bcachefs: Split up btree_update_leaf.c

We now have
  btree_trans_commit.c
  btree_update.c
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/Makefile

@@ -15,8 +15,9 @@ bcachefs-y		:=	\
 	btree_iter.o		\
 	btree_key_cache.o	\
 	btree_locking.o		\
+	btree_trans_commit.o	\
+	btree_update.o		\
 	btree_update_interior.o	\
-	btree_update_leaf.o	\
 	btree_write_buffer.o	\
 	buckets.o		\
 	buckets_waiting_for_journal.o	\

fs/bcachefs/btree_gc.h

@@ -2,6 +2,7 @@
 #ifndef _BCACHEFS_BTREE_GC_H
 #define _BCACHEFS_BTREE_GC_H
 
+#include "bkey.h"
 #include "btree_types.h"
 
 int bch2_check_topology(struct bch_fs *);

fs/bcachefs/btree_iter.h

@@ -221,6 +221,22 @@ struct btree_path *bch2_path_get(struct btree_trans *, enum btree_id, struct bpo
 				 unsigned, unsigned, unsigned, unsigned long);
 struct bkey_s_c bch2_btree_path_peek_slot(struct btree_path *, struct bkey *);
 
+/*
+ * bch2_btree_path_peek_slot() for a cached iterator might return a key in a
+ * different snapshot:
+ */
+static inline struct bkey_s_c bch2_btree_path_peek_slot_exact(struct btree_path *path, struct bkey *u)
+{
+	struct bkey_s_c k = bch2_btree_path_peek_slot(path, u);
+
+	if (k.k && bpos_eq(path->pos, k.k->p))
+		return k;
+
+	bkey_init(u);
+	u->p = path->pos;
+	return (struct bkey_s_c) { u, NULL };
+}
+
 struct bkey_i *bch2_btree_journal_peek_slot(struct btree_trans *,
 					struct btree_iter *, struct bpos);