Update bcachefs sources to a8115093df bcachefs: Fix divide by zero in rebalance_work()

43 files changed, 1484 insertions, 1251 deletions

diff --git a/.bcachefs_revision b/.bcachefs_revision
index 5fb87b74..18ed8bfc 100644
--- a/.bcachefs_revision
+++ b/.bcachefs_revision
@@ -1 +1 @@
-b0788c47d97935856809bd1357423978dbfcdf9f
+a8115093df3e08c3e4bf6dab222e1cac132fff69
diff --git a/Makefile b/Makefile
index 2556695d..a221e66d 100644
--- a/Makefile
+++ b/Makefile
@@ -199,10 +199,6 @@ update-bcachefs-sources:
 	git add include/linux/xxhash.h
 	cp $(LINUX_DIR)/lib/xxhash.c linux/
 	git add linux/xxhash.c
-	cp $(LINUX_DIR)/kernel/locking/six.c linux/
-	git add linux/six.c
-	cp $(LINUX_DIR)/include/linux/six.h include/linux/
-	git add include/linux/six.h
 	cp $(LINUX_DIR)/include/linux/list_nulls.h include/linux/
 	git add include/linux/list_nulls.h
 	cp $(LINUX_DIR)/include/linux/poison.h include/linux/
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c5c8e3ac..825eea5c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -107,7 +107,12 @@ extern __thread struct task_struct *current;
 #define set_current_state(state_value)			\
 	smp_store_mb(current->state, (state_value))
 
-#define get_task_struct(tsk) do { atomic_inc(&(tsk)->usage); } while(0)
+static inline struct task_struct *get_task_struct(struct task_struct *task)
+{
+	atomic_inc(&task->usage);
+	return task;
+
+}
 
 extern void __put_task_struct(struct task_struct *t);
 
diff --git a/libbcachefs/alloc_foreground.c b/libbcachefs/alloc_foreground.c
index 1f4c5b38..e02749dd 100644
--- a/libbcachefs/alloc_foreground.c
+++ b/libbcachefs/alloc_foreground.c
@@ -989,7 +989,6 @@ retry_blocking:
 			cl = _cl;
 			goto retry_blocking;
 		}
-
 	}
 
 	return ret;
@@ -1031,6 +1030,16 @@ static int open_bucket_add_buckets(struct btree_trans *trans,
 	return ret < 0 ? ret : 0;
 }
 
+/**
+ * should_drop_bucket - check if this is open_bucket should go away
+ * @ca:		if set, we're killing buckets for a particular device
+ * @ec:		if true, we're shutting down erasure coding and killing all ec
+ *		open_buckets
+ *		otherwise, return true
+ *
+ * We're killing open_buckets because we're shutting down a device, erasure
+ * coding, or the entire filesystem - check if this open_bucket matches:
+ */
 static bool should_drop_bucket(struct open_bucket *ob, struct bch_fs *c,
 			       struct bch_dev *ca, bool ec)
 {
@@ -1516,25 +1525,47 @@ static const char * const bch2_write_point_states[] = {
 	NULL
 };
 
+static void bch2_write_point_to_text(struct printbuf *out, struct bch_fs *c,
+				     struct write_point *wp)
+{
+	struct open_bucket *ob;
+	unsigned i;
+
+	prt_printf(out, "%lu: ", wp->write_point);
+	prt_human_readable_u64(out, wp->sectors_allocated);
+
+	prt_printf(out, " last wrote: ");
+	bch2_pr_time_units(out, sched_clock() - wp->last_used);
+
+	for (i = 0; i < WRITE_POINT_STATE_NR; i++) {
+		prt_printf(out, " %s: ", bch2_write_point_states[i]);
+		bch2_pr_time_units(out, wp->time[i]);
+	}
+
+	prt_newline(out);
+
+	printbuf_indent_add(out, 2);
+	open_bucket_for_each(c, &wp->ptrs, ob, i)
+		bch2_open_bucket_to_text(out, c, ob);
+	printbuf_indent_sub(out, 2);
+}
+
 void bch2_write_points_to_text(struct printbuf *out, struct bch_fs *c)
 {
 	struct write_point *wp;
-	unsigned i;
 
+	prt_str(out, "Foreground write points\n");
 	for (wp = c->write_points;
 	     wp < c->write_points + ARRAY_SIZE(c->write_points);
-	     wp++) {
-		prt_printf(out, "%lu: ", wp->write_point);
-		prt_human_readable_u64(out, wp->sectors_allocated);
+	     wp++)
+		bch2_write_point_to_text(out, c, wp);
 
-		prt_printf(out, " last wrote: ");
-		bch2_pr_time_units(out, sched_clock() - wp->last_used);
+	prt_str(out, "Copygc write point\n");
+	bch2_write_point_to_text(out, c, &c->copygc_write_point);
 
-		for (i = 0; i < WRITE_POINT_STATE_NR; i++) {
-			prt_printf(out, " %s: ", bch2_write_point_states[i]);
-			bch2_pr_time_units(out, wp->time[i]);
-		}
+	prt_str(out, "Rebalance write point\n");
+	bch2_write_point_to_text(out, c, &c->rebalance_write_point);
 
-		prt_newline(out);
-	}
+	prt_str(out, "Btree write point\n");
+	bch2_write_point_to_text(out, c, &c->btree_write_point);
 }
diff --git a/libbcachefs/bcachefs_format.h b/libbcachefs/bcachefs_format.h
index 5ec218ee..20e96daf 100644
--- a/libbcachefs/bcachefs_format.h
+++ b/libbcachefs/bcachefs_format.h
@@ -916,9 +916,7 @@ struct bch_dirent {
 #define DT_SUBVOL	16
 #define BCH_DT_MAX	17
 
-#define BCH_NAME_MAX	((unsigned) (U8_MAX * sizeof(__u64) -		\
-			 sizeof(struct bkey) -				\
-			 offsetof(struct bch_dirent, d_name)))
+#define BCH_NAME_MAX	512
 
 /* Xattrs */
 
@@ -1126,6 +1124,11 @@ struct bch_subvolume {
 	__le32			flags;
 	__le32			snapshot;
 	__le64			inode;
+	/*
+	 * Snapshot subvolumes form a tree, separate from the snapshot nodes
+	 * tree - if this subvolume is a snapshot, this is the ID of the
+	 * subvolume it was created from:
+	 */
 	__le32			parent;
 	__le32			pad;
 	bch_le128		otime;
diff --git a/libbcachefs/bkey.c b/libbcachefs/bkey.c
index d6960e25..0a5bfe6e 100644
--- a/libbcachefs/bkey.c
+++ b/libbcachefs/bkey.c
@@ -591,8 +591,10 @@ struct bkey_format bch2_bkey_format_done(struct bkey_format_state *s)
 
 	/* allow for extent merging: */
 	if (ret.bits_per_field[BKEY_FIELD_SIZE]) {
-		ret.bits_per_field[BKEY_FIELD_SIZE] += 4;
-		bits += 4;
+		unsigned b = min(4U, 32U - ret.bits_per_field[BKEY_FIELD_SIZE]);
+
+		ret.bits_per_field[BKEY_FIELD_SIZE] += b;
+		bits += b;
 	}
 
 	ret.key_u64s = DIV_ROUND_UP(bits, 64);
diff --git a/libbcachefs/bkey_methods.c b/libbcachefs/bkey_methods.c
index 90557f4c..6547142d 100644
--- a/libbcachefs/bkey_methods.c
+++ b/libbcachefs/bkey_methods.c
@@ -13,6 +13,7 @@
 #include "lru.h"
 #include "quota.h"
 #include "reflink.h"
+#include "snapshot.h"
 #include "subvolume.h"
 #include "xattr.h"
 
diff --git a/libbcachefs/btree_iter.c b/libbcachefs/btree_iter.c
index 9b6807f6..5216d339 100644
--- a/libbcachefs/btree_iter.c
+++ b/libbcachefs/btree_iter.c
@@ -14,7 +14,7 @@
 #include "extents.h"
 #include "journal.h"
 #include "replicas.h"
-#include "subvolume.h"
+#include "snapshot.h"
 #include "trace.h"
 
 #include <linux/random.h>
@@ -2898,12 +2898,14 @@ static void bch2_trans_alloc_paths(struct btree_trans *trans, struct bch_fs *c)
 #ifdef __KERNEL__
 	p = this_cpu_xchg(c->btree_paths_bufs->path, NULL);
 #endif
-	if (!p)
+	if (!p) {
 		p = mempool_alloc(&trans->c->btree_paths_pool, GFP_NOFS);
-	/*
-	 * paths need to be zeroed, bch2_check_for_deadlock looks at paths in
-	 * other threads
-	 */
+		/*
+		 * paths need to be zeroed, bch2_check_for_deadlock looks at
+		 * paths in other threads
+		 */
+		memset(p, 0, paths_bytes);
+	}
 
 	trans->paths		= p; p += paths_bytes;
 	trans->updates		= p; p += updates_bytes;
diff --git a/libbcachefs/btree_locking.h b/libbcachefs/btree_locking.h
index ce3c7d9f..22e2cd39 100644
--- a/libbcachefs/btree_locking.h
+++ b/libbcachefs/btree_locking.h
@@ -10,9 +10,8 @@
  * updating the iterator state
  */
 
