diff --git a/Android.bp b/Android.bp
index 98b4010..b495dac 100644
--- a/Android.bp
+++ b/Android.bp
@@ -35,7 +35,6 @@
         "netlink_msg.c",
         "ring.c",
         "setif.c",
-        "tun.c",
         "translate.c",
     ],
 }
diff --git a/clatd.c b/clatd.c
index d68dc05..d332e1e 100644
--- a/clatd.c
+++ b/clatd.c
@@ -355,7 +355,6 @@
  */
 void configure_interface(const char *uplink_interface, const char *plat_prefix, const char *v4_addr,
                          const char *v6_addr, struct tun_data *tunnel, unsigned net_id) {
-  int error;
 
   if (!read_config("/system/etc/clatd.conf", uplink_interface, plat_prefix, net_id)) {
     logmsg(ANDROID_LOG_FATAL, "read_config failed");
@@ -381,18 +380,6 @@
     logmsg(ANDROID_LOG_WARN, "ipv4mtu now set to = %d", Global_Clatd_Config.ipv4mtu);
   }
 
-  error = tun_alloc(tunnel->device4, tunnel->fd4, sizeof(tunnel->device4));
-  if (error < 0) {
-    logmsg(ANDROID_LOG_FATAL, "tun_alloc/4 failed: %s", strerror(errno));
-    exit(1);
-  }
-
-  error = set_nonblocking(tunnel->fd4);
-  if (error < 0) {
-    logmsg(ANDROID_LOG_FATAL, "set_nonblocking failed: %s", strerror(errno));
-    exit(1);
-  }
-
   configure_tun_ip(tunnel, v4_addr);
 
   if (!configure_clat_ipv6_address(tunnel, uplink_interface, v6_addr)) {
@@ -497,14 +484,3 @@
     }
   }
 }
-
-/* function: parse_unsigned
- * parses a string as a decimal/hex/octal unsigned integer
- *   str - the string to parse
- *   out - the unsigned integer to write to, gets clobbered on failure
- */
-int parse_unsigned(const char *str, unsigned *out) {
-  char *end_ptr;
-  *out = strtoul(str, &end_ptr, 0);
-  return *str && !*end_ptr;
-}
diff --git a/clatd.h b/clatd.h
index f7f7315..d3869bf 100644
--- a/clatd.h
+++ b/clatd.h
@@ -18,6 +18,7 @@
 #ifndef __CLATD_H__
 #define __CLATD_H__
 
+#include <stdlib.h>
 #include <sys/uio.h>
 
 struct tun_data;
@@ -45,6 +46,27 @@
 void configure_interface(const char *uplink_interface, const char *plat_prefix, const char *v4_addr,
                          const char *v6, struct tun_data *tunnel, unsigned net_id);
 void event_loop(struct tun_data *tunnel);
-int parse_unsigned(const char *str, unsigned *out);
+
+/* function: parse_int
+ * parses a string as a decimal/hex/octal signed integer
+ *   str - the string to parse
+ *   out - the signed integer to write to, gets clobbered on failure
+ */
+static inline int parse_int(const char *str, int *out) {
+  char *end_ptr;
+  *out = strtol(str, &end_ptr, 0);
+  return *str && !*end_ptr;
+}
+
+/* function: parse_unsigned
+ * parses a string as a decimal/hex/octal unsigned integer
+ *   str - the string to parse
+ *   out - the unsigned integer to write to, gets clobbered on failure
+ */
+static inline int parse_unsigned(const char *str, unsigned *out) {
+  char *end_ptr;
+  *out = strtoul(str, &end_ptr, 0);
+  return *str && !*end_ptr;
+}
 
 #endif /* __CLATD_H__ */
diff --git a/clatd_microbenchmark.c b/clatd_microbenchmark.c
index 15a0376..ea58a8a 100644
--- a/clatd_microbenchmark.c
+++ b/clatd_microbenchmark.c
@@ -200,12 +200,10 @@
   close(fd);
 
   fd = setup_tun();
-  set_nonblocking(fd);
   benchmark("No read", fd, sock, NUMPACKETS, 0, payload, sizeof(payload), payload_sum);
   close(fd);
 
   fd = setup_tun();
-  set_nonblocking(fd);
   benchmark("Nonblocking", fd, sock, NUMPACKETS, 1, payload, sizeof(payload), payload_sum);
   close(fd);
 
diff --git a/main.c b/main.c
index 54d12d1..9e796fd 100644
--- a/main.c
+++ b/main.c
@@ -46,6 +46,7 @@
   printf("-6 [IPv6 address]\n");
   printf("-n [NetId]\n");
   printf("-m [socket mark]\n");
+  printf("-t [tun file descriptor number]\n");
 }
 
 /* function: main
@@ -55,12 +56,12 @@
   struct tun_data tunnel;
   int opt;
   char *uplink_interface = NULL, *plat_prefix = NULL, *net_id_str = NULL, *mark_str = NULL;
-  char *v4_addr = NULL, *v6_addr = NULL;
+  char *v4_addr = NULL, *v6_addr = NULL, *tunfd_str = NULL;
   unsigned net_id = NETID_UNSET;
   uint32_t mark   = MARK_UNSET;
   unsigned len;
 
