reftable/stack: return stack segments directly

The `stack_table_sizes_for_compaction()` function returns individual
sizes of each reftable table. This function is only called by
`reftable_stack_auto_compact()` to decide which tables need to be
compacted, if any.

Modify the function to directly return the segments, which avoids the
extra step of receiving the sizes only to pass it to
`suggest_compaction_segment()`.

A future commit will also add functionality for checking whether
auto-compaction is necessary without performing it. This change allows
code re-usability in that context.

Signed-off-by: Karthik Nayak <[email protected]>
Acked-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: KarthikNayak

reftable/stack.c

@@ -1626,37 +1626,38 @@ struct segment suggest_compaction_segment(uint64_t *sizes, size_t n,
 	return seg;
 }
 
-static uint64_t *stack_table_sizes_for_compaction(struct reftable_stack *st)
+static int stack_segments_for_compaction(struct reftable_stack *st,
+					 struct segment *seg)
 {
 	int version = (st->opts.hash_id == REFTABLE_HASH_SHA1) ? 1 : 2;
 	int overhead = header_size(version) - 1;
 	uint64_t *sizes;
 
 	REFTABLE_CALLOC_ARRAY(sizes, st->merged->tables_len);
 	if (!sizes)
-		return NULL;
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
 
 	for (size_t i = 0; i < st->merged->tables_len; i++)
 		sizes[i] = st->tables[i]->size - overhead;
 
-	return sizes;
+	*seg = suggest_compaction_segment(sizes, st->merged->tables_len,
+					  st->opts.auto_compaction_factor);
+	reftable_free(sizes);
+
+	return 0;
 }
 
 int reftable_stack_auto_compact(struct reftable_stack *st)
 {
 	struct segment seg;
-	uint64_t *sizes;
+	int err;
 
 	if (st->merged->tables_len < 2)
 		return 0;
 
-	sizes = stack_table_sizes_for_compaction(st);
-	if (!sizes)
-		return REFTABLE_OUT_OF_MEMORY_ERROR;
-
-	seg = suggest_compaction_segment(sizes, st->merged->tables_len,
-					 st->opts.auto_compaction_factor);
-	reftable_free(sizes);
+	err = stack_segments_for_compaction(st, &seg);
+	if (err)
+		return err;
 
 	if (segment_size(&seg) > 0)
 		return stack_compact_range(st, seg.start, seg.end - 1,