-#include <linux/six.h>
-
 #include "btree_iter.h"
+#include "six.h"
 
 void bch2_btree_lock_init(struct btree_bkey_cached_common *, enum six_lock_init_flags);
 
diff --git a/libbcachefs/btree_trans_commit.c b/libbcachefs/btree_trans_commit.c
index 78a09aa0..83cc7f64 100644
--- a/libbcachefs/btree_trans_commit.c
+++ b/libbcachefs/btree_trans_commit.c
@@ -14,7 +14,7 @@
 #include "journal.h"
 #include "journal_reclaim.h"
 #include "replicas.h"
-#include "subvolume.h"
+#include "snapshot.h"
 
 #include <linux/prefetch.h>
 
diff --git a/libbcachefs/btree_types.h b/libbcachefs/btree_types.h
index 6b6333df..71ad3893 100644
--- a/libbcachefs/btree_types.h
+++ b/libbcachefs/btree_types.h
@@ -4,7 +4,6 @@
 
 #include <linux/list.h>
 #include <linux/rhashtable.h>
-#include <linux/six.h>
 
 //#include "bkey_methods.h"
 #include "buckets_types.h"
@@ -12,6 +11,7 @@
 #include "errcode.h"
 #include "journal_types.h"
 #include "replicas_types.h"
+#include "six.h"
 
 struct open_bucket;
 struct btree_update;
diff --git a/libbcachefs/btree_update.c b/libbcachefs/btree_update.c
index 612fba60..a7fa2072 100644
--- a/libbcachefs/btree_update.c
+++ b/libbcachefs/btree_update.c
@@ -11,7 +11,7 @@
 #include "error.h"
 #include "extents.h"
 #include "keylist.h"
-#include "subvolume.h"
+#include "snapshot.h"
 #include "trace.h"
 
 static inline int btree_insert_entry_cmp(const struct btree_insert_entry *l,
diff --git a/libbcachefs/btree_update_interior.c b/libbcachefs/btree_update_interior.c
index 986dd541..c741150e 100644
--- a/libbcachefs/btree_update_interior.c
+++ b/libbcachefs/btree_update_interior.c
@@ -2385,7 +2385,7 @@ void bch2_btree_updates_to_text(struct printbuf *out, struct bch_fs *c)
 		       as,
 		       as->mode,
 		       as->nodes_written,
-		       atomic_read(&as->cl.remaining) & CLOSURE_REMAINING_MASK,
+		       closure_nr_remaining(&as->cl),
 		       as->journal.seq);
 	mutex_unlock(&c->btree_interior_update_lock);
 }
diff --git a/libbcachefs/data_update.c b/libbcachefs/data_update.c
index cfc62446..81518f20 100644
--- a/libbcachefs/data_update.c
+++ b/libbcachefs/data_update.c
@@ -415,7 +415,7 @@ void bch2_update_unwritten_extent(struct btree_trans *trans,
 			break;
 	}
 
-	if ((atomic_read(&cl.remaining) & CLOSURE_REMAINING_MASK) != 1) {
+	if (closure_nr_remaining(&cl) != 1) {
 		bch2_trans_unlock(trans);
 		closure_sync(&cl);
 	}
diff --git a/libbcachefs/dirent.c b/libbcachefs/dirent.c
index 065ea59e..a7559ab0 100644
--- a/libbcachefs/dirent.c
+++ b/libbcachefs/dirent.c
@@ -13,12 +13,25 @@
 
 #include <linux/dcache.h>
 
-unsigned bch2_dirent_name_bytes(struct bkey_s_c_dirent d)
+static unsigned bch2_dirent_name_bytes(struct bkey_s_c_dirent d)
 {
-	unsigned len = bkey_val_bytes(d.k) -
-		offsetof(struct bch_dirent, d_name);
+	unsigned bkey_u64s = bkey_val_u64s(d.k);
+	unsigned bkey_bytes = bkey_u64s * sizeof(u64);
+	u64 last_u64 = ((u64*)d.v)[bkey_u64s - 1];
+#if CPU_BIG_ENDIAN
+	unsigned trailing_nuls = last_u64 ? __builtin_ctzll(last_u64) / 8 : 64 / 8;
+#else
+	unsigned trailing_nuls = last_u64 ? __builtin_clzll(last_u64) / 8 : 64 / 8;
+#endif
+
+	return bkey_bytes -
+		offsetof(struct bch_dirent, d_name) -
+		trailing_nuls;
+}
 
-	return strnlen(d.v->d_name, len);
+struct qstr bch2_dirent_get_name(struct bkey_s_c_dirent d)
+{
+	return (struct qstr) QSTR_INIT(d.v->d_name, bch2_dirent_name_bytes(d));
 }
 
 static u64 bch2_dirent_hash(const struct bch_hash_info *info,
@@ -41,7 +54,7 @@ static u64 dirent_hash_key(const struct bch_hash_info *info, const void *key)
 static u64 dirent_hash_bkey(const struct bch_hash_info *info, struct bkey_s_c k)
 {
 	struct bkey_s_c_dirent d = bkey_s_c_to_dirent(k);
-	struct qstr name = QSTR_INIT(d.v->d_name, bch2_dirent_name_bytes(d));
+	struct qstr name = bch2_dirent_get_name(d);
 
 	return bch2_dirent_hash(info, &name);
 }
@@ -49,20 +62,20 @@ static u64 dirent_hash_bkey(const struct bch_hash_info *info, struct bkey_s_c k)
 static bool dirent_cmp_key(struct bkey_s_c _l, const void *_r)
 {
 	struct bkey_s_c_dirent l = bkey_s_c_to_dirent(_l);
-	int len = bch2_dirent_name_bytes(l);
-	const struct qstr *r = _r;
+	const struct qstr l_name = bch2_dirent_get_name(l);
+	const struct qstr *r_name = _r;
 
-	return len - r->len ?: memcmp(l.v->d_name, r->name, len);
+	return l_name.len - r_name->len ?: memcmp(l_name.name, r_name->name, l_name.len);
 }
 
 static bool dirent_cmp_bkey(struct bkey_s_c _l, struct bkey_s_c _r)
 {
 	struct bkey_s_c_dirent l = bkey_s_c_to_dirent(_l);
 	struct bkey_s_c_dirent r = bkey_s_c_to_dirent(_r);
-	int l_len = bch2_dirent_name_bytes(l);
-	int r_len = bch2_dirent_name_bytes(r);
+	const struct qstr l_name = bch2_dirent_get_name(l);
+	const struct qstr r_name = bch2_dirent_get_name(r);
 
-	return l_len - r_len ?: memcmp(l.v->d_name, r.v->d_name, l_len);
+	return l_name.len - r_name.len ?: memcmp(l_name.name, r_name.name, l_name.len);
 }
 
 static bool dirent_is_visible(subvol_inum inum, struct bkey_s_c k)
@@ -89,37 +102,45 @@ int bch2_dirent_invalid(const struct bch_fs *c, struct bkey_s_c k,
 			struct printbuf *err)
 {
 	struct bkey_s_c_dirent d = bkey_s_c_to_dirent(k);
-	unsigned len;
+	struct qstr d_name = bch2_dirent_get_name(d);
 
-	len = bch2_dirent_name_bytes(d);
-	if (!len) {
+	if (!d_name.len) {
 		prt_printf(err, "empty name");
 		return -BCH_ERR_invalid_bkey;
 	}
 
-	if (bkey_val_u64s(k.k) > dirent_val_u64s(len)) {
+	if (bkey_val_u64s(k.k) > dirent_val_u64s(d_name.len)) {
 		prt_printf(err, "value too big (%zu > %u)",
-		       bkey_val_u64s(k.k), dirent_val_u64s(len));
+		       bkey_val_u64s(k.k), dirent_val_u64s(d_name.len));
 		return -BCH_ERR_invalid_bkey;
 	}
 
-	if (len > BCH_NAME_MAX) {
+	/*
+	 * Check new keys don't exceed the max length
+	 * (older keys may be larger.)
+	 */
+	if ((flags & BKEY_INVALID_COMMIT) && d_name.len > BCH_NAME_MAX) {
 		prt_printf(err, "dirent name too big (%u > %u)",
-		       len, BCH_NAME_MAX);
+		       d_name.len, BCH_NAME_MAX);
 		return -BCH_ERR_invalid_bkey;
 	}
 
