Fix compatibility with TAP-Win32 9.0.0.21 and later.

Tinc was a bit sloppy writing packets to the TAP-Win32 device using
overlapped I/O. It worked with older versions of the driver, but it
caused lots of dropped packets with newer versions of the driver (that
use the NDIS 6 API).

diff --git a/src/mingw/device.c b/src/mingw/device.c
index 235e0fd..49b833a 100644 (file)
--- a/src/mingw/device.c
+++ b/src/mingw/device.c
@@ -43,11 +43,12 @@ static uint64_t device_total_in = 0;
 static uint64_t device_total_out = 0;
 
 extern char *myport;
+OVERLAPPED r_overlapped;
+OVERLAPPED w_overlapped;
 
 static DWORD WINAPI tapreader(void *bla) {
        int status;
        DWORD len;
-       OVERLAPPED overlapped;
        vpn_packet_t packet;
        int errors = 0;
 
@@ -55,19 +56,17 @@ static DWORD WINAPI tapreader(void *bla) {
 
        /* Read from tap device and send to parent */
 
-       overlapped.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
+       r_overlapped.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
 
        for(;;) {
-               overlapped.Offset = 0;
-               overlapped.OffsetHigh = 0;
-               ResetEvent(overlapped.hEvent);
+               ResetEvent(r_overlapped.hEvent);
 
-               status = ReadFile(device_handle, packet.data, MTU, &len, &overlapped);
+               status = ReadFile(device_handle, packet.data, MTU, &len, &r_overlapped);
 
                if(!status) {
                        if(GetLastError() == ERROR_IO_PENDING) {
-                               WaitForSingleObject(overlapped.hEvent, INFINITE);
-                               if(!GetOverlappedResult(device_handle, &overlapped, &len, FALSE))
+                               WaitForSingleObject(r_overlapped.hEvent, INFINITE);
+                               if(!GetOverlappedResult(device_handle, &r_overlapped, &len, FALSE))
                                        continue;
                        } else {
                                logger(LOG_ERR, "Error while reading from %s %s: %s", device_info,
@@ -201,6 +200,11 @@ static bool setup_device(void) {
                overwrite_mac = 1;
        }
 
+       /* Create overlapped events for tap I/O */
+
+       r_overlapped.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
+       w_overlapped.hEvent = CreateEvent(NULL, TRUE, TRUE, NULL);
+
        /* Start the tap reader */
 
        thread = CreateThread(NULL, 0, tapreader, NULL, 0, NULL);
@@ -235,14 +239,48 @@ static bool read_packet(vpn_packet_t *packet) {
 
 static bool write_packet(vpn_packet_t *packet) {
        DWORD lenout;
-       OVERLAPPED overlapped = {0};
+       static vpn_packet_t queue;
 
        ifdebug(TRAFFIC) logger(LOG_DEBUG, "Writing packet of %d bytes to %s",
                           packet->len, device_info);
 
-       if(!WriteFile(device_handle, packet->data, packet->len, &lenout, &overlapped)) {
-               logger(LOG_ERR, "Error while writing to %s %s: %s", device_info, device, winerror(GetLastError()));
-               return false;
+       /* Check if there is something in progress */
+
+       if(queue.len) {
+               DWORD size;
+               BOOL success = GetOverlappedResult(device_handle, &w_overlapped, &size, FALSE);
+               if(success) {
+                       ResetEvent(&w_overlapped);
+                       queue.len = 0;
+               } else {
+                       int err = GetLastError();
+                       if(err != ERROR_IO_INCOMPLETE) {
+                               ifdebug(TRAFFIC) logger(LOG_DEBUG, "Error completing previously queued write: %s", winerror(err));
+                               ResetEvent(&w_overlapped);
+                               queue.len = 0;
+                       } else {
+                               ifdebug(TRAFFIC) logger(LOG_DEBUG, "Previous overlapped write still in progress");
+                               // drop this packet
+                               return true;
+                       }
+               }
+       }
+
+       /* Otherwise, try to write. */
+
+       memcpy(queue.data, packet->data, packet->len);
+
+       if(!WriteFile(device_handle, queue.data, packet->len, &lenout, &w_overlapped)) {
+               int err = GetLastError();
+               if(err != ERROR_IO_PENDING) {
+                       logger(LOG_ERR, "Error while writing to %s %s: %s", device_info, device, winerror(err));
+                       return false;
+               }
+               // Write is being done asynchronously.
+               queue.len = packet->len;
+       } else {
+               // Write was completed immediately.
+               ResetEvent(&w_overlapped);
        }
 
        device_total_out += packet->len;