config: Introduce functions to write non-standard file

Introduce two new functions corresponding to "git_config_set" and
"git_config_set_multivar" to write a non-standard configuration file.
Expose these new functions in cache.h for other git programs to use.

Helped-by: Jeff King <peff@peff.net>
Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -1051,9 +1051,11 @@ extern int git_config_bool(const char *, const char *);
 extern int git_config_maybe_bool(const char *, const char *);
 extern int git_config_string(const char **, const char *, const char *);
 extern int git_config_pathname(const char **, const char *, const char *);
+extern int git_config_set_in_file(const char *, const char *, const char *);
 extern int git_config_set(const char *, const char *);
 extern int git_config_parse_key(const char *, char **, int *);
 extern int git_config_set_multivar(const char *, const char *, const char *, int);
+extern int git_config_set_multivar_in_file(const char *, const char *, const char *, const char *, int);
 extern int git_config_rename_section(const char *, const char *);
 extern const char *git_etc_gitconfig(void);
 extern int check_repository_format_version(const char *var, const char *value, void *cb);

config.c

@@ -1073,6 +1073,12 @@ contline:
 	return offset;
 }
 
+int git_config_set_in_file(const char *config_filename,
+			const char *key, const char *value)
+{
+	return git_config_set_multivar_in_file(config_filename, key, value, NULL, 0);
+}
+
 int git_config_set(const char *key, const char *value)
 {
 	return git_config_set_multivar(key, value, NULL, 0);
@@ -1170,19 +1176,14 @@ out_free_ret_1:
  * - the config file is removed and the lock file rename()d to it.
  *
  */
-int git_config_set_multivar(const char *key, const char *value,
-	const char *value_regex, int multi_replace)
+int git_config_set_multivar_in_file(const char *config_filename,
+				const char *key, const char *value,
+				const char *value_regex, int multi_replace)
 {
 	int fd = -1, in_fd;
 	int ret;
-	char *config_filename;
 	struct lock_file *lock = NULL;
 
-	if (config_exclusive_filename)
-		config_filename = xstrdup(config_exclusive_filename);
-	else
-		config_filename = git_pathdup("config");
-
 	/* parse-key returns negative; flip the sign to feed exit(3) */
 	ret = 0 - git_config_parse_key(key, &store.key, &store.baselen);
 	if (ret)
@@ -1359,7 +1360,6 @@ int git_config_set_multivar(const char *key, const char *value,
 out_free:
 	if (lock)
 		rollback_lock_file(lock);
-	free(config_filename);
 	return ret;
 
 write_err_out:
@@ -1368,6 +1368,24 @@ write_err_out:
 
 }
 
+int git_config_set_multivar(const char *key, const char *value,
+			const char *value_regex, int multi_replace)
+{
+	const char *config_filename;
+	char *buf = NULL;
+	int ret;
+
+	if (config_exclusive_filename)
+		config_filename = config_exclusive_filename;
+	else
+		config_filename = buf = git_pathdup("config");
+
+	ret = git_config_set_multivar_in_file(config_filename, key, value,
+					value_regex, multi_replace);
+	free(buf);
+	return ret;
+}
+
 static int section_name_match (const char *buf, const char *name)
 {
 	int i = 0, j = 0, dot = 0;