-	if (len == 1 && !memcmp(d.v->d_name, ".", 1)) {
+	if (d_name.len != strnlen(d_name.name, d_name.len)) {
+		prt_printf(err, "dirent has stray data after name's NUL");
+		return -BCH_ERR_invalid_bkey;
+	}
+
+	if (d_name.len == 1 && !memcmp(d_name.name, ".", 1)) {
 		prt_printf(err, "invalid name");
 		return -BCH_ERR_invalid_bkey;
 	}
 
-	if (len == 2 && !memcmp(d.v->d_name, "..", 2)) {
+	if (d_name.len == 2 && !memcmp(d_name.name, "..", 2)) {
 		prt_printf(err, "invalid name");
 		return -BCH_ERR_invalid_bkey;
 	}
 
-	if (memchr(d.v->d_name, '/', len)) {
+	if (memchr(d_name.name, '/', d_name.len)) {
 		prt_printf(err, "invalid name");
 		return -BCH_ERR_invalid_bkey;
 	}
@@ -137,10 +158,11 @@ void bch2_dirent_to_text(struct printbuf *out, struct bch_fs *c,
 			 struct bkey_s_c k)
 {
 	struct bkey_s_c_dirent d = bkey_s_c_to_dirent(k);
+	struct qstr d_name = bch2_dirent_get_name(d);
 
 	prt_printf(out, "%.*s -> %llu type %s",
-	       bch2_dirent_name_bytes(d),
-	       d.v->d_name,
+	       d_name.len,
+	       d_name.name,
 	       d.v->d_type != DT_SUBVOL
 	       ? le64_to_cpu(d.v->d_inum)
 	       : le32_to_cpu(d.v->d_child_subvol),
@@ -507,6 +529,7 @@ int bch2_readdir(struct bch_fs *c, subvol_inum inum, struct dir_context *ctx)
 	subvol_inum target;
 	u32 snapshot;
 	struct bkey_buf sk;
+	struct qstr name;
 	int ret;
 
 	bch2_bkey_buf_init(&sk);
@@ -537,9 +560,11 @@ retry:
 		dirent = bkey_i_to_s_c_dirent(sk.k);
 		bch2_trans_unlock(&trans);
 
+		name = bch2_dirent_get_name(dirent);
+
 		ctx->pos = dirent.k->p.offset;
-		if (!dir_emit(ctx, dirent.v->d_name,
-			      bch2_dirent_name_bytes(dirent),
+		if (!dir_emit(ctx, name.name,
+			      name.len,
 			      target.inum,
 			      vfs_d_type(dirent.v->d_type)))
 			break;
diff --git a/libbcachefs/dirent.h b/libbcachefs/dirent.h
index b42f4a13..e9fa1df3 100644
--- a/libbcachefs/dirent.h
+++ b/libbcachefs/dirent.h
@@ -24,7 +24,7 @@ struct bch_fs;
 struct bch_hash_info;
 struct bch_inode_info;
 
-unsigned bch2_dirent_name_bytes(struct bkey_s_c_dirent);
+struct qstr bch2_dirent_get_name(struct bkey_s_c_dirent d);
 
 static inline unsigned dirent_val_u64s(unsigned len)
 {
diff --git a/libbcachefs/extents.c b/libbcachefs/extents.c
index d7f74db4..1b25f84e 100644
--- a/libbcachefs/extents.c
+++ b/libbcachefs/extents.c
@@ -1059,6 +1059,7 @@ void bch2_bkey_ptrs_to_text(struct printbuf *out, struct bch_fs *c,
 
 static int extent_ptr_invalid(const struct bch_fs *c,
 			      struct bkey_s_c k,
+			      enum bkey_invalid_flags flags,
 			      const struct bch_extent_ptr *ptr,
 			      unsigned size_ondisk,
 			      bool metadata,
@@ -1071,6 +1072,14 @@ static int extent_ptr_invalid(const struct bch_fs *c,
 	struct bch_dev *ca;
 
 	if (!bch2_dev_exists2(c, ptr->dev)) {
+		/*
+		 * If we're in the write path this key might have already been
+		 * overwritten, and we could be seeing a device that doesn't
+		 * exist anymore due to racing with device removal:
+		 */
+		if (flags & BKEY_INVALID_WRITE)
+			return 0;
+
 		prt_printf(err, "pointer to invalid device (%u)", ptr->dev);
 		return -BCH_ERR_invalid_bkey;
 	}
@@ -1136,8 +1145,8 @@ int bch2_bkey_ptrs_invalid(const struct bch_fs *c, struct bkey_s_c k,
 
 		switch (extent_entry_type(entry)) {
 		case BCH_EXTENT_ENTRY_ptr:
-			ret = extent_ptr_invalid(c, k, &entry->ptr, size_ondisk,
-						 false, err);
+			ret = extent_ptr_invalid(c, k, flags, &entry->ptr,
+						 size_ondisk, false, err);
 			if (ret)
 				return ret;
 
diff --git a/libbcachefs/fs-io-buffered.c b/libbcachefs/fs-io-buffered.c
index b6d05019..cbfb5b21 100644
--- a/libbcachefs/fs-io-buffered.c
+++ b/libbcachefs/fs-io-buffered.c
@@ -909,6 +909,7 @@ static int __bch2_buffered_write(struct bch_inode_info *inode,
 		if (!folio_test_uptodate(f) &&
 		    f_copied != folio_size(f) &&
 		    pos + copied + f_copied < inode->v.i_size) {
+			iov_iter_revert(iter, f_copied);
 			folio_zero_range(f, 0, folio_size(f));
 			folios_trunc(&folios, fi);
 			break;
diff --git a/libbcachefs/fs-io-pagecache.c b/libbcachefs/fs-io-pagecache.c
index 2c1ef13d..1e60eead 100644
--- a/libbcachefs/fs-io-pagecache.c
+++ b/libbcachefs/fs-io-pagecache.c
@@ -698,20 +698,26 @@ loff_t bch2_seek_pagecache_data(struct inode *vinode,
 	return end_offset;
 }
 
+/*
+ * Search for a hole in a folio.
+ *
+ * The filemap layer returns -ENOENT if no folio exists, so reuse the same error
+ * code to indicate a pagecache hole exists at the returned offset. Otherwise
+ * return 0 if the folio is filled with data, or an error code. This function
+ * can return -EAGAIN if nonblock is specified.
+ */
 static int folio_hole_offset(struct address_space *mapping, loff_t *offset,
 			      unsigned min_replicas, bool nonblock)
 {
 	struct folio *folio;
 	struct bch_folio *s;
 	unsigned i, sectors;
-	bool ret = true;
+	int ret = -ENOENT;
 
 	folio = __filemap_get_folio(mapping, *offset >> PAGE_SHIFT,
 				    FGP_LOCK|(nonblock ? FGP_NOWAIT : 0), 0);
-	if (folio == ERR_PTR(-EAGAIN))
-		return -EAGAIN;
-	if (IS_ERR_OR_NULL(folio))
-		return true;
+	if (IS_ERR(folio))
+		return PTR_ERR(folio);
 
 	s = bch2_folio(folio);
 	if (!s)
@@ -727,7 +733,7 @@ static int folio_hole_offset(struct address_space *mapping, loff_t *offset,
 		}
 
 	*offset = folio_end_pos(folio);
-	ret = false;
+	ret = 0;
 unlock:
 	folio_unlock(folio);
 	folio_put(folio);
@@ -742,11 +748,13 @@ loff_t bch2_seek_pagecache_hole(struct inode *vinode,
 {
 	struct address_space *mapping = vinode->i_mapping;
 	loff_t offset = start_offset;
+	loff_t ret = 0;
 
-	while (offset < end_offset &&
-	       !folio_hole_offset(mapping, &offset, min_replicas, nonblock))
-		;
+	while (!ret && offset < end_offset)
+		ret = folio_hole_offset(mapping, &offset, min_replicas, nonblock);
 
+	if (ret && ret != -ENOENT)
+		return ret;
 	return min(offset, end_offset);
 }
 
diff --git a/libbcachefs/fs-io.c b/libbcachefs/fs-io.c
index 963c7971..4804e5a4 100644
--- a/libbcachefs/fs-io.c
+++ b/libbcachefs/fs-io.c
@@ -109,7 +109,8 @@ struct inode_new_size {
 	unsigned	fields;
 };
 
-static int inode_set_size(struct bch_inode_info *inode,
+static int inode_set_size(struct btree_trans *trans,
+			  struct bch_inode_info *inode,
 			  struct bch_inode_unpacked *bi,
 			  void *p)
 {
@@ -390,7 +391,8 @@ static int bch2_extend(struct mnt_idmap *idmap,
 	return bch2_setattr_nonsize(idmap, inode, iattr);
 }
 
