commit-graph.h: use odb in 'load_commit_graph_one_fd_st'

Apply a similar treatment as in the previous patch to pass a 'struct
object_directory *' through the 'load_commit_graph_one_fd_st'
initializer, too.

This prevents a potential bug where a pointer comparison is made to a
NULL 'g->odb', which would cause the commit-graph machinery to think
that a pair of commit-graphs belonged to different alternates when in
fact they do not (i.e., in the case of no '--object-dir').

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit-graph.c

@@ -96,7 +96,7 @@ static int graph_verify(int argc, const char **argv)
 	FREE_AND_NULL(graph_name);
 
 	if (open_ok)
-		graph = load_commit_graph_one_fd_st(fd, &st);
+		graph = load_commit_graph_one_fd_st(fd, &st, odb);
 	else
 		graph = read_commit_graph_one(the_repository, odb);
 

commit-graph.c

@@ -108,7 +108,8 @@ int open_commit_graph(const char *graph_file, int *fd, struct stat *st)
 	return 1;
 }
 
-struct commit_graph *load_commit_graph_one_fd_st(int fd, struct stat *st)
+struct commit_graph *load_commit_graph_one_fd_st(int fd, struct stat *st,
+						 struct object_directory *odb)
 {
 	void *graph_map;
 	size_t graph_size;
@@ -124,7 +125,9 @@ struct commit_graph *load_commit_graph_one_fd_st(int fd, struct stat *st)
 	graph_map = xmmap(NULL, graph_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	ret = parse_commit_graph(graph_map, fd, graph_size);
 
-	if (!ret) {
+	if (ret)
+		ret->odb = odb;
+	else {
 		munmap(graph_map, graph_size);
 		close(fd);
 	}
@@ -299,7 +302,8 @@ struct commit_graph *parse_commit_graph(void *graph_map, int fd,
 	return graph;
 }
 
-static struct commit_graph *load_commit_graph_one(const char *graph_file)
+static struct commit_graph *load_commit_graph_one(const char *graph_file,
+						  struct object_directory *odb)
 {
 
 	struct stat st;
@@ -310,7 +314,7 @@ static struct commit_graph *load_commit_graph_one(const char *graph_file)
 	if (!open_ok)
 		return NULL;
 
-	g = load_commit_graph_one_fd_st(fd, &st);
+	g = load_commit_graph_one_fd_st(fd, &st, odb);
 
 	if (g)
 		g->filename = xstrdup(graph_file);
@@ -322,12 +326,9 @@ static struct commit_graph *load_commit_graph_v1(struct repository *r,
 						 struct object_directory *odb)
 {
 	char *graph_name = get_commit_graph_filename(odb);
-	struct commit_graph *g = load_commit_graph_one(graph_name);
+	struct commit_graph *g = load_commit_graph_one(graph_name, odb);
 	free(graph_name);
 
-	if (g)
-		g->odb = odb;
-
 	return g;
 }
 
@@ -406,13 +407,11 @@ static struct commit_graph *load_commit_graph_chain(struct repository *r,
 		valid = 0;
 		for (odb = r->objects->odb; odb; odb = odb->next) {
 			char *graph_name = get_split_graph_filename(odb, line.buf);
-			struct commit_graph *g = load_commit_graph_one(graph_name);
+			struct commit_graph *g = load_commit_graph_one(graph_name, odb);
 
 			free(graph_name);
 
 			if (g) {
-				g->odb = odb;
-
 				if (add_graph_to_chain(g, graph_chain, oids, i)) {
 					graph_chain = g;
 					valid = 1;

commit-graph.h

@@ -61,7 +61,8 @@ struct commit_graph {
 	const unsigned char *chunk_base_graphs;
 };
 
-struct commit_graph *load_commit_graph_one_fd_st(int fd, struct stat *st);
+struct commit_graph *load_commit_graph_one_fd_st(int fd, struct stat *st,
+						 struct object_directory *odb);
 struct commit_graph *read_commit_graph_one(struct repository *r,
 					   struct object_directory *odb);
 struct commit_graph *parse_commit_graph(void *graph_map, int fd,

t/helper/test-read-graph.c

@@ -22,7 +22,7 @@ int cmd__read_graph(int argc, const char **argv)
 	if (!open_ok)
 		die_errno(_("Could not open commit-graph '%s'"), graph_name);
 
-	graph = load_commit_graph_one_fd_st(fd, &st);
+	graph = load_commit_graph_one_fd_st(fd, &st, odb);
 	if (!graph)
 		return 1;