lib/pwdutils: add xgetlogin()

Signed-off-by: Karel Zak <kzak@redhat.com>

include/pwdutils.h

@@ -5,6 +5,7 @@
 #include <pwd.h>
 
 extern struct passwd *xgetpwnam(const char *username, char **pwdbuf);
+extern char *xgetlogin(void);
 
 #endif /* UTIL_LINUX_PWDUTILS_H */
 

lib/pwdutils.c

@@ -36,11 +36,39 @@ failed:
 	return NULL;
 }
 
+char *xgetlogin(void)
+{
+	struct passwd *pw = NULL;
+	uid_t ruid;
+	char *user;
+
+	user = getlogin();
+	if (user)
+		return xstrdup(user);
+
+	/* GNU Hurd implementation has an extension where a process can exist in a
+	 * non-conforming environment, and thus be outside the realms of POSIX
+	 * process identifiers; on this platform, getuid() fails with a status of
+	 * (uid_t)(-1) and sets errno if a program is run from a non-conforming
+	 * environment.
+	 *
+	 * http://austingroupbugs.net/view.php?id=511
+	 */
+	errno = 0;
+	ruid = getuid();
+
+	if (errno == 0)
+		pw = getpwuid(ruid);
+	if (pw && pw->pw_name && *pw->pw_name)
+		return xstrdup(pw->pw_name);
+
+	return NULL;
+}
 
 #ifdef TEST_PROGRAM
 int main(int argc, char *argv[])
 {
-	char *pwdbuf = NULL;
+	char *buf = NULL;
 	struct passwd *pwd = NULL;
 
 	if (argc != 2) {
@@ -48,7 +76,7 @@ int main(int argc, char *argv[])
 		return EXIT_FAILURE;
 	}
 
-	pwd = xgetpwnam(argv[1], &pwdbuf);
+	pwd = xgetpwnam(argv[1], &buf);
 	if (!pwd)
 		err(EXIT_FAILURE, "failed to get %s pwd entry", argv[1]);
 
@@ -58,7 +86,11 @@ int main(int argc, char *argv[])
 	printf("GECO:     %s\n", pwd->pw_gecos);
 
 	free(pwd);
-	free(pwdbuf);
+	free(buf);
+
+	printf("Current:  %s\n", (buf = xgetlogin()));
+	free(buf);
+
 	return EXIT_SUCCESS;
 }
 #endif /* TEST_PROGRAM */