)
+{
+	struct extent_end *i;
+
+	darray_for_each(extent_ends->e, i)
+		snapshots_seen_exit(&i->seen);
+
+	extent_ends->e.nr = 0;
+}
+
+static void extent_ends_exit(struct extent_ends *extent_ends)
+{
+	extent_ends_reset(extent_ends);
+	darray_exit(&extent_ends->e);
+}
+
+static void extent_ends_init(struct extent_ends *extent_ends)
+{
+	memset(extent_ends, 0, sizeof(*extent_ends));
+}
+
+static int extent_ends_at(struct bch_fs *c,
+			  struct extent_ends *extent_ends,
+			  struct snapshots_seen *seen,
+			  struct bkey_s_c k)
+{
+	struct extent_end *i, n = (struct extent_end) {
+		.offset		= k.k->p.offset,
+		.snapshot	= k.k->p.snapshot,
+		.seen		= *seen,
+	};
+
+	n.seen.ids.data = kmemdup(seen->ids.data,
+			      sizeof(seen->ids.data[0]) * seen->ids.size,
+			      GFP_KERNEL);
+	if (!n.seen.ids.data)
+		return -BCH_ERR_ENOMEM_fsck_extent_ends_at;
+
+	darray_for_each(extent_ends->e, i) {
+		if (i->snapshot == k.k->p.snapshot) {
+			snapshots_seen_exit(&i->seen);
+			*i = n;
+			return 0;
+		}
+
+		if (i->snapshot >= k.k->p.snapshot)
+			break;
+	}
+
+	return darray_insert_item(&extent_ends->e, i - extent_ends->e.data, n);
+}
+
+static int overlapping_extents_found(struct btree_trans *trans,
+				     enum btree_id btree,
+				     struct bpos pos1, struct snapshots_seen *pos1_seen,
+				     struct bkey pos2,
+				     bool *fixed,
+				     struct extent_end *extent_end)
+{
+	struct bch_fs *c = trans->c;
+	struct printbuf buf = PRINTBUF;
+	struct btree_iter iter1, iter2 = { NULL };
+	struct bkey_s_c k1, k2;
+	int ret;
+
+	BUG_ON(bkey_le(pos1, bkey_start_pos(&pos2)));
+
+	bch2_trans_iter_init(trans, &iter1, btree, pos1,
+			     BTREE_ITER_ALL_SNAPSHOTS|
+			     BTREE_ITER_NOT_EXTENTS);
+	k1 = bch2_btree_iter_peek_upto(&iter1, POS(pos1.inode, U64_MAX));
+	ret = bkey_err(k1);
+	if (ret)
+		goto err;
+
+	prt_str(&buf, "\n  ");
+	bch2_bkey_val_to_text(&buf, c, k1);
+
+	if (!bpos_eq(pos1, k1.k->p)) {
+		prt_str(&buf, "\n  wanted\n  ");
+		bch2_bpos_to_text(&buf, pos1);
+		prt_str(&buf, "\n  ");
+		bch2_bkey_to_text(&buf, &pos2);
+
+		bch_err(c, "%s: error finding first overlapping extent when repairing, got%s",
+			__func__, buf.buf);
+		ret = -BCH_ERR_internal_fsck_err;
+		goto err;
+	}
+
+	bch2_trans_copy_iter(&iter2, &iter1);
+
+	while (1) {
+		bch2_btree_iter_advance(&iter2);
+
+		k2 = bch2_btree_iter_peek_upto(&iter2, POS(pos1.inode, U64_MAX));
+		ret = bkey_err(k2);
+		if (ret)
+			goto err;
+
+		if (bpos_ge(k2.k->p, pos2.p))
+			break;
+	}
+
+	prt_str(&buf, "\n  ");
+	bch2_bkey_val_to_text(&buf, c, k2);
+
+	if (bpos_gt(k2.k->p, pos2.p) ||
+	    pos2.size != k2.k->size) {
+		bch_err(c, "%s: error finding seconding overlapping extent when repairing%s",
+			__func__, buf.buf);
+		ret = -BCH_ERR_internal_fsck_err;
+		goto err;
+	}
+
+	prt_printf(&buf, "\n  overwriting %s extent",
+		   pos1.snapshot >= pos2.p.snapshot ? "first" : "second");
+
+	if (fsck_err(c, extent_overlapping,
+		     "overlapping extents%s", buf.buf)) {
+		struct btree_iter *old_iter = &iter1;
+		struct disk_reservation res = { 0 };
+
+		if (pos1.snapshot < pos2.p.snapshot) {
+			old_iter = &iter2;
+			swap(k1, k2);
+		}
+
+		trans->extra_journal_res += bch2_bkey_sectors_compressed(k2);
+
+		ret =   bch2_trans_update_extent_overwrite(trans, old_iter,
+				BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE,
+				k1, k2) ?:
+			bch2_trans_commit(trans, &res, NULL,
+				BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL);
+		bch2_disk_reservation_put(c, &res);
+
+		if (ret)
+			goto err;
+
+		*fixed = true;
+
+		if (pos1.snapshot == pos2.p.snapshot) {
+			/*
+			 * We overwrote the first extent, and did the overwrite
+			 * in the same snapshot:
+			 */
+			extent_end->offset = bkey_start_offset(&pos2);
+		} else if (pos1.snapshot > pos2.p.snapshot) {
+			/*
+			 * We overwrote the first extent in pos2's snapshot:
+			 */
+			ret = snapshots_seen_add_inorder(c, pos1_seen, pos2.p.snapshot);
+		} else {
+			/*
+			 * We overwrote the second extent - restart
+			 * check_extent() from the top:
+			 */
+			ret = -BCH_ERR_transaction_restart_nested;
+		}
+	}
+fsck_err:
+err:
+	bch2_trans_iter_exit(trans, &iter2);
+	bch2_trans_iter_exit(trans, &iter1);
+	printbuf_exit(&buf);
+	return ret;
+}
+
+static int check_overlapping_extents(struct btree_trans *trans,
+			      struct snapshots_seen *seen,
+			      struct extent_ends *extent_ends,
+			      struct bkey_s_c k,
+			      u32 equiv,
