config: warn on inaccessible files

Before reading a config file, we check "!access(path, R_OK)"
to make sure that the file exists and is readable. If it's
not, then we silently ignore it.

For the case of ENOENT, this is fine, as the presence of the
file is optional. For other cases, though, it may indicate a
configuration error (e.g., not having permissions to read
the file). Let's print a warning in these cases to let the
user know.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/config.c

@@ -396,8 +396,8 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 			 */
 			die("$HOME not set");
 
-		if (access(user_config, R_OK) &&
-		    xdg_config && !access(xdg_config, R_OK))
+		if (access_or_warn(user_config, R_OK) &&
+		    xdg_config && !access_or_warn(xdg_config, R_OK))
 			given_config_file = xdg_config;
 		else
 			given_config_file = user_config;

config.c

@@ -60,7 +60,7 @@ static int handle_path_include(const char *path, struct config_include_data *inc
 		path = buf.buf;
 	}
 
-	if (!access(path, R_OK)) {
+	if (!access_or_warn(path, R_OK)) {
 		if (++inc->depth > MAX_INCLUDE_DEPTH)
 			die(include_depth_advice, MAX_INCLUDE_DEPTH, path,
 			    cf && cf->name ? cf->name : "the command line");
@@ -939,23 +939,23 @@ int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 
 	home_config_paths(&user_config, &xdg_config, "config");
 
-	if (git_config_system() && !access(git_etc_gitconfig(), R_OK)) {
+	if (git_config_system() && !access_or_warn(git_etc_gitconfig(), R_OK)) {
 		ret += git_config_from_file(fn, git_etc_gitconfig(),
 					    data);
 		found += 1;
 	}
 
-	if (xdg_config && !access(xdg_config, R_OK)) {
+	if (xdg_config && !access_or_warn(xdg_config, R_OK)) {
 		ret += git_config_from_file(fn, xdg_config, data);
 		found += 1;
 	}
 
-	if (user_config && !access(user_config, R_OK)) {
+	if (user_config && !access_or_warn(user_config, R_OK)) {
 		ret += git_config_from_file(fn, user_config, data);
 		found += 1;
 	}
 
-	if (repo_config && !access(repo_config, R_OK)) {
+	if (repo_config && !access_or_warn(repo_config, R_OK)) {
 		ret += git_config_from_file(fn, repo_config, data);
 		found += 1;
 	}

git-compat-util.h

@@ -604,6 +604,9 @@ int rmdir_or_warn(const char *path);
  */
 int remove_or_warn(unsigned int mode, const char *path);
 
+/* Call access(2), but warn for any error besides ENOENT. */
+int access_or_warn(const char *path, int mode);
+
 /* Get the passwd entry for the UID of the current process. */
 struct passwd *xgetpwuid_self(void);
 

wrapper.c

@@ -403,6 +403,14 @@ int remove_or_warn(unsigned int mode, const char *file)
 	return S_ISGITLINK(mode) ? rmdir_or_warn(file) : unlink_or_warn(file);
 }
 
+int access_or_warn(const char *path, int mode)
+{
+	int ret = access(path, mode);
+	if (ret && errno != ENOENT)
+		warning(_("unable to access '%s': %s"), path, strerror(errno));
+	return ret;
+}
+
 struct passwd *xgetpwuid_self(void)
 {
 	struct passwd *pw;