Add iface.[ch]

src/iface.c

@@ -0,0 +1,29 @@
+#include "common.h"
+
+#include "str.h"
+
+#include <sys/ioctl.h>
+#include <net/if.h>
+
+int
+iface_set_mtu(char *dev_name, int mtu)
+{
+    struct ifreq ifr = {
+        .ifr_mtu = mtu,
+    };
+
+    str_cpy(ifr.ifr_name, dev_name, IFNAMSIZ - 1);
+
+    int fd = socket(AF_INET, SOCK_DGRAM, 0);
+
+    if (fd == -1)
+        return -1;
+
+    int ret = ioctl(fd, SIOCSIFMTU, &ifr);
+
+    int err = errno;
+    close(fd);
+    errno = err;
+
+    return ret;
+}