+			      struct btree_iter *iter,
+			      bool *fixed)
+{
+	struct bch_fs *c = trans->c;
+	struct extent_end *i;
+	int ret = 0;
+
+	/* transaction restart, running again */
+	if (bpos_eq(extent_ends->last_pos, k.k->p))
+		return 0;
+
+	if (extent_ends->last_pos.inode != k.k->p.inode)
+		extent_ends_reset(extent_ends);
+
+	darray_for_each(extent_ends->e, i) {
+		if (i->offset <= bkey_start_offset(k.k))
+			continue;
+
+		if (!ref_visible2(c,
+				  k.k->p.snapshot, seen,
+				  i->snapshot, &i->seen))
+			continue;
+
+		ret = overlapping_extents_found(trans, iter->btree_id,
+						SPOS(iter->pos.inode,
+						     i->offset,
+						     i->snapshot),
+						&i->seen,
+						*k.k, fixed, i);
+		if (ret)
+			goto err;
+	}
+
+	ret = extent_ends_at(c, extent_ends, seen, k);
+	if (ret)
+		goto err;
+
+	extent_ends->last_pos = k.k->p;
+err:
+	return ret;
+}
+
+static int check_extent_overbig(struct btree_trans *trans, struct btree_iter *iter,
+				struct bkey_s_c k)
+{
+	struct bch_fs *c = trans->c;
+	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
+	struct bch_extent_crc_unpacked crc;
+	const union bch_extent_entry *i;
+	unsigned encoded_extent_max_sectors = c->opts.encoded_extent_max >> 9;
+
+	bkey_for_each_crc(k.k, ptrs, crc, i)
+		if (crc_is_encoded(crc) &&
+		    crc.uncompressed_size > encoded_extent_max_sectors) {
+			struct printbuf buf = PRINTBUF;
+
+			bch2_bkey_val_to_text(&buf, c, k);
+			bch_err(c, "overbig encoded extent, please report this:\n  %s", buf.buf);
+			printbuf_exit(&buf);
+		}
+
+	return 0;
+}
+
+static int check_extent(struct btree_trans *trans, struct btree_iter *iter,
+			struct bkey_s_c k,
+			struct inode_walker *inode,
+			struct snapshots_seen *s,
+			struct extent_ends *extent_ends)
+{
+	struct bch_fs *c = trans->c;
+	struct inode_walker_entry *i;
+	struct printbuf buf = PRINTBUF;
+	struct bpos equiv = k.k->p;
+	int ret = 0;
+
+	equiv.snapshot = bch2_snapshot_equiv(c, k.k->p.snapshot);
+
+	ret = check_key_has_snapshot(trans, iter, k);
+	if (ret) {
+		ret = ret < 0 ? ret : 0;
+		goto out;
+	}
+
+	if (inode->last_pos.inode != k.k->p.inode) {
+		ret = check_i_sectors(trans, inode);
+		if (ret)
+			goto err;
+	}
+
+	i = walk_inode(trans, inode, equiv, k.k->type == KEY_TYPE_whiteout);
+	ret = PTR_ERR_OR_ZERO(i);
+	if (ret)
+		goto err;
+
+	ret = snapshots_seen_update(c, s, iter->btree_id, k.k->p);
+	if (ret)
+		goto err;
+
+	if (k.k->type != KEY_TYPE_whiteout) {
+		if (fsck_err_on(!i, c, extent_in_missing_inode,
+				"extent in missing inode:\n  %s",
+				(printbuf_reset(&buf),
+				 bch2_bkey_val_to_text(&buf, c, k), buf.buf)))
+			goto delete;
+
+		if (fsck_err_on(i &&
+				!S_ISREG(i->inode.bi_mode) &&
+				!S_ISLNK(i->inode.bi_mode),
+				c, extent_in_non_reg_inode,
+				"extent in non regular inode mode %o:\n  %s",
+				i->inode.bi_mode,
+				(printbuf_reset(&buf),
+				 bch2_bkey_val_to_text(&buf, c, k), buf.buf)))
+			goto delete;
+
+		ret = check_overlapping_extents(trans, s, extent_ends, k,
+						equiv.snapshot, iter,
+						&inode->recalculate_sums);
+		if (ret)
+			goto err;
+	}
+
+	/*
+	 * Check inodes in reverse order, from oldest snapshots to newest,
+	 * starting from the inode that matches this extent's snapshot. If we
+	 * didn't have one, iterate over all inodes:
+	 */
+	if (!i)
+		i = inode->inodes.data + inode->inodes.nr - 1;
+
+	for (;
+	     inode->inodes.data && i >= inode->inodes.data;
+	     --i) {
+		if (i->snapshot > equiv.snapshot ||
+		    !key_visible_in_snapshot(c, s, i->snapshot, equiv.snapshot))
+			continue;
+
+		if (k.k->type != KEY_TYPE_whiteout) {
+			if (fsck_err_on(!(i->inode.bi_flags & BCH_INODE_i_size_dirty) &&
+					k.k->p.offset > round_up(i->inode.bi_size, block_bytes(c)) >> 9 &&
+					!bkey_extent_is_reservation(k),
+					c, extent_past_end_of_inode,
+					"extent type past end of inode %llu:%u, i_size %llu\n  %s",
+					i->inode.bi_inum, i->snapshot, i->inode.bi_size,
+					(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+				struct btree_iter iter2;
+
+				bch2_trans_copy_iter(&iter2, iter);
+				bch2_btree_iter_set_snapshot(&iter2, i->snapshot);
+				ret =   bch2_btree_iter_traverse(&iter2) ?:
+					bch2_btree_delete_at(trans, &iter2,
+						BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+				bch2_trans_iter_exit(trans, &iter2);
+				if (ret)
+					goto err;
+
+				iter->k.type = KEY_TYPE_whiteout;
+			}
+
+			if (bkey_extent_is_allocation(k.k))
+				i->count += k.k->size;
+		}
+
+		i->seen_this_pos = true;