-static int bch2_truncate_finish_fn(struct bch_inode_info *inode,
+static int bch2_truncate_finish_fn(struct btree_trans *trans,
+				   struct bch_inode_info *inode,
 				   struct bch_inode_unpacked *bi,
 				   void *p)
 {
@@ -398,7 +400,8 @@ static int bch2_truncate_finish_fn(struct bch_inode_info *inode,
 	return 0;
 }
 
-static int bch2_truncate_start_fn(struct bch_inode_info *inode,
+static int bch2_truncate_start_fn(struct btree_trans *trans,
+				  struct bch_inode_info *inode,
 				  struct bch_inode_unpacked *bi, void *p)
 {
 	u64 *new_i_size = p;
@@ -519,7 +522,8 @@ err:
 
 /* fallocate: */
 
-static int inode_update_times_fn(struct bch_inode_info *inode,
+static int inode_update_times_fn(struct btree_trans *trans,
+				 struct bch_inode_info *inode,
 				 struct bch_inode_unpacked *bi, void *p)
 {
 	struct bch_fs *c = inode->v.i_sb->s_fs_info;
diff --git a/libbcachefs/fs-io.h b/libbcachefs/fs-io.h
index c6704618..bb5b709f 100644
--- a/libbcachefs/fs-io.h
+++ b/libbcachefs/fs-io.h
@@ -108,15 +108,15 @@ static inline int bch2_quota_reservation_add(struct bch_fs *c,
 
 #else
 
-static void __bch2_quota_reservation_put(struct bch_fs *c,
+static inline void __bch2_quota_reservation_put(struct bch_fs *c,
 					 struct bch_inode_info *inode,
 					 struct quota_res *res) {}
 
-static void bch2_quota_reservation_put(struct bch_fs *c,
+static inline void bch2_quota_reservation_put(struct bch_fs *c,
 				       struct bch_inode_info *inode,
 				       struct quota_res *res) {}
 
-static int bch2_quota_reservation_add(struct bch_fs *c,
+static inline int bch2_quota_reservation_add(struct bch_fs *c,
 				      struct bch_inode_info *inode,
 				      struct quota_res *res,
 				      unsigned sectors,
diff --git a/libbcachefs/fs-ioctl.c b/libbcachefs/fs-ioctl.c
index dfa1bf73..141bcced 100644
--- a/libbcachefs/fs-ioctl.c
+++ b/libbcachefs/fs-ioctl.c
@@ -31,7 +31,8 @@ struct flags_set {
 	bool			projinherit;
 };
 
-static int bch2_inode_flags_set(struct bch_inode_info *inode,
+static int bch2_inode_flags_set(struct btree_trans *trans,
+				struct bch_inode_info *inode,
 				struct bch_inode_unpacked *bi,
 				void *p)
 {
@@ -124,7 +125,8 @@ static int bch2_ioc_fsgetxattr(struct bch_inode_info *inode,
 	return copy_to_user(arg, &fa, sizeof(fa));
 }
 
-static int fssetxattr_inode_update_fn(struct bch_inode_info *inode,
+static int fssetxattr_inode_update_fn(struct btree_trans *trans,
+				      struct bch_inode_info *inode,
 				      struct bch_inode_unpacked *bi,
 				      void *p)
 {
@@ -135,7 +137,7 @@ static int fssetxattr_inode_update_fn(struct bch_inode_info *inode,
 		bi->bi_project = s->projid;
 	}
 
-	return bch2_inode_flags_set(inode, bi, p);
+	return bch2_inode_flags_set(trans, inode, bi, p);
 }
 
 static int bch2_ioc_fssetxattr(struct bch_fs *c,
@@ -192,7 +194,8 @@ err:
 	return ret;
 }
 
-static int bch2_reinherit_attrs_fn(struct bch_inode_info *inode,
+static int bch2_reinherit_attrs_fn(struct btree_trans *trans,
+				   struct bch_inode_info *inode,
 				   struct bch_inode_unpacked *bi,
 				   void *p)
 {
diff --git a/libbcachefs/fs.c b/libbcachefs/fs.c
index 925f5e52..8958957b 100644
--- a/libbcachefs/fs.c
+++ b/libbcachefs/fs.c
@@ -23,6 +23,7 @@
 #include "journal.h"
 #include "keylist.h"
 #include "quota.h"
+#include "snapshot.h"
 #include "super.h"
 #include "xattr.h"
 
@@ -92,7 +93,7 @@ retry:
 
 	ret   = bch2_inode_peek(&trans, &iter, &inode_u, inode_inum(inode),
 				BTREE_ITER_INTENT) ?:
-		(set ? set(inode, &inode_u, p) : 0) ?:
+		(set ? set(&trans, inode, &inode_u, p) : 0) ?:
 		bch2_inode_write(&trans, &iter, &inode_u) ?:
 		bch2_trans_commit(&trans, NULL, NULL, BTREE_INSERT_NOFAIL);
 
@@ -1237,7 +1238,8 @@ static int bch2_get_name(struct dentry *parent, char *name, struct dentry *child
 	struct bch_inode_unpacked inode_u;
 	subvol_inum target;
 	u32 snapshot;
-	unsigned name_len;
+	struct qstr dirent_name;
+	unsigned name_len = 0;
 	int ret;
 
 	if (!S_ISDIR(dir->v.i_mode))
@@ -1314,9 +1316,10 @@ retry:
 	ret = -ENOENT;
 	goto err;
 found:
-	name_len = min_t(unsigned, bch2_dirent_name_bytes(d), NAME_MAX);
+	dirent_name = bch2_dirent_get_name(d);
 
-	memcpy(name, d.v->d_name, name_len);
+	name_len = min_t(unsigned, dirent_name.len, NAME_MAX);
+	memcpy(name, dirent_name.name, name_len);
 	name[name_len] = '\0';
 err:
 	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
@@ -1414,7 +1417,8 @@ static void bch2_destroy_inode(struct inode *vinode)
 	call_rcu(&vinode->i_rcu, bch2_i_callback);
 }
 
-static int inode_update_times_fn(struct bch_inode_info *inode,
+static int inode_update_times_fn(struct btree_trans *trans,
+				 struct bch_inode_info *inode,
 				 struct bch_inode_unpacked *bi,
 				 void *p)
 {
diff --git a/libbcachefs/fs.h b/libbcachefs/fs.h
index 6170d214..10e11119 100644
--- a/libbcachefs/fs.h
+++ b/libbcachefs/fs.h
@@ -174,7 +174,8 @@ static inline int bch2_set_projid(struct bch_fs *c,
 struct inode *bch2_vfs_inode_get(struct bch_fs *, subvol_inum);
 
 /* returns 0 if we want to do the update, or error is passed up */
-typedef int (*inode_set_fn)(struct bch_inode_info *,
+typedef int (*inode_set_fn)(struct btree_trans *,
+			    struct bch_inode_info *,
 			    struct bch_inode_unpacked *, void *);
 
 void bch2_inode_update_after_write(struct btree_trans *,
diff --git a/libbcachefs/fsck.c b/libbcachefs/fsck.c
index d99c04af..960280b7 100644
--- a/libbcachefs/fsck.c
+++ b/libbcachefs/fsck.c
@@ -12,7 +12,7 @@
 #include "inode.h"
 #include "keylist.h"
 #include "recovery.h"
-#include "subvolume.h"
+#include "snapshot.h"
 #include "super.h"
 #include "xattr.h"
 
@@ -409,6 +409,28 @@ 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)
 {
@@ -1123,7 +1145,8 @@ static int extent_ends_at(struct bch_fs *c,
 
 static int overlapping_extents_found(struct btree_trans *trans,
 				     enum btree_id btree,
-				     struct bpos pos1, struct bkey pos2,
+				     struct bpos pos1, struct snapshots_seen *pos1_seen,
+				     struct bkey pos2,
 				     bool *fixed,
 				     struct extent_end *extent_end)
 {
@@ -1209,10 +1232,24 @@ static int overlapping_extents_found(struct btree_trans *trans,
 
 		*fixed = true;
 
-		if (pos1.snapshot == pos2.p.snapshot)
+		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
+		} 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:
@@ -1254,6 +1291,7 @@ static int check_overlapping_extents(struct btree_trans *trans,
 						SPOS(iter->pos.inode,
 						     i->offset,
 						     i->snapshot),
+						&i->seen,
 						*k.k, fixed, i);
 		if (ret)
 			goto err;
diff --git a/libbcachefs/inode.c b/libbcachefs/inode.c
index e0d41655..8114b6e4 100644
--- a/libbcachefs/inode.c
+++ b/libbcachefs/inode.c
@@ -11,6 +11,7 @@
 #include "extent_update.h"
 #include "inode.h"
 #include "str_hash.h"
+#include "snapshot.h"
 #include "subvolume.h"
 #include "varint.h"
 
