utils: backport set_stdfds()

src/lxc/utils.c

@@ -1365,3 +1365,25 @@ int safe_mount(const char *src, const char *dest, const char *fstype,
 
 	return 0;
 }
+
+int set_stdfds(int fd)
+{
+	int ret;
+
+	if (fd < 0)
+		return -1;
+
+	ret = dup2(fd, STDIN_FILENO);
+	if (ret < 0)
+		return -1;
+
+	ret = dup2(fd, STDOUT_FILENO);
+	if (ret < 0)
+		return -1;
+
+	ret = dup2(fd, STDERR_FILENO);
+	if (ret < 0)
+		return -1;
+
+	return 0;
+}

src/lxc/utils.h

@@ -294,4 +294,5 @@ int null_stdfds(void);
 
 int safe_mount(const char *src, const char *dest, const char *fstype,
 		unsigned long flags, const void *data, const char *rootfs);
+int set_stdfds(int fd);
 #endif /* __LXC_UTILS_H */