bcachefs: Improve reflink repair code

When a reflink pointer points to a missing indirect extent, we replace
it with an error key. Instead of replacing the entire reflink pointer
with an error key, this patch replaces only the missing range with an
error key.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/buckets.c

@@ -1166,18 +1166,22 @@ static int bch2_mark_reservation(struct btree_trans *trans,
 
 static s64 __bch2_mark_reflink_p(struct btree_trans *trans,
 				 struct bkey_s_c_reflink_p p,
+				 u64 start, u64 end,
 				 u64 *idx, unsigned flags, size_t r_idx)
 {
 	struct bch_fs *c = trans->c;
 	struct reflink_gc *r;
 	int add = !(flags & BTREE_TRIGGER_OVERWRITE) ? 1 : -1;
+	u64 next_idx = end;
 	s64 ret = 0;
+	char buf[200];
 
 	if (r_idx >= c->reflink_gc_nr)
 		goto not_found;
 
 	r = genradix_ptr(&c->reflink_gc_table, r_idx);
-	if (*idx < r->offset - r->size)
+	next_idx = min(next_idx, r->offset - r->size);
+	if (*idx < next_idx)
 		goto not_found;
 
 	BUG_ON((s64) r->refcount + add < 0);
@@ -1186,23 +1190,22 @@ static s64 __bch2_mark_reflink_p(struct btree_trans *trans,
 	*idx = r->offset;
 	return 0;
 not_found:
-	*idx = U64_MAX;
-	ret = -EIO;
-
-	/*
-	 * XXX: we're replacing the entire reflink pointer with an error
-	 * key, we should just be replacing the part that was missing:
-	 */
-	if (fsck_err(c, "%llu:%llu len %u points to nonexistent indirect extent %llu",
-		     p.k->p.inode, p.k->p.offset, p.k->size, *idx)) {
+	if (fsck_err(c, "pointer to missing indirect extent\n"
+		     "  %s\n"
+		     "  missing range %llu-%llu",
+		     (bch2_bkey_val_to_text(&PBUF(buf), c, p.s_c), buf),
+		     *idx, next_idx)) {
 		struct bkey_i_error new;
 
 		bkey_init(&new.k);
 		new.k.type	= KEY_TYPE_error;
-		new.k.p		= p.k->p;
-		new.k.size	= p.k->size;
+		new.k.p		= bkey_start_pos(p.k);
+		new.k.p.offset += *idx - start;
+		bch2_key_resize(&new.k, next_idx - *idx);
 		ret = __bch2_btree_insert(trans, BTREE_ID_extents, &new.k_i);
 	}
+
+	*idx = next_idx;
 fsck_err:
 	return ret;
 }
@@ -1216,7 +1219,7 @@ static int bch2_mark_reflink_p(struct btree_trans *trans,
 	struct bkey_s_c_reflink_p p = bkey_s_c_to_reflink_p(k);
 	struct reflink_gc *ref;
 	size_t l, r, m;
-	u64 idx = le64_to_cpu(p.v->idx);
+	u64 idx = le64_to_cpu(p.v->idx), start = idx;
 	u64 end = le64_to_cpu(p.v->idx) + p.k->size;
 	int ret = 0;
 
@@ -1240,7 +1243,8 @@ static int bch2_mark_reflink_p(struct btree_trans *trans,
 	}
 
 	while (idx < end && !ret)
-		ret = __bch2_mark_reflink_p(trans, p, &idx, flags, l++);
+		ret = __bch2_mark_reflink_p(trans, p, start, end,
+					    &idx, flags, l++);
 
 	return ret;
 }