@@ -1048,6 +1049,11 @@ static int may_delete_deleted_inode(struct btree_trans *trans, struct bpos pos)
 	if (ret)
 		goto err;
 
+	if (fsck_err_on(S_ISDIR(inode.bi_mode), c,
+			"directory %llu:%u in deleted_inodes btree",
+			pos.offset, pos.snapshot))
+		goto delete;
+
 	if (fsck_err_on(!(inode.bi_flags & BCH_INODE_UNLINKED), c,
 			"non-deleted inode %llu:%u in deleted_inodes btree",
 			pos.offset, pos.snapshot))
diff --git a/libbcachefs/io.c b/libbcachefs/io.c
index f42d9da2..3c614c86 100644
--- a/libbcachefs/io.c
+++ b/libbcachefs/io.c
@@ -380,10 +380,10 @@ int bch2_extent_fallocate(struct btree_trans *trans,
 	struct bch_fs *c = trans->c;
 	struct disk_reservation disk_res = { 0 };
 	struct closure cl;
-	struct open_buckets open_buckets;
+	struct open_buckets open_buckets = { 0 };
 	struct bkey_s_c k;
 	struct bkey_buf old, new;
-	unsigned sectors_allocated;
+	unsigned sectors_allocated = 0;
 	bool have_reservation = false;
 	bool unwritten = opts.nocow &&
 	    c->sb.version >= bcachefs_metadata_version_unwritten_extents;
@@ -392,9 +392,6 @@ int bch2_extent_fallocate(struct btree_trans *trans,
 	bch2_bkey_buf_init(&old);
 	bch2_bkey_buf_init(&new);
 	closure_init_stack(&cl);
-	open_buckets.nr = 0;
-retry:
-	sectors_allocated = 0;
 
 	k = bch2_btree_iter_peek_slot(iter);
 	ret = bkey_err(k);
@@ -413,14 +410,14 @@ retry:
 		 */
 		ret = bch2_disk_reservation_get(c, &disk_res, sectors, new_replicas, 0);
 		if (unlikely(ret))
-			goto out;
+			goto err;
 
 		bch2_bkey_buf_reassemble(&old, c, k);
 	}
 
 	if (have_reservation) {
 		if (!bch2_extents_match(k, bkey_i_to_s_c(old.k)))
-			goto out;
+			goto err;
 
 		bch2_key_resize(&new.k->k, sectors);
 	} else if (!unwritten) {
@@ -452,13 +449,10 @@ retry:
 				opts.data_replicas,
 				opts.data_replicas,
 				BCH_WATERMARK_normal, 0, &cl, &wp);
-		if (ret) {
-			bch2_trans_unlock(trans);
-			closure_sync(&cl);
-			if (bch2_err_matches(ret, BCH_ERR_operation_blocked))
-				goto retry;
-			return ret;
-		}
+		if (bch2_err_matches(ret, BCH_ERR_operation_blocked))
+			ret = -BCH_ERR_transaction_restart_nested;
+		if (ret)
+			goto err;
 
 		sectors = min(sectors, wp->sectors_free);
 		sectors_allocated = sectors;
@@ -477,17 +471,7 @@ retry:
 
 	ret = bch2_extent_update(trans, inum, iter, new.k, &disk_res,
 				 0, i_sectors_delta, true);
-out:
-	if ((atomic_read(&cl.remaining) & CLOSURE_REMAINING_MASK) != 1) {
-		bch2_trans_unlock(trans);
-		closure_sync(&cl);
-	}
-
-	if (bch2_err_matches(ret, BCH_ERR_transaction_restart)) {
-		bch2_trans_begin(trans);
-		goto retry;
-	}
-
+err:
 	if (!ret && sectors_allocated)
 		bch2_increment_clock(c, sectors_allocated, WRITE);
 
@@ -496,6 +480,11 @@ out:
 	bch2_bkey_buf_exit(&new, c);
 	bch2_bkey_buf_exit(&old, c);
 
+	if (closure_nr_remaining(&cl) != 1) {
+		bch2_trans_unlock(trans);
+		closure_sync(&cl);
+	}
+
 	return ret;
 }
 
@@ -710,13 +699,15 @@ static void bch2_write_done(struct closure *cl)
 	struct bch_write_op *op = container_of(cl, struct bch_write_op, cl);
 	struct bch_fs *c = op->c;
 
+	EBUG_ON(op->open_buckets.nr);
+
+	bch2_time_stats_update(&c->times[BCH_TIME_data_write], op->start_time);
 	bch2_disk_reservation_put(c, &op->res);
+
 	if (!(op->flags & BCH_WRITE_MOVE))
 		bch2_write_ref_put(c, BCH_WRITE_REF_write);
 	bch2_keylist_free(&op->insert_keys, op->inline_keys);
 
-	bch2_time_stats_update(&c->times[BCH_TIME_data_write], op->start_time);
-
 	EBUG_ON(cl->parent);
 	closure_debug_destroy(cl);
 	if (op->end_io)
diff --git a/libbcachefs/quota.c b/libbcachefs/quota.c
index 4f0654ff..ca99772a 100644
--- a/libbcachefs/quota.c
+++ b/libbcachefs/quota.c
@@ -5,7 +5,7 @@
 #include "error.h"
 #include "inode.h"
 #include "quota.h"
-#include "subvolume.h"
+#include "snapshot.h"
 #include "super-io.h"
 
 static const char * const bch2_quota_types[] = {
diff --git a/libbcachefs/rebalance.c b/libbcachefs/rebalance.c
index c3d57723..15ce3ecb 100644
--- a/libbcachefs/rebalance.c
+++ b/libbcachefs/rebalance.c
@@ -113,6 +113,10 @@ static void rebalance_work_accumulate(struct rebalance_work *w,
 	unsigned percent_full;
 	u64 work = dev_work + unknown_dev;
 
+	/* avoid divide by 0 */
+	if (!capacity)
+		return;
+
 	if (work < dev_work || work < unknown_dev)
 		work = U64_MAX;
 	work = min(work, capacity);
diff --git a/libbcachefs/recovery.c b/libbcachefs/recovery.c
index 33a68a33..30efb3c9 100644
--- a/libbcachefs/recovery.c
+++ b/libbcachefs/recovery.c
@@ -25,6 +25,7 @@
 #include "recovery.h"
 #include "replicas.h"
 #include "sb-clean.h"
+#include "snapshot.h"
 #include "subvolume.h"
 #include "super-io.h"
 
diff --git a/linux/six.c b/libbcachefs/six.c
index 0b9c4bb7..14cffa68 100644
--- a/linux/six.c
+++ b/libbcachefs/six.c
@@ -8,11 +8,13 @@
 #include <linux/sched.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/rt.h>
-#include <linux/six.h>
+#include <linux/sched/task.h>
 #include <linux/slab.h>
 
 #include <trace/events/lock.h>
 
+#include "six.h"
+
 #ifdef DEBUG
 #define EBUG_ON(cond)			BUG_ON(cond)
 #else
@@ -222,15 +224,23 @@ again:
 		if (ret <= 0)
 			goto unlock;
 
+		/*
+		 * Similar to percpu_rwsem_wake_function(), we need to guard
+		 * against the wakee noticing w->lock_acquired, returning, and
+		 * then exiting before we do the wakeup:
+		 */
+		task = get_task_struct(w->task);
 		__list_del(w->list.prev, w->list.next);
-		task = w->task;
 		/*
-		 * Do no writes to @w besides setting lock_acquired - otherwise
-		 * we would need a memory barrier:
+		 * The release barrier here ensures the ordering of the
+		 * __list_del before setting w->lock_acquired; @w is on the
+		 * stack of the thread doing the waiting and will be reused
+		 * after it sees w->lock_acquired with no other locking:
+		 * pairs with smp_load_acquire() in six_lock_slowpath()
 		 */
-		barrier();
-		w->lock_acquired = true;
+		smp_store_release(&w->lock_acquired, true);
 		wake_up_process(task);
+		put_task_struct(task);
 	}
 
 	six_clear_bitmask(lock, SIX_LOCK_WAITING_read << lock_type);
@@ -501,17 +511,32 @@ static int six_lock_slowpath(struct six_lock *lock, enum six_lock_type type,
 	while (1) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 
-		if (wait->lock_acquired)
+		/*
+		 * Ensures that writes to the waitlist entry happen after we see
+		 * wait->lock_acquired: pairs with the smp_store_release in
+		 * __six_lock_wakeup
+		 */
+		if (smp_load_acquire(&wait->lock_acquired))
 			break;
 
 		ret = should_sleep_fn ? should_sleep_fn(lock, p) : 0;
 		if (unlikely(ret)) {
+			bool acquired;
+
+			/*
+			 * If should_sleep_fn() returns an error, we are
+			 * required to return that error even if we already
+			 * acquired the lock - should_sleep_fn() might have
+			 * modified external state (e.g. when the deadlock cycle
+			 * detector in bcachefs issued a transaction restart)
+			 */
 			raw_spin_lock(&lock->wait_lock);
-			if (!wait->lock_acquired)
+			acquired = wait->lock_acquired;
+			if (!acquired)
 				list_del(&wait->list);
 			raw_spin_unlock(&lock->wait_lock);
 