+	}
+out:
+err:
+fsck_err:
+	printbuf_exit(&buf);
+	bch_err_fn(c, ret);
+	return ret;
+delete:
+	ret = bch2_btree_delete_at(trans, iter, BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+	goto out;
+}
+
+/*
+ * Walk extents: verify that extents have a corresponding S_ISREG inode, and
+ * that i_size an i_sectors are consistent
+ */
+int bch2_check_extents(struct bch_fs *c)
+{
+	struct inode_walker w = inode_walker_init();
+	struct snapshots_seen s;
+	struct btree_trans *trans = bch2_trans_get(c);
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct extent_ends extent_ends;
+	struct disk_reservation res = { 0 };
+	int ret = 0;
+
+	snapshots_seen_init(&s);
+	extent_ends_init(&extent_ends);
+
+	ret = for_each_btree_key_commit(trans, iter, BTREE_ID_extents,
+			POS(BCACHEFS_ROOT_INO, 0),
+			BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS, k,
+			&res, NULL,
+			BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL, ({
+		bch2_disk_reservation_put(c, &res);
+		check_extent(trans, &iter, k, &w, &s, &extent_ends) ?:
+		check_extent_overbig(trans, &iter, k);
+	})) ?:
+	check_i_sectors(trans, &w);
+
+	bch2_disk_reservation_put(c, &res);
+	extent_ends_exit(&extent_ends);
+	inode_walker_exit(&w);
+	snapshots_seen_exit(&s);
+	bch2_trans_put(trans);
+
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+int bch2_check_indirect_extents(struct bch_fs *c)
+{
+	struct btree_trans *trans = bch2_trans_get(c);
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct disk_reservation res = { 0 };
+	int ret = 0;
+
+	ret = for_each_btree_key_commit(trans, iter, BTREE_ID_reflink,
+			POS_MIN,
+			BTREE_ITER_PREFETCH, k,
+			&res, NULL,
+			BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL, ({
+		bch2_disk_reservation_put(c, &res);
+		check_extent_overbig(trans, &iter, k);
+	}));
+
+	bch2_disk_reservation_put(c, &res);
+	bch2_trans_put(trans);
+
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+static int check_subdir_count(struct btree_trans *trans, struct inode_walker *w)
+{
+	struct bch_fs *c = trans->c;
+	struct inode_walker_entry *i;
+	u32 restart_count = trans->restart_count;
+	int ret = 0;
+	s64 count2;
+
+	darray_for_each(w->inodes, i) {
+		if (i->inode.bi_nlink == i->count)
+			continue;
+
+		count2 = bch2_count_subdirs(trans, w->last_pos.inode, i->snapshot);
+		if (count2 < 0)
+			return count2;
+
+		if (i->count != count2) {
+			bch_err(c, "fsck counted subdirectories wrong: got %llu should be %llu",
+				i->count, count2);
+			i->count = count2;
+			if (i->inode.bi_nlink == i->count)
+				continue;
+		}
+
+		if (fsck_err_on(i->inode.bi_nlink != i->count,
+				c, inode_dir_wrong_nlink,
+				"directory %llu:%u with wrong i_nlink: got %u, should be %llu",
+				w->last_pos.inode, i->snapshot, i->inode.bi_nlink, i->count)) {
+			i->inode.bi_nlink = i->count;
+			ret = fsck_write_inode(trans, &i->inode, i->snapshot);
+			if (ret)
+				break;
+		}
+	}
+fsck_err:
+	bch_err_fn(c, ret);
+	return ret ?: trans_was_restarted(trans, restart_count);
+}
+
+static int check_dirent_target(struct btree_trans *trans,
+			       struct btree_iter *iter,
+			       struct bkey_s_c_dirent d,
+			       struct bch_inode_unpacked *target,
+			       u32 target_snapshot)
+{
+	struct bch_fs *c = trans->c;
+	struct bkey_i_dirent *n;
+	bool backpointer_exists = true;
+	struct printbuf buf = PRINTBUF;
+	int ret = 0;
+
+	if (!target->bi_dir &&
+	    !target->bi_dir_offset) {
+		target->bi_dir		= d.k->p.inode;
+		target->bi_dir_offset	= d.k->p.offset;
+
+		ret = __write_inode(trans, target, target_snapshot);
+		if (ret)
+			goto err;
+	}
+
+	if (!inode_points_to_dirent(target, d)) {
+		ret = inode_backpointer_exists(trans, target, d.k->p.snapshot);
+		if (ret < 0)
+			goto err;
+
+		backpointer_exists = ret;
+		ret = 0;
+
+		if (fsck_err_on(S_ISDIR(target->bi_mode) && backpointer_exists,
+				c, inode_dir_multiple_links,
+				"directory %llu with multiple links",
+				target->bi_inum)) {
+			ret = __remove_dirent(trans, d.k->p);
+			goto out;
+		}
+
+		if (fsck_err_on(backpointer_exists && !target->bi_nlink,
+				c, inode_multiple_links_but_nlink_0,
+				"inode %llu type %s has multiple links but i_nlink 0",
+				target->bi_inum, bch2_d_types[d.v->d_type])) {
+			target->bi_nlink++;
+			target->bi_flags &= ~BCH_INODE_unlinked;
+
+			ret = __write_inode(trans, target, target_snapshot);
+			if (ret)
+				goto err;
+		}
+
+		if (fsck_err_on(!backpointer_exists,
+				c, inode_wrong_backpointer,
