bcachefs: Move extent overwrite handling out of core btree code

Ever since the btree code was first written, handling of overwriting
existing extents - including partially overwriting and splittin existing
extents - was handled as part of the core btree insert path. The modern
transaction and iterator infrastructure didn't exist then, so that was
the only way for it to be done.

This patch moves that outside of the core btree code to a pass that runs
at transaction commit time.

This is a significant simplification to the btree code and overall
reduction in code size, but more importantly it gets us much closer to
the core btree code being completely independent of extents and is
important prep work for snapshots.

This introduces a new feature bit; the old and new extent update models
are incompatible when the filesystem needs journal replay.

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

1 files changed, 14 insertions, 9 deletions

diff --git a/fs/bcachefs/btree_update_interior.h b/fs/bcachefs/btree_update_interior.h
index e3204f32cc68..f6aceed89427 100644
--- a/fs/bcachefs/btree_update_interior.h
+++ b/fs/bcachefs/btree_update_interior.h
@@ -303,18 +303,23 @@ static inline struct btree_node_entry *want_new_bset(struct bch_fs *c,
 }
 
 static inline void push_whiteout(struct bch_fs *c, struct btree *b,
-				 struct bkey_packed *k)
+				 struct bpos pos)
 {
-	unsigned u64s = bkeyp_key_u64s(&b->format, k);
-	struct bkey_packed *dst;
+	struct bkey_packed k;
 
-	BUG_ON(u64s > bch_btree_keys_u64s_remaining(c, b));
+	BUG_ON(bch_btree_keys_u64s_remaining(c, b) < BKEY_U64s);
 
-	b->whiteout_u64s += bkeyp_key_u64s(&b->format, k);
-	dst = unwritten_whiteouts_start(c, b);
-	memcpy_u64s(dst, k, u64s);
-	dst->u64s = u64s;
-	dst->type = KEY_TYPE_deleted;
+	if (!bkey_pack_pos(&k, pos, b)) {
+		struct bkey *u = (void *) &k;
+
+		bkey_init(u);
+		u->p = pos;
+	}
+
+	k.needs_whiteout = true;
+
+	b->whiteout_u64s += k.u64s;
+	bkey_copy(unwritten_whiteouts_start(c, b), &k);
 }
 
 /*