-			if (unlikely(wait->lock_acquired))
+			if (unlikely(acquired))
 				do_six_unlock_type(lock, type);
 			break;
 		}
diff --git a/include/linux/six.h b/libbcachefs/six.h
index 394da423..394da423 100644
--- a/include/linux/six.h
+++ b/libbcachefs/six.h
diff --git a/libbcachefs/snapshot.c b/libbcachefs/snapshot.c
new file mode 100644
index 00000000..82425917
--- /dev/null
+++ b/libbcachefs/snapshot.c
@@ -0,0 +1,886 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "bcachefs.h"
+#include "btree_key_cache.h"
+#include "btree_update.h"
+#include "errcode.h"
+#include "error.h"
+#include "fs.h"
+#include "snapshot.h"
+
+#include <linux/random.h>
+
+/*
+ * Snapshot trees:
+ *
+ * Keys in BTREE_ID_snapshot_trees identify a whole tree of snapshot nodes; they
+ * exist to provide a stable identifier for the whole lifetime of a 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;
+}
+
+struct bkey_i_snapshot_tree *
+__bch2_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 bch2_snapshot_tree_create(struct btree_trans *trans,
+				u32 root_id, u32 subvol_id, u32 *tree_id)
+{
+	struct bkey_i_snapshot_tree *n_tree =
+		__bch2_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: */
+
+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 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)
+		kvfree_rcu(old);
+
+	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);
+}
+
+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;
+}
+
+int bch2_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);
+}
+
+int bch2_snapshot_live(struct btree_trans *trans, u32 id)
+{
+	struct bch_snapshot v;
+	int ret;
+
+	if (!id)
+		return 0;
+
+	ret = bch2_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);
+}
+
+/*
+ * If @k is a snapshot with just one live child, it's part of a linear chain,
+ * which we consider to be an equivalence class: and then after snapshot
+ * deletion cleanup, there should only be a single key at a given position in
+ * this equivalence class.
+ *
+ * This sets the equivalence class of @k to be the child's equivalence class, if
+ * it's part of such a linear chain: this correctly sets equivalence classes on
+ * startup if we run leaf to root (i.e. in natural key order).
+ */
+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 = bch2_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 = bch2_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));
+}
+
+u32 bch2_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 = bch2_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) ?:
+			bch2_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 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 = bch2_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 = bch2_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(bch2_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;
+}
+
+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;
+}
+
+void bch2_fs_snapshots_exit(struct bch_fs *c)
+{
+	kfree(rcu_dereference_protected(c->snapshots, true));
+}
diff --git a/libbcachefs/snapshot.h b/libbcachefs/snapshot.h
new file mode 100644
index 00000000..c59b7e9e
--- /dev/null
+++ b/libbcachefs/snapshot.h
@@ -0,0 +1,250 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_SNAPSHOT_H
+#define _BCACHEFS_SNAPSHOT_H
+
+enum bkey_invalid_flags;
+
+void bch2_snapshot_tree_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
+int bch2_snapshot_tree_invalid(const struct bch_fs *, struct bkey_s_c,
+			       enum bkey_invalid_flags, struct printbuf *);
+
+#define bch2_bkey_ops_snapshot_tree ((struct bkey_ops) {	\
+	.key_invalid	= bch2_snapshot_tree_invalid,		\
+	.val_to_text	= bch2_snapshot_tree_to_text,		\
+	.min_val_size	= 8,					\
+})
+
+struct bkey_i_snapshot_tree *__bch2_snapshot_tree_create(struct btree_trans *);
+
+int bch2_snapshot_tree_lookup(struct btree_trans *, u32, struct bch_snapshot_tree *);
+
+void bch2_snapshot_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
+int bch2_snapshot_invalid(const struct bch_fs *, struct bkey_s_c,
+			  enum bkey_invalid_flags, struct printbuf *);
+int bch2_mark_snapshot(struct btree_trans *, enum btree_id, unsigned,
+		       struct bkey_s_c, struct bkey_s_c, unsigned);
+
+#define bch2_bkey_ops_snapshot ((struct bkey_ops) {		\
+	.key_invalid	= bch2_snapshot_invalid,		\
+	.val_to_text	= bch2_snapshot_to_text,		\
+	.atomic_trigger	= bch2_mark_snapshot,			\
+	.min_val_size	= 24,					\
+})
+
+static inline struct snapshot_t *__snapshot_t(struct snapshot_table *t, u32 id)
+{
+	return &t->s[U32_MAX - id];
+}
+
+static inline const struct snapshot_t *snapshot_t(struct bch_fs *c, u32 id)
+{
+	return __snapshot_t(rcu_dereference(c->snapshots), id);
+}
+
+static inline u32 bch2_snapshot_tree(struct bch_fs *c, u32 id)
+{
+	rcu_read_lock();
+	id = snapshot_t(c, id)->tree;
+	rcu_read_unlock();
+
+	return id;
+}
+
+static inline u32 __bch2_snapshot_parent_early(struct bch_fs *c, u32 id)
+{
+	return snapshot_t(c, id)->parent;
+}
+
+static inline u32 bch2_snapshot_parent_early(struct bch_fs *c, u32 id)
+{
+	rcu_read_lock();
+	id = __bch2_snapshot_parent_early(c, id);
+	rcu_read_unlock();
+
+	return id;
+}
+
+static inline u32 __bch2_snapshot_parent(struct bch_fs *c, u32 id)
+{
+#ifdef CONFIG_BCACHEFS_DEBUG
+	u32 parent = snapshot_t(c, id)->parent;
+
+	if (parent &&
+	    snapshot_t(c, id)->depth != snapshot_t(c, parent)->depth + 1)
+		panic("id %u depth=%u parent %u depth=%u\n",
+		      id, snapshot_t(c, id)->depth,
+		      parent, snapshot_t(c, parent)->depth);
+
+	return parent;
+#else
+	return snapshot_t(c, id)->parent;
+#endif
+}
+
+static inline u32 bch2_snapshot_parent(struct bch_fs *c, u32 id)
+{
+	rcu_read_lock();
+	id = __bch2_snapshot_parent(c, id);
+	rcu_read_unlock();
+
+	return id;
+}
+
+static inline u32 bch2_snapshot_nth_parent(struct bch_fs *c, u32 id, u32 n)
+{
+	rcu_read_lock();
+	while (n--)
+		id = __bch2_snapshot_parent(c, id);
+	rcu_read_unlock();
+
+	return id;
+}
+
+u32 bch2_snapshot_skiplist_get(struct bch_fs *, u32);
+
+static inline u32 bch2_snapshot_root(struct bch_fs *c, u32 id)
+{
+	u32 parent;
+
+	rcu_read_lock();
+	while ((parent = __bch2_snapshot_parent(c, id)))
+		id = parent;
+	rcu_read_unlock();
+
+	return id;
+}
+
+static inline u32 __bch2_snapshot_equiv(struct bch_fs *c, u32 id)
+{
+	return snapshot_t(c, id)->equiv;
+}
+
+static inline u32 bch2_snapshot_equiv(struct bch_fs *c, u32 id)
+{
+	rcu_read_lock();
+	id = __bch2_snapshot_equiv(c, id);
+	rcu_read_unlock();
+
+	return id;
+}
+
+static inline bool bch2_snapshot_is_equiv(struct bch_fs *c, u32 id)
+{
+	return id == bch2_snapshot_equiv(c, id);
+}
+
+static inline bool bch2_snapshot_is_internal_node(struct bch_fs *c, u32 id)
+{
+	const struct snapshot_t *s;
+	bool ret;
+
+	rcu_read_lock();
+	s = snapshot_t(c, id);
+	ret = s->children[0];
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static inline u32 bch2_snapshot_is_leaf(struct bch_fs *c, u32 id)
+{
+	return !bch2_snapshot_is_internal_node(c, id);
+}
+
+static inline u32 bch2_snapshot_sibling(struct bch_fs *c, u32 id)
+{
+	const struct snapshot_t *s;
+	u32 parent = __bch2_snapshot_parent(c, id);
+
+	if (!parent)
+		return 0;
+
+	s = snapshot_t(c, __bch2_snapshot_parent(c, id));
+	if (id == s->children[0])
+		return s->children[1];
+	if (id == s->children[1])
+		return s->children[0];
+	return 0;
+}
+
+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;
+}
+
+bool __bch2_snapshot_is_ancestor(struct bch_fs *, u32, u32);
+
+static inline bool bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
+{
+	return id == ancestor
+		? true
+		: __bch2_snapshot_is_ancestor(c, id, ancestor);
+}
+
+static inline bool bch2_snapshot_has_children(struct bch_fs *c, u32 id)
+{
+	const struct snapshot_t *t;
+	bool ret;
+
+	rcu_read_lock();
+	t = snapshot_t(c, id);
+	ret = (t->children[0]|t->children[1]) != 0;
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static inline bool snapshot_list_has_id(snapshot_id_list *s, u32 id)
+{
+	u32 *i;
+
+	darray_for_each(*s, i)
+		if (*i == id)
+			return true;
+	return false;
+}
+
+static inline bool snapshot_list_has_ancestor(struct bch_fs *c, snapshot_id_list *s, u32 id)
+{
+	u32 *i;
+
+	darray_for_each(*s, i)
+		if (bch2_snapshot_is_ancestor(c, id, *i))
+			return true;
+	return false;
+}
+
+static inline int snapshot_list_add(struct bch_fs *c, snapshot_id_list *s, u32 id)
+{
+	int ret;
+
+	BUG_ON(snapshot_list_has_id(s, id));
+	ret = darray_push(s, id);
+	if (ret)
+		bch_err(c, "error reallocating snapshot_id_list (size %zu)", s->size);
+	return ret;
+}
+
+int bch2_snapshot_lookup(struct btree_trans *trans, u32 id,
+			 struct bch_snapshot *s);
+int bch2_snapshot_get_subvol(struct btree_trans *, u32,
+			     struct bch_subvolume *);
+int bch2_snapshot_live(struct btree_trans *trans, u32 id);
+int bch2_snapshot_set_equiv(struct btree_trans *trans, struct bkey_s_c k);
+
+/* only exported for tests: */
+int bch2_snapshot_node_create(struct btree_trans *, u32,
+			      u32 *, u32 *, unsigned);
+
+int bch2_check_snapshot_trees(struct bch_fs *);
+int bch2_check_snapshots(struct bch_fs *);
+int bch2_snapshots_read(struct bch_fs *);
+void bch2_fs_snapshots_exit(struct bch_fs *);
+
+#endif /* _BCACHEFS_SNAPSHOT_H */
diff --git a/libbcachefs/subvolume.c b/libbcachefs/subvolume.c
index 736afb62..571cb280 100644
--- a/libbcachefs/subvolume.c
+++ b/libbcachefs/subvolume.c
@@ -6,866 +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;
-}
-
-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)
-		kvfree_rcu(old);
-
-	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)
@@ -881,7 +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",
@@ -949,27 +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:
  */
@@ -1126,7 +252,7 @@ static int create_snapids(struct btree_trans *trans, u32 parent, u32 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));
+			n->v.skip[j] = cpu_to_le32(bch2_snapshot_skiplist_get(c, parent));
 