+				"inode %llu:%u has wrong backpointer:\n"
+				"got       %llu:%llu\n"
+				"should be %llu:%llu",
+				target->bi_inum, target_snapshot,
+				target->bi_dir,
+				target->bi_dir_offset,
+				d.k->p.inode,
+				d.k->p.offset)) {
+			target->bi_dir		= d.k->p.inode;
+			target->bi_dir_offset	= d.k->p.offset;
+
+			ret = __write_inode(trans, target, target_snapshot);
+			if (ret)
+				goto err;
+		}
+	}
+
+	if (fsck_err_on(d.v->d_type != inode_d_type(target),
+			c, dirent_d_type_wrong,
+			"incorrect d_type: got %s, should be %s:\n%s",
+			bch2_d_type_str(d.v->d_type),
+			bch2_d_type_str(inode_d_type(target)),
+			(printbuf_reset(&buf),
+			 bch2_bkey_val_to_text(&buf, c, d.s_c), buf.buf))) {
+		n = bch2_trans_kmalloc(trans, bkey_bytes(d.k));
+		ret = PTR_ERR_OR_ZERO(n);
+		if (ret)
+			goto err;
+
+		bkey_reassemble(&n->k_i, d.s_c);
+		n->v.d_type = inode_d_type(target);
+
+		ret = bch2_trans_update(trans, iter, &n->k_i, 0);
+		if (ret)
+			goto err;
+
+		d = dirent_i_to_s_c(n);
+	}
+
+	if (d.v->d_type == DT_SUBVOL &&
+	    target->bi_parent_subvol != le32_to_cpu(d.v->d_parent_subvol) &&
+	    (c->sb.version < bcachefs_metadata_version_subvol_dirent ||
+	     fsck_err(c, dirent_d_parent_subvol_wrong,
+		      "dirent has wrong d_parent_subvol field: got %u, should be %u",
+		      le32_to_cpu(d.v->d_parent_subvol),
+		      target->bi_parent_subvol))) {
+		n = bch2_trans_kmalloc(trans, bkey_bytes(d.k));
+		ret = PTR_ERR_OR_ZERO(n);
+		if (ret)
+			goto err;
+
+		bkey_reassemble(&n->k_i, d.s_c);
+		n->v.d_parent_subvol = cpu_to_le32(target->bi_parent_subvol);
+
+		ret = bch2_trans_update(trans, iter, &n->k_i, 0);
+		if (ret)
+			goto err;
+
+		d = dirent_i_to_s_c(n);
+	}
+out:
+err:
+fsck_err:
+	printbuf_exit(&buf);
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+static int check_dirent(struct btree_trans *trans, struct btree_iter *iter,
+			struct bkey_s_c k,
+			struct bch_hash_info *hash_info,
+			struct inode_walker *dir,
+			struct inode_walker *target,
+			struct snapshots_seen *s)
+{
+	struct bch_fs *c = trans->c;
+	struct bkey_s_c_dirent d;
+	struct inode_walker_entry *i;
+	struct printbuf buf = PRINTBUF;
+	struct bpos equiv;
+	int ret = 0;
+
+	ret = check_key_has_snapshot(trans, iter, k);
+	if (ret) {
+		ret = ret < 0 ? ret : 0;
+		goto out;
+	}
+
+	equiv = k.k->p;
+	equiv.snapshot = bch2_snapshot_equiv(c, k.k->p.snapshot);
+
+	ret = snapshots_seen_update(c, s, iter->btree_id, k.k->p);
+	if (ret)
+		goto err;
+
+	if (k.k->type == KEY_TYPE_whiteout)
+		goto out;
+
+	if (dir->last_pos.inode != k.k->p.inode) {
+		ret = check_subdir_count(trans, dir);
+		if (ret)
+			goto err;
+	}
+
+	BUG_ON(!iter->path->should_be_locked);
+
+	i = walk_inode(trans, dir, equiv, k.k->type == KEY_TYPE_whiteout);
+	ret = PTR_ERR_OR_ZERO(i);
+	if (ret < 0)
+		goto err;
+
+	if (dir->first_this_inode && dir->inodes.nr)
+		*hash_info = bch2_hash_info_init(c, &dir->inodes.data[0].inode);
+	dir->first_this_inode = false;
+
+	if (fsck_err_on(!i, c, dirent_in_missing_dir_inode,
+			"dirent in nonexisting directory:\n%s",
+			(printbuf_reset(&buf),
+			 bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+		ret = bch2_btree_delete_at(trans, iter,
+				BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+		goto out;
+	}
+
+	if (!i)
+		goto out;
+
+	if (fsck_err_on(!S_ISDIR(i->inode.bi_mode),
+			c, dirent_in_non_dir_inode,
+			"dirent in non directory inode type %s:\n%s",
+			bch2_d_type_str(inode_d_type(&i->inode)),
+			(printbuf_reset(&buf),
+			 bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+		ret = bch2_btree_delete_at(trans, iter, 0);
+		goto out;
+	}
+
+	ret = hash_check_key(trans, bch2_dirent_hash_desc, hash_info, iter, k);
+	if (ret < 0)
+		goto err;
+	if (ret) {
+		/* dirent has been deleted */
+		ret = 0;
+		goto out;
+	}
+
+	if (k.k->type != KEY_TYPE_dirent)
+		goto out;
+
+	d = bkey_s_c_to_dirent(k);
+
+	if (d.v->d_type == DT_SUBVOL) {
+		struct bch_inode_unpacked subvol_root;
+		u32 target_subvol = le32_to_cpu(d.v->d_child_subvol);
+		u32 target_snapshot;
+		u64 target_inum;
+
+		ret = __subvol_lookup(trans, target_subvol,
+				      &target_snapshot, &target_inum);
+		if (ret && !bch2_err_matches(ret, ENOENT))
+			goto err;
+
+		if (fsck_err_on(ret, c, dirent_to_missing_subvol,
+				"dirent points to missing subvolume %u",
+				le32_to_cpu(d.v->d_child_subvol))) {
+			ret = __remove_dirent(trans, d.k->p);
+			goto err;
+		}
+
+		ret = __lookup_inode(trans, target_inum,
