Merge branch 'jk/info-alternates-fix' into maint

A regression fix for 2.11 that made the code to read the list of
alternate object stores overrun the end of the string.

* jk/info-alternates-fix:
  read_info_alternates: warn on non-trivial errors
  read_info_alternates: read contents into strbuf

sha1_file.c

@@ -422,7 +422,7 @@ static const char *parse_alt_odb_entry(const char *string,
 	return end;
 }
 
-static void link_alt_odb_entries(const char *alt, int len, int sep,
+static void link_alt_odb_entries(const char *alt, int sep,
 				 const char *relative_base, int depth)
 {
 	struct strbuf objdirbuf = STRBUF_INIT;
@@ -451,28 +451,19 @@ static void link_alt_odb_entries(const char *alt, int len, int sep,
 
 static void read_info_alternates(const char * relative_base, int depth)
 {
-	char *map;
-	size_t mapsz;
-	struct stat st;
 	char *path;
-	int fd;
+	struct strbuf buf = STRBUF_INIT;
 
 	path = xstrfmt("%s/info/alternates", relative_base);
-	fd = git_open(path);
-	free(path);
-	if (fd < 0)
-		return;
-	if (fstat(fd, &st) || (st.st_size == 0)) {
-		close(fd);
+	if (strbuf_read_file(&buf, path, 1024) < 0) {
+		warn_on_fopen_errors(path);
+		free(path);
 		return;
 	}
-	mapsz = xsize_t(st.st_size);
-	map = xmmap(NULL, mapsz, PROT_READ, MAP_PRIVATE, fd, 0);
-	close(fd);
-
-	link_alt_odb_entries(map, mapsz, '\n', relative_base, depth);
 
-	munmap(map, mapsz);
+	link_alt_odb_entries(buf.buf, '\n', relative_base, depth);
+	strbuf_release(&buf);
+	free(path);
 }
 
 struct alternate_object_database *alloc_alt_odb(const char *dir)
@@ -527,7 +518,7 @@ void add_to_alternates_file(const char *reference)
 		if (commit_lock_file(lock))
 			die_errno("unable to move new alternates file into place");
 		if (alt_odb_tail)
-			link_alt_odb_entries(reference, strlen(reference), '\n', NULL, 0);
+			link_alt_odb_entries(reference, '\n', NULL, 0);
 	}
 	free(alts);
 }
@@ -540,7 +531,7 @@ void add_to_alternates_memory(const char *reference)
 	 */
 	prepare_alt_odb();
 
-	link_alt_odb_entries(reference, strlen(reference), '\n', NULL, 0);
+	link_alt_odb_entries(reference, '\n', NULL, 0);
 }
 
 /*
@@ -643,7 +634,7 @@ void prepare_alt_odb(void)
 	if (!alt) alt = "";
 
 	alt_odb_tail = &alt_odb_list;
-	link_alt_odb_entries(alt, strlen(alt), PATH_SEP, NULL, 0);
+	link_alt_odb_entries(alt, PATH_SEP, NULL, 0);
 
 	read_info_alternates(get_object_directory(), 0);
 }