 		bubble_sort(n->v.skip, ARRAY_SIZE(n->v.skip), cmp_le32);
 		SET_BCH_SNAPSHOT_SUBVOL(&n->v, true);
@@ -1196,7 +322,7 @@ static int bch2_snapshot_node_create_tree(struct btree_trans *trans,
 	struct bkey_i_snapshot_tree *n_tree;
 	int ret;
 
-	n_tree = __snapshot_tree_create(trans);
+	n_tree = __bch2_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);
@@ -1224,6 +350,18 @@ int bch2_snapshot_node_create(struct btree_trans *trans, u32 parent,
 
 }
 
+/*
+ * If we have an unlinked inode in an internal snapshot node, and the inode
+ * really has been deleted in all child snapshots, how does this get cleaned up?
+ *
+ * first there is the problem of how keys that have been overwritten in all
+ * child snapshots get deleted (unimplemented?), but inodes may perhaps be
+ * special?
+ *
+ * also: unlinked inode in internal snapshot appears to not be getting deleted
+ * correctly if inode doesn't exist in leaf snapshots
+ */
+
 static int snapshot_delete_key(struct btree_trans *trans,
 			       struct btree_iter *iter,
 			       struct bkey_s_c k,
@@ -1247,6 +385,11 @@ static int snapshot_delete_key(struct btree_trans *trans,
 	}
 }
 
+/*
+ * For a given snapshot, if it doesn't have a subvolume that points to it, and
+ * it doesn't have child snapshot nodes - it's now redundant and we can mark it
+ * as deleted.
+ */
 static int bch2_delete_redundant_snapshot(struct btree_trans *trans, struct btree_iter *iter,
 					  struct bkey_s_c k)
 {
@@ -1265,8 +408,8 @@ static int bch2_delete_redundant_snapshot(struct btree_trans *trans, struct btre
 	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]);
+	ret   = bch2_snapshot_live(trans, children[0]) ?:
+		bch2_snapshot_live(trans, children[1]);
 	if (ret < 0)
 		return ret;
 
@@ -1459,26 +602,27 @@ 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;
 }
@@ -1508,7 +652,12 @@ 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)
 {
diff --git a/libbcachefs/subvolume.h b/libbcachefs/subvolume.h
index 6905e91a..8d4c50f4 100644
--- a/libbcachefs/subvolume.h
+++ b/libbcachefs/subvolume.h
@@ -7,225 +7,8 @@
 
 enum bkey_invalid_flags;
 