+				   &subvol_root, &target_snapshot);
+		if (ret && !bch2_err_matches(ret, ENOENT))
+			goto err;
+
+		if (fsck_err_on(ret, c, subvol_to_missing_root,
+				"subvolume %u points to missing subvolume root %llu",
+				target_subvol,
+				target_inum)) {
+			bch_err(c, "repair not implemented yet");
+			ret = -EINVAL;
+			goto err;
+		}
+
+		if (fsck_err_on(subvol_root.bi_subvol != target_subvol,
+				c, subvol_root_wrong_bi_subvol,
+				"subvol root %llu has wrong bi_subvol field: got %u, should be %u",
+				target_inum,
+				subvol_root.bi_subvol, target_subvol)) {
+			subvol_root.bi_subvol = target_subvol;
+			ret = __write_inode(trans, &subvol_root, target_snapshot);
+			if (ret)
+				goto err;
+		}
+
+		ret = check_dirent_target(trans, iter, d, &subvol_root,
+					  target_snapshot);
+		if (ret)
+			goto err;
+	} else {
+		ret = __get_visible_inodes(trans, target, s, le64_to_cpu(d.v->d_inum));
+		if (ret)
+			goto err;
+
+		if (fsck_err_on(!target->inodes.nr,
+				c, dirent_to_missing_inode,
+				"dirent points to missing inode: (equiv %u)\n%s",
+				equiv.snapshot,
+				(printbuf_reset(&buf),
+				 bch2_bkey_val_to_text(&buf, c, k),
+				 buf.buf))) {
+			ret = __remove_dirent(trans, d.k->p);
+			if (ret)
+				goto err;
+		}
+
+		darray_for_each(target->inodes, i) {
+			ret = check_dirent_target(trans, iter, d,
+						  &i->inode, i->snapshot);
+			if (ret)
+				goto err;
+		}
+	}
+
+	if (d.v->d_type == DT_DIR)
+		for_each_visible_inode(c, s, dir, equiv.snapshot, i)
+			i->count++;
+
+out:
+err:
+fsck_err:
+	printbuf_exit(&buf);
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+/*
+ * Walk dirents: verify that they all have a corresponding S_ISDIR inode,
+ * validate d_type
+ */
+int bch2_check_dirents(struct bch_fs *c)
+{
+	struct inode_walker dir = inode_walker_init();
+	struct inode_walker target = inode_walker_init();
+	struct snapshots_seen s;
+	struct bch_hash_info hash_info;
+	struct btree_trans *trans = bch2_trans_get(c);
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret = 0;
+
+	snapshots_seen_init(&s);
+
+	ret = for_each_btree_key_commit(trans, iter, BTREE_ID_dirents,
+			POS(BCACHEFS_ROOT_INO, 0),
+			BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS,
+			k,
+			NULL, NULL,
+			BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
+		check_dirent(trans, &iter, k, &hash_info, &dir, &target, &s));
+
+	bch2_trans_put(trans);
+	snapshots_seen_exit(&s);
+	inode_walker_exit(&dir);
+	inode_walker_exit(&target);
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+static int check_xattr(struct btree_trans *trans, struct btree_iter *iter,
+		       struct bkey_s_c k,
+		       struct bch_hash_info *hash_info,
+		       struct inode_walker *inode)
+{
+	struct bch_fs *c = trans->c;
+	struct inode_walker_entry *i;
+	int ret;
+
+	ret = check_key_has_snapshot(trans, iter, k);
+	if (ret)
+		return ret;
+
+	i = walk_inode(trans, inode, k.k->p, k.k->type == KEY_TYPE_whiteout);
+	ret = PTR_ERR_OR_ZERO(i);
+	if (ret)
+		return ret;
+
+	if (inode->first_this_inode && inode->inodes.nr)
+		*hash_info = bch2_hash_info_init(c, &inode->inodes.data[0].inode);
+	inode->first_this_inode = false;
+
+	if (fsck_err_on(!i, c, xattr_in_missing_inode,
+			"xattr for missing inode %llu",
+			k.k->p.inode))
+		return bch2_btree_delete_at(trans, iter, 0);
+
+	if (!i)
+		return 0;
+
+	ret = hash_check_key(trans, bch2_xattr_hash_desc, hash_info, iter, k);
+fsck_err:
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+/*
+ * Walk xattrs: verify that they all have a corresponding inode
+ */
+int bch2_check_xattrs(struct bch_fs *c)
+{
+	struct inode_walker inode = inode_walker_init();
+	struct bch_hash_info hash_info;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret = 0;
+
+	ret = bch2_trans_run(c,
+		for_each_btree_key_commit(trans, iter, BTREE_ID_xattrs,
+			POS(BCACHEFS_ROOT_INO, 0),
+			BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS,
+			k,
+			NULL, NULL,
+			BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
+		check_xattr(trans, &iter, k, &hash_info, &inode)));
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+static int check_root_trans(struct btree_trans *trans)
+{
+	struct bch_fs *c = trans->c;
+	struct bch_inode_unpacked root_inode;
+	u32 snapshot;
+	u64 inum;
+	int ret;
+
+	ret = __subvol_lookup(trans, BCACHEFS_ROOT_SUBVOL, &snapshot, &inum);
+	if (ret && !bch2_err_matches(ret, ENOENT))
+		return ret;
+
+	if (mustfix_fsck_err_on(ret, c, root_subvol_missing,