-  while ((opt = getopt(argc, argv, "i:p:4:6:n:m:h")) != -1) {
+  while ((opt = getopt(argc, argv, "i:p:4:6:n:m:t:h")) != -1) {
     switch (opt) {
       case 'i':
         uplink_interface = optarg;
@@ -80,6 +81,9 @@
       case 'm':
         mark_str = optarg;
         break;
+      case 't':
+        tunfd_str = optarg;
+        break;
       case 'h':
         print_help();
         exit(0);
@@ -104,6 +108,15 @@
     exit(1);
   }
 
+  if (tunfd_str != NULL && !parse_int(tunfd_str, &tunnel.fd4)) {
+    logmsg(ANDROID_LOG_FATAL, "invalid tunfd %s", tunfd_str);
+    exit(1);
+  }
+  if (!tunnel.fd4) {
+    logmsg(ANDROID_LOG_FATAL, "no tunfd specified on commandline.");
+    exit(1);
+  }
+
   len = snprintf(tunnel.device4, sizeof(tunnel.device4), "%s%s", DEVICEPREFIX, uplink_interface);
   if (len >= sizeof(tunnel.device4)) {
     logmsg(ANDROID_LOG_FATAL, "interface name too long '%s'", tunnel.device4);
@@ -124,13 +137,6 @@
   // keeps only admin capability
   set_capability(1 << CAP_NET_ADMIN);
 
-  // we can create tun devices as non-root because we're in the VPN group.
-  tunnel.fd4 = tun_open();
-  if (tunnel.fd4 < 0) {
-    logmsg(ANDROID_LOG_FATAL, "tun_open4 failed: %s", strerror(errno));
-    exit(1);
-  }
-
   // When run from netd, the environment variable ANDROID_DNS_MODE is set to
   // "local", but that only works for the netd process itself. Removing the
   // following line causes XLAT failure in permissive mode.
diff --git a/tun.c b/tun.c
index 7ecbf2c..e2f1342 100644
--- a/tun.c
+++ b/tun.c
@@ -21,20 +21,19 @@
 #include <linux/if_tun.h>
 #include <string.h>
 #include <sys/ioctl.h>
-#include <sys/uio.h>
 #include <unistd.h>
 
 #include "common.h"
 
 /* function: tun_open
- * tries to open the tunnel device
+ * tries to open the tunnel device in non-blocking mode
  */
 int tun_open() {
   int fd;
 
-  fd = open("/dev/tun", O_RDWR | O_CLOEXEC);
+  fd = open("/dev/tun", O_RDWR | O_NONBLOCK | O_CLOEXEC);
   if (fd < 0) {
-    fd = open("/dev/net/tun", O_RDWR | O_CLOEXEC);
+    fd = open("/dev/net/tun", O_RDWR | O_NONBLOCK | O_CLOEXEC);
   }
 
   return fd;
@@ -65,25 +64,3 @@
   strlcpy(dev, ifr.ifr_name, len);
   return 0;
 }
-
-/* function: set_nonblocking
- * sets a filedescriptor to non-blocking mode
- * fd - the filedescriptor
- * returns: 0 on success, -1 on failure
- */
-int set_nonblocking(int fd) {
-  int flags = fcntl(fd, F_GETFL);
-  if (flags == -1) {
-    return flags;
-  }
-  return fcntl(fd, F_SETFL, flags | O_NONBLOCK);
-}
-
-/* function: send_tun
- * sends a clat_packet to a tun interface
- * fd      - the tun filedescriptor
- * out     - the packet to send
- * iov_len - the number of entries in the clat_packet
- * returns: number of bytes read on success, -1 on failure
- */
-int send_tun(int fd, clat_packet out, int iov_len) { return writev(fd, out, iov_len); }
diff --git a/tun.h b/tun.h
index 95650fa..05f62c1 100644
--- a/tun.h
+++ b/tun.h
@@ -18,7 +18,10 @@
 #ifndef __TUN_H__
 #define __TUN_H__
 
+#include <fcntl.h>
 #include <linux/if.h>
+#include <sys/uio.h>
+#include <unistd.h>
 
 #include "common.h"
 #include "ring.h"
@@ -29,9 +32,19 @@
   struct packet_ring ring;
 };
 
+// tun_open and tun_alloc are defined in tun.c and only used by clatd_microbenchmark.c
 int tun_open();
 int tun_alloc(char *dev, int fd, size_t len);
-int send_tun(int fd, clat_packet out, int iov_len);
-int set_nonblocking(int fd);
+
+/* function: send_tun
+ * sends a clat_packet to a tun interface
+ * fd      - the tun filedescriptor
+ * out     - the packet to send
+ * iov_len - the number of entries in the clat_packet
+ * returns: number of bytes read on success, -1 on failure
+ */
+static inline int send_tun(int fd, clat_packet out, int iov_len) {
+  return writev(fd, out, iov_len);
+}
 
 #endif