-void bch2_snapshot_tree_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
-int bch2_snapshot_tree_invalid(const struct bch_fs *, struct bkey_s_c,
-			       enum bkey_invalid_flags, struct printbuf *);
-
-#define bch2_bkey_ops_snapshot_tree ((struct bkey_ops) {	\
-	.key_invalid	= bch2_snapshot_tree_invalid,		\
-	.val_to_text	= bch2_snapshot_tree_to_text,		\
-	.min_val_size	= 8,					\
-})
-
-int bch2_snapshot_tree_lookup(struct btree_trans *, u32, struct bch_snapshot_tree *);
-
-void bch2_snapshot_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
-int bch2_snapshot_invalid(const struct bch_fs *, struct bkey_s_c,
-			  enum bkey_invalid_flags, struct printbuf *);
-int bch2_mark_snapshot(struct btree_trans *, enum btree_id, unsigned,
-		       struct bkey_s_c, struct bkey_s_c, unsigned);
-
-#define bch2_bkey_ops_snapshot ((struct bkey_ops) {		\
-	.key_invalid	= bch2_snapshot_invalid,		\
-	.val_to_text	= bch2_snapshot_to_text,		\
-	.atomic_trigger	= bch2_mark_snapshot,			\
-	.min_val_size	= 24,					\
-})
-
-static inline struct snapshot_t *__snapshot_t(struct snapshot_table *t, u32 id)
-{
-	return &t->s[U32_MAX - id];
-}
-
-static inline const struct snapshot_t *snapshot_t(struct bch_fs *c, u32 id)
-{
-	return __snapshot_t(rcu_dereference(c->snapshots), id);
-}
-
-static inline u32 bch2_snapshot_tree(struct bch_fs *c, u32 id)
-{
-	rcu_read_lock();
-	id = snapshot_t(c, id)->tree;
-	rcu_read_unlock();
-
-	return id;
-}
-
-static inline u32 __bch2_snapshot_parent_early(struct bch_fs *c, u32 id)
-{
-	return snapshot_t(c, id)->parent;
-}
-
-static inline u32 bch2_snapshot_parent_early(struct bch_fs *c, u32 id)
-{
-	rcu_read_lock();
-	id = __bch2_snapshot_parent_early(c, id);
-	rcu_read_unlock();
-
-	return id;
-}
-
-static inline u32 __bch2_snapshot_parent(struct bch_fs *c, u32 id)
-{
-#ifdef CONFIG_BCACHEFS_DEBUG
-	u32 parent = snapshot_t(c, id)->parent;
-
-	if (parent &&
-	    snapshot_t(c, id)->depth != snapshot_t(c, parent)->depth + 1)
-		panic("id %u depth=%u parent %u depth=%u\n",
-		      id, snapshot_t(c, id)->depth,
-		      parent, snapshot_t(c, parent)->depth);
-
-	return parent;
-#else
-	return snapshot_t(c, id)->parent;
-#endif
-}
-
-static inline u32 bch2_snapshot_parent(struct bch_fs *c, u32 id)
-{
-	rcu_read_lock();
-	id = __bch2_snapshot_parent(c, id);
-	rcu_read_unlock();
-
-	return id;
-}
-
-static inline u32 bch2_snapshot_nth_parent(struct bch_fs *c, u32 id, u32 n)
-{
-	rcu_read_lock();
-	while (n--)
-		id = __bch2_snapshot_parent(c, id);
-	rcu_read_unlock();
-
-	return id;
-}
-
-static inline u32 bch2_snapshot_root(struct bch_fs *c, u32 id)
-{
-	u32 parent;
-
-	rcu_read_lock();
-	while ((parent = __bch2_snapshot_parent(c, id)))
-		id = parent;
-	rcu_read_unlock();
-
-	return id;
-}
-
-static inline u32 __bch2_snapshot_equiv(struct bch_fs *c, u32 id)
-{
-	return snapshot_t(c, id)->equiv;
-}
-
-static inline u32 bch2_snapshot_equiv(struct bch_fs *c, u32 id)
-{
-	rcu_read_lock();
-	id = __bch2_snapshot_equiv(c, id);
-	rcu_read_unlock();
-
-	return id;
-}
-
-static inline bool bch2_snapshot_is_equiv(struct bch_fs *c, u32 id)
-{
-	return id == bch2_snapshot_equiv(c, id);
-}
-
-static inline bool bch2_snapshot_is_internal_node(struct bch_fs *c, u32 id)
-{
-	const struct snapshot_t *s;
-	bool ret;
-
-	rcu_read_lock();
-	s = snapshot_t(c, id);
-	ret = s->children[0];
-	rcu_read_unlock();
-
-	return ret;
-}
-
-static inline u32 bch2_snapshot_is_leaf(struct bch_fs *c, u32 id)
-{
-	return !bch2_snapshot_is_internal_node(c, id);
-}
-
-static inline u32 bch2_snapshot_sibling(struct bch_fs *c, u32 id)
-{
-	const struct snapshot_t *s;
-	u32 parent = __bch2_snapshot_parent(c, id);
-
-	if (!parent)
-		return 0;
-
-	s = snapshot_t(c, __bch2_snapshot_parent(c, id));
-	if (id == s->children[0])
-		return s->children[1];
-	if (id == s->children[1])
-		return s->children[0];
-	return 0;
-}
-
-bool __bch2_snapshot_is_ancestor(struct bch_fs *, u32, u32);
-
-static inline bool bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
-{
-	return id == ancestor
-		? true
-		: __bch2_snapshot_is_ancestor(c, id, ancestor);
-}
-
-static inline bool bch2_snapshot_has_children(struct bch_fs *c, u32 id)
-{
-	const struct snapshot_t *t;
-	bool ret;
-
-	rcu_read_lock();
-	t = snapshot_t(c, id);
-	ret = (t->children[0]|t->children[1]) != 0;
-	rcu_read_unlock();
-
-	return ret;
-}
-
-static inline bool snapshot_list_has_id(snapshot_id_list *s, u32 id)
-{
-	u32 *i;
-
-	darray_for_each(*s, i)
-		if (*i == id)
-			return true;
-	return false;
-}
-
-static inline bool snapshot_list_has_ancestor(struct bch_fs *c, snapshot_id_list *s, u32 id)
-{
-	u32 *i;
-
-	darray_for_each(*s, i)
-		if (bch2_snapshot_is_ancestor(c, id, *i))
-			return true;
-	return false;
-}
-
-static inline int snapshot_list_add(struct bch_fs *c, snapshot_id_list *s, u32 id)
-{
-	int ret;
-
-	BUG_ON(snapshot_list_has_id(s, id));
-	ret = darray_push(s, id);
-	if (ret)
-		bch_err(c, "error reallocating snapshot_id_list (size %zu)", s->size);
-	return ret;
-}
-
-int bch2_check_snapshot_trees(struct bch_fs *);
-int bch2_check_snapshots(struct bch_fs *);
 int bch2_check_subvols(struct bch_fs *);
 
-void bch2_fs_snapshots_exit(struct bch_fs *);
-int bch2_snapshots_read(struct bch_fs *);
-
 int bch2_subvolume_invalid(const struct bch_fs *, struct bkey_s_c,
 			   unsigned, struct printbuf *);
 void bch2_subvolume_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
@@ -238,14 +21,8 @@ void bch2_subvolume_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c)
 
 int bch2_subvolume_get(struct btree_trans *, unsigned,
 		       bool, int, struct bch_subvolume *);
-int bch2_snapshot_get_subvol(struct btree_trans *, u32,
-			     struct bch_subvolume *);
 int bch2_subvolume_get_snapshot(struct btree_trans *, u32, u32 *);
 
-/* only exported for tests: */
-int bch2_snapshot_node_create(struct btree_trans *, u32,
-			      u32 *, u32 *, unsigned);
-
 int bch2_delete_dead_snapshots(struct bch_fs *);
 void bch2_delete_dead_snapshots_async(struct bch_fs *);
 
diff --git a/libbcachefs/super.c b/libbcachefs/super.c
index 5c62fcf3..48670c8b 100644
--- a/libbcachefs/super.c
+++ b/libbcachefs/super.c
@@ -48,6 +48,7 @@
 #include "recovery.h"
 #include "replicas.h"
 #include "sb-clean.h"
+#include "snapshot.h"
 #include "subvolume.h"
 #include "super.h"
 #include "super-io.h"
diff --git a/libbcachefs/tests.c b/libbcachefs/tests.c
index 1d4b0a58..72389c73 100644
--- a/libbcachefs/tests.c
+++ b/libbcachefs/tests.c
@@ -4,7 +4,7 @@
 #include "bcachefs.h"
 #include "btree_update.h"
 #include "journal_reclaim.h"
-#include "subvolume.h"
+#include "snapshot.h"
 #include "tests.h"
 
 #include "linux/kthread.h"
diff --git a/libbcachefs/trace.c b/libbcachefs/trace.c
index d294b3d7..33efa600 100644
--- a/libbcachefs/trace.c
+++ b/libbcachefs/trace.c
@@ -8,9 +8,9 @@
 #include "btree_update_interior.h"
 #include "keylist.h"
 #include "opts.h"
+#include "six.h"
 
 #include <linux/blktrace_api.h>
-#include <linux/six.h>
 
 #define CREATE_TRACE_POINTS
 #include "trace.h"
diff --git a/libbcachefs/util.c b/libbcachefs/util.c
index fc834db4..80a6c566 100644
--- a/libbcachefs/util.c
+++ b/libbcachefs/util.c
@@ -269,6 +269,7 @@ void bch2_print_string_as_lines(const char *prefix, const char *lines)
 
 int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *task)
 {
+#ifdef CONFIG_STACKTRACE
 	unsigned nr_entries = 0;
 	int ret = 0;
 
@@ -289,6 +290,9 @@ int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *task)
 	up_read(&task->signal->exec_update_lock);
 
 	return ret;
+#else
+	return 0;
+#endif
 }
 
 void bch2_prt_backtrace(struct printbuf *out, bch_stacktrace *stack)
diff --git a/libbcachefs/util.h b/libbcachefs/util.h
index 5b98ece3..d06671a0 100644
--- a/libbcachefs/util.h
+++ b/libbcachefs/util.h
@@ -845,6 +845,11 @@ static inline int u8_cmp(u8 l, u8 r)
 	return cmp_int(l, r);
 }
 
+static inline int cmp_le32(__le32 l, __le32 r)
+{
+	return cmp_int(le32_to_cpu(l), le32_to_cpu(r));
+}
+
 #include <linux/uuid.h>
 
 #endif /* _BCACHEFS_UTIL_H */
diff --git a/libbcachefs/xattr.c b/libbcachefs/xattr.c
index 70f78006..6f6b3caf 100644
--- a/libbcachefs/xattr.c
+++ b/libbcachefs/xattr.c
@@ -494,7 +494,8 @@ struct inode_opt_set {
 	bool			defined;
 };
 
-static int inode_opt_set_fn(struct bch_inode_info *inode,
+static int inode_opt_set_fn(struct btree_trans *trans,
+			    struct bch_inode_info *inode,
 			    struct bch_inode_unpacked *bi,
 			    void *p)
 {
diff --git a/linux/closure.c b/linux/closure.c
index 0855e698..2958169c 100644
--- a/linux/closure.c
+++ b/linux/closure.c
@@ -17,8 +17,9 @@ static inline void closure_put_after_sub(struct closure *cl, int flags)
 {
 	int r = flags & CLOSURE_REMAINING_MASK;
 
-	BUG_ON(flags & CLOSURE_GUARD_MASK);
-	BUG_ON(!r && (flags & ~CLOSURE_DESTRUCTOR));
+	if ((flags & CLOSURE_GUARD_MASK) ||
+	    (!r && (flags & ~CLOSURE_DESTRUCTOR)))
+		panic("closure_put_after_sub: bogus flags %x remaining %i", flags, r);
 
 	if (!r) {
 		if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) {