+				"root subvol missing")) {
+		struct bkey_i_subvolume root_subvol;
+
+		snapshot	= U32_MAX;
+		inum		= BCACHEFS_ROOT_INO;
+
+		bkey_subvolume_init(&root_subvol.k_i);
+		root_subvol.k.p.offset = BCACHEFS_ROOT_SUBVOL;
+		root_subvol.v.flags	= 0;
+		root_subvol.v.snapshot	= cpu_to_le32(snapshot);
+		root_subvol.v.inode	= cpu_to_le64(inum);
+		ret = commit_do(trans, NULL, NULL,
+				      BTREE_INSERT_NOFAIL|
+				      BTREE_INSERT_LAZY_RW,
+			bch2_btree_insert_trans(trans, BTREE_ID_subvolumes,
+					    &root_subvol.k_i, 0));
+		bch_err_msg(c, ret, "writing root subvol");
+		if (ret)
+			goto err;
+
+	}
+
+	ret = __lookup_inode(trans, BCACHEFS_ROOT_INO, &root_inode, &snapshot);
+	if (ret && !bch2_err_matches(ret, ENOENT))
+		return ret;
+
+	if (mustfix_fsck_err_on(ret, c, root_dir_missing,
+				"root directory missing") ||
+	    mustfix_fsck_err_on(!S_ISDIR(root_inode.bi_mode),
+				c, root_inode_not_dir,
+				"root inode not a directory")) {
+		bch2_inode_init(c, &root_inode, 0, 0, S_IFDIR|0755,
+				0, NULL);
+		root_inode.bi_inum = inum;
+
+		ret = __write_inode(trans, &root_inode, snapshot);
+		bch_err_msg(c, ret, "writing root inode");
+	}
+err:
+fsck_err:
+	return ret;
+}
+
+/* Get root directory, create if it doesn't exist: */
+int bch2_check_root(struct bch_fs *c)
+{
+	int ret;
+
+	ret = bch2_trans_do(c, NULL, NULL,
+			     BTREE_INSERT_NOFAIL|
+			     BTREE_INSERT_LAZY_RW,
+		check_root_trans(trans));
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+struct pathbuf_entry {
+	u64	inum;
+	u32	snapshot;
+};
+
+typedef DARRAY(struct pathbuf_entry) pathbuf;
+
+static bool path_is_dup(pathbuf *p, u64 inum, u32 snapshot)
+{
+	struct pathbuf_entry *i;
+
+	darray_for_each(*p, i)
+		if (i->inum	== inum &&
+		    i->snapshot	== snapshot)
+			return true;
+
+	return false;
+}
+
+static int path_down(struct bch_fs *c, pathbuf *p,
+		     u64 inum, u32 snapshot)
+{
+	int ret = darray_push(p, ((struct pathbuf_entry) {
+		.inum		= inum,
+		.snapshot	= snapshot,
+	}));
+
+	if (ret)
+		bch_err(c, "fsck: error allocating memory for pathbuf, size %zu",
+			p->size);
+	return ret;
+}
+
+/*
+ * Check that a given inode is reachable from the root:
+ *
+ * XXX: we should also be verifying that inodes are in the right subvolumes
+ */
+static int check_path(struct btree_trans *trans,
+		      pathbuf *p,
+		      struct bch_inode_unpacked *inode,
+		      u32 snapshot)
+{
+	struct bch_fs *c = trans->c;
+	int ret = 0;
+
+	snapshot = bch2_snapshot_equiv(c, snapshot);
+	p->nr = 0;
+
+	while (!(inode->bi_inum == BCACHEFS_ROOT_INO &&
+		 inode->bi_subvol == BCACHEFS_ROOT_SUBVOL)) {
+		struct btree_iter dirent_iter;
+		struct bkey_s_c_dirent d;
+		u32 parent_snapshot = snapshot;
+
+		if (inode->bi_subvol) {
+			u64 inum;
+
+			ret = subvol_lookup(trans, inode->bi_parent_subvol,
+					    &parent_snapshot, &inum);
+			if (ret)
+				break;
+		}
+
+		ret = lockrestart_do(trans,
+			PTR_ERR_OR_ZERO((d = dirent_get_by_pos(trans, &dirent_iter,
+					  SPOS(inode->bi_dir, inode->bi_dir_offset,
+					       parent_snapshot))).k));
+		if (ret && !bch2_err_matches(ret, ENOENT))
+			break;
+
+		if (!ret && !dirent_points_to_inode(d, inode)) {
+			bch2_trans_iter_exit(trans, &dirent_iter);
+			ret = -BCH_ERR_ENOENT_dirent_doesnt_match_inode;
+		}
+
+		if (bch2_err_matches(ret, ENOENT)) {
+			if (fsck_err(c,  inode_unreachable,
+				     "unreachable inode %llu:%u, type %s nlink %u backptr %llu:%llu",
+				     inode->bi_inum, snapshot,
+				     bch2_d_type_str(inode_d_type(inode)),
+				     inode->bi_nlink,
+				     inode->bi_dir,
+				     inode->bi_dir_offset))
+				ret = reattach_inode(trans, inode, snapshot);
+			break;
+		}
+
+		bch2_trans_iter_exit(trans, &dirent_iter);
+
+		if (!S_ISDIR(inode->bi_mode))
+			break;
+
+		ret = path_down(c, p, inode->bi_inum, snapshot);
+		if (ret) {
+			bch_err(c, "memory allocation failure");
+			return ret;
+		}
+
+		snapshot = parent_snapshot;
+
+		ret = lookup_inode(trans, inode->bi_dir, inode, &snapshot);
+		if (ret) {
+			/* Should have been caught in dirents pass */
+			bch_err(c, "error looking up parent directory: %i", ret);
+			break;
+		}
+
+		if (path_is_dup(p, inode->bi_inum, snapshot)) {
+			struct pathbuf_entry *i;
+
+			/* XXX print path */
+			bch_err(c, "directory structure loop");
+
+			darray_for_each(*p, i)
+				pr_err("%llu:%u", i->inum, i->snapshot);
+			pr_err("%llu:%u", inode->bi_inum, snapshot);
+
+			if (!fsck_err(c, dir_loop,
+				      "directory structure loop"))
+				return 0;
+
+			ret = commit_do(trans, NULL, NULL,
+					      BTREE_INSERT_NOFAIL|
+					      BTREE_INSERT_LAZY_RW,
+					remove_backpointer(trans, inode));
+			if (ret) {
+				bch_err(c, "error removing dirent: %i", ret);
+				break;
+			}
+
+			ret = reattach_inode(trans, inode, snapshot);
+		}
+	}
+fsck_err:
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+/*
+ * Check for unreachable inodes, as well as loops in the directory structure:
+ * After bch2_check_dirents(), if an inode backpointer doesn't exist that means it's
+ * unreachable:
+ */
+int bch2_check_directory_structure(struct bch_fs *c)
+{
+	struct btree_trans *trans = bch2_trans_get(c);
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bch_inode_unpacked u;
+	pathbuf path = { 0, };
+	int ret;
+
+	for_each_btree_key(trans, iter, BTREE_ID_inodes, POS_MIN,
+			   BTREE_ITER_INTENT|
+			   BTREE_ITER_PREFETCH|
+			   BTREE_ITER_ALL_SNAPSHOTS, k, ret) {
+		if (!bkey_is_inode(k.k))
+			continue;
+
+		ret = bch2_inode_unpack(k, &u);
+		if (ret) {
+			/* Should have been caught earlier in fsck: */
+			bch_err(c, "error unpacking inode %llu: %i", k.k->p.offset, ret);
+			break;
+		}
+
+		if (u.bi_flags & BCH_INODE_unlinked)
+			continue;
+
+		ret = check_path(trans, &path, &u, iter.pos.snapshot);
+		if (ret)
+			break;
+	}
+	bch2_trans_iter_exit(trans, &iter);
+	bch2_trans_put(trans);
+	darray_exit(&path);
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+struct nlink_table {
+	size_t		nr;
+	size_t		size;
+
+	struct nlink {
+		u64	inum;
+		u32	snapshot;
+		u32	count;
+	}		*d;
+};
+
+static int add_nlink(struct bch_fs *c, struct nlink_table *t,
+		     u64 inum, u32 snapshot)
+{
+	if (t->nr == t->size) {
+		size_t new_size = max_t(size_t, 128UL, t->size * 2);
+		void *d = kvmalloc_array(new_size, sizeof(t->d[0]), GFP_KERNEL);
+
+		if (!d) {
+			bch_err(c, "fsck: error allocating memory for nlink_table, size %zu",
+				new_size);
+			return -BCH_ERR_ENOMEM_fsck_add_nlink;
+		}
+
+		if (t->d)
+			memcpy(d, t->d, t->size * sizeof(t->d[0]));
+		kvfree(t->d);
+
+		t->d = d;
+		t->size = new_size;
+	}
+
+
+	t->d[t->nr++] = (struct nlink) {
+		.inum		= inum,
+		.snapshot	= snapshot,
+	};
+
+	return 0;
+}
+
+static int nlink_cmp(const void *_l, const void *_r)
+{
+	const struct nlink *l = _l;
+	const struct nlink *r = _r;
+
+	return cmp_int(l->inum, r->inum);
+}
+
+static void inc_link(struct bch_fs *c, struct snapshots_seen *s,
+		     struct nlink_table *links,
+		     u64 range_start, u64 range_end, u64 inum, u32 snapshot)
+{
+	struct nlink *link, key = {
+		.inum = inum, .snapshot = U32_MAX,
+	};
+
+	if (inum < range_start || inum >= range_end)
+		return;
+
+	link = __inline_bsearch(&key, links->d, links->nr,
+				sizeof(links->d[0]), nlink_cmp);
+	if (!link)
+		return;
+
+	while (link > links->d && link[0].inum == link[-1].inum)
+		--link;
+
+	for (; link < links->d + links->nr && link->inum == inum; link++)
+		if (ref_visible(c, s, snapshot, link->snapshot)) {
+			link->count++;
+			if (link->snapshot >= snapshot)
+				break;
+		}
+}
+
+noinline_for_stack
+static int check_nlinks_find_hardlinks(struct bch_fs *c,
+				       struct nlink_table *t,
+				       u64 start, u64 *end)
+{
+	struct btree_trans *trans = bch2_trans_get(c);
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bch_inode_unpacked u;
+	int ret = 0;
+
+	for_each_btree_key(trans, iter, BTREE_ID_inodes,
+			   POS(0, start),
+			   BTREE_ITER_INTENT|
+			   BTREE_ITER_PREFETCH|
+			   BTREE_ITER_ALL_SNAPSHOTS, k, ret) {
+		if (!bkey_is_inode(k.k))
+			continue;
+
+		/* Should never fail, checked by bch2_inode_invalid: */
+		BUG_ON(bch2_inode_unpack(k, &u));
+
+		/*
+		 * Backpointer and directory structure checks are sufficient for
+		 * directories, since they can't have hardlinks:
+		 */
+		if (S_ISDIR(u.bi_mode))
+			continue;
+
+		if (!u.bi_nlink)
+			continue;
+
+		ret = add_nlink(c, t, k.k->p.offset, k.k->p.snapshot);
+		if (ret) {
+			*end = k.k->p.offset;
+			ret = 0;
+			break;
+		}
+
+	}
+	bch2_trans_iter_exit(trans, &iter);
+	bch2_trans_put(trans);
+
+	if (ret)
+		bch_err(c, "error in fsck: btree error %i while walking inodes", ret);
+
+	return ret;
+}
+
+noinline_for_stack
+static int check_nlinks_walk_dirents(struct bch_fs *c, struct nlink_table *links,
+				     u64 range_start, u64 range_end)
+{
+	struct btree_trans *trans = bch2_trans_get(c);
+	struct snapshots_seen s;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bkey_s_c_dirent d;
+	int ret;
+
+	snapshots_seen_init(&s);
+
+	for_each_btree_key(trans, iter, BTREE_ID_dirents, POS_MIN,
+			   BTREE_ITER_INTENT|
+			   BTREE_ITER_PREFETCH|
+			   BTREE_ITER_ALL_SNAPSHOTS, k, ret) {
+		ret = snapshots_seen_update(c, &s, iter.btree_id, k.k->p);
+		if (ret)
+			break;
+
+		switch (k.k->type) {
+		case KEY_TYPE_dirent:
+			d = bkey_s_c_to_dirent(k);
+
+			if (d.v->d_type != DT_DIR &&
+			    d.v->d_type != DT_SUBVOL)
+				inc_link(c, &s, links, range_start, range_end,
+					 le64_to_cpu(d.v->d_inum),
+					 bch2_snapshot_equiv(c, d.k->p.snapshot));
+			break;
+		}
+	}
+	bch2_trans_iter_exit(trans, &iter);
+
+	if (ret)
+		bch_err(c, "error in fsck: btree error %i while walking dirents", ret);
+
+	bch2_trans_put(trans);
+	snapshots_seen_exit(&s);
+	return ret;
+}
+
+static int check_nlinks_update_inode(struct btree_trans *trans, struct btree_iter *iter,
+				     struct bkey_s_c k,
+				     struct nlink_table *links,
+				     size_t *idx, u64 range_end)
+{
+	struct bch_fs *c = trans->c;
+	struct bch_inode_unpacked u;
+	struct nlink *link = &links->d[*idx];
+	int ret = 0;
+
+	if (k.k->p.offset >= range_end)
+		return 1;
+
+	if (!bkey_is_inode(k.k))
+		return 0;
+
+	BUG_ON(bch2_inode_unpack(k, &u));
+
+	if (S_ISDIR(u.bi_mode))
+		return 0;
+
+	if (!u.bi_nlink)
+		return 0;
+
+	while ((cmp_int(link->inum, k.k->p.offset) ?:
+		cmp_int(link->snapshot, k.k->p.snapshot)) < 0) {
+		BUG_ON(*idx == links->nr);
+		link = &links->d[++*idx];
+	}
+
+	if (fsck_err_on(bch2_inode_nlink_get(&u) != link->count,
+			c, inode_wrong_nlink,
+			"inode %llu type %s has wrong i_nlink (%u, should be %u)",
+			u.bi_inum, bch2_d_types[mode_to_type(u.bi_mode)],
+			bch2_inode_nlink_get(&u), link->count)) {
+		bch2_inode_nlink_set(&u, link->count);
+		ret = __write_inode(trans, &u, k.k->p.snapshot);
+	}
+fsck_err:
+	return ret;
+}
+
+noinline_for_stack
+static int check_nlinks_update_hardlinks(struct bch_fs *c,
+			       struct nlink_table *links,
+			       u64 range_start, u64 range_end)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	size_t idx = 0;
+	int ret = 0;
+
+	ret = bch2_trans_run(c,
+		for_each_btree_key_commit(trans, iter, BTREE_ID_inodes,
+				POS(0, range_start),
+				BTREE_ITER_INTENT|BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS, k,
+				NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
+			check_nlinks_update_inode(trans, &iter, k, links, &idx, range_end)));
+	if (ret < 0) {
+		bch_err(c, "error in fsck: btree error %i while walking inodes", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+int bch2_check_nlinks(struct bch_fs *c)
+{
+	struct nlink_table links = { 0 };
+	u64 this_iter_range_start, next_iter_range_start = 0;
+	int ret = 0;
+
+	do {
+		this_iter_range_start = next_iter_range_start;
+		next_iter_range_start = U64_MAX;
+
+		ret = check_nlinks_find_hardlinks(c, &links,
+						  this_iter_range_start,
+						  &next_iter_range_start);
+
+		ret = check_nlinks_walk_dirents(c, &links,
+					  this_iter_range_start,
+					  next_iter_range_start);
+		if (ret)
+			break;
+
+		ret = check_nlinks_update_hardlinks(c, &links,
+					 this_iter_range_start,
+					 next_iter_range_start);
+		if (ret)
+			break;
+
+		links.nr = 0;
+	} while (next_iter_range_start != U64_MAX);
+
+	kvfree(links.d);
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+static int fix_reflink_p_key(struct btree_trans *trans, struct btree_iter *iter,
+			     struct bkey_s_c k)
+{
+	struct bkey_s_c_reflink_p p;
+	struct bkey_i_reflink_p *u;
+	int ret;
+
+	if (k.k->type != KEY_TYPE_reflink_p)
+		return 0;
+
+	p = bkey_s_c_to_reflink_p(k);
+
+	if (!p.v->front_pad && !p.v->back_pad)
+		return 0;
+
+	u = bch2_trans_kmalloc(trans, sizeof(*u));
+	ret = PTR_ERR_OR_ZERO(u);
+	if (ret)
+		return ret;
+
+	bkey_reassemble(&u->k_i, k);
+	u->v.front_pad	= 0;
+	u->v.back_pad	= 0;
+
+	return bch2_trans_update(trans, iter, &u->k_i, BTREE_TRIGGER_NORUN);
+}
+
+int bch2_fix_reflink_p(struct bch_fs *c)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	if (c->sb.version >= bcachefs_metadata_version_reflink_p_fix)
+		return 0;
+
+	ret = bch2_trans_run(c,
+		for_each_btree_key_commit(trans, iter,
+				BTREE_ID_extents, POS_MIN,
+				BTREE_ITER_INTENT|BTREE_ITER_PREFETCH|
+				BTREE_ITER_ALL_SNAPSHOTS, k,
+				NULL, NULL, BTREE_INSERT_NOFAIL|BTREE_INSERT_LAZY_RW,
+			fix_reflink_p_key(trans, &iter, k)));
+	bch_err_fn(c, ret);
+	return ret;
+}