Open the file descriptor of a serial port on POSIX systems exclusively

[libserialport.git] / serialport.c

diff --git a/serialport.c b/serialport.c
index b2e4a7984fdcf2738209bc74cacd60f66c693a9b..51fe0788fc4abd015adc9768d63c9288ac9e0593 100644 (file)
--- a/serialport.c
+++ b/serialport.c
@@ -488,7 +488,7 @@ SP_API enum sp_return sp_open(struct sp_port *port, enum sp_mode flags)
        if (flags & SP_MODE_WRITE)
                desired_access |= GENERIC_WRITE;
 
-       port->hdl = CreateFile(escaped_port_name, desired_access, 0, 0,
+       port->hdl = CreateFileA(escaped_port_name, desired_access, 0, 0,
                         OPEN_EXISTING, flags_and_attributes, 0);
 
        free(escaped_port_name);
@@ -551,6 +551,39 @@ SP_API enum sp_return sp_open(struct sp_port *port, enum sp_mode flags)
 
        if ((port->fd = open(port->name, flags_local)) < 0)
                RETURN_FAIL("open() failed");
+
+       /*
+        * On POSIX in the default case the file descriptor of a serial port
+        * is not opened exclusively. Therefore the settings of a port are
+        * overwritten if the serial port is opened a second time. Windows
+        * opens all serial ports exclusively.
+        * So the idea is to open the serial ports alike in the exclusive mode.
+        *
+        * ioctl(*, TIOCEXCL) defines the file descriptor as exclusive. So all
+        * further open calls on the serial port will fail.
+        *
+        * There is a race condition if two processes open the same serial
+        * port. None of the processes will notice the exclusive ownership of
+        * the other process because ioctl() doesn't return an error code if
+        * the file descriptor is already marked as exclusive.
+        * This can be solved with flock(). It returns an error if the file
+        * descriptor is already locked by another process.
+        */
+#ifdef HAVE_FLOCK
+       if (flock(port->fd, LOCK_EX | LOCK_NB) < 0)
+               RETURN_FAIL("flock() failed");
+#endif
+
+#ifdef TIOCEXCL
+       /*
+        * Before Linux 3.8 ioctl(*, TIOCEXCL) was not implemented and could
+        * lead to EINVAL or ENOTTY.
+        * These errors aren't fatal and can be ignored.
+        */
+       if (ioctl(port->fd, TIOCEXCL) < 0 && errno != EINVAL && errno != ENOTTY)
+               RETURN_FAIL("ioctl() failed");
+#endif
+
 #endif
 
        ret = get_config(port, &data, &config);
@@ -1307,6 +1340,11 @@ SP_API enum sp_return sp_output_waiting(struct sp_port *port)
 {
        TRACE("%p", port);
 
+#ifdef __CYGWIN__
+       /* TIOCOUTQ is not defined in Cygwin headers */
+       RETURN_ERROR(SP_ERR_SUPP,
+                       "Getting output bytes waiting is not supported on Cygwin");
+#else
        CHECK_OPEN_PORT();
 
        DEBUG_FMT("Checking output bytes waiting on port %s", port->name);
@@ -1324,6 +1362,7 @@ SP_API enum sp_return sp_output_waiting(struct sp_port *port)
                RETURN_FAIL("TIOCOUTQ ioctl failed");
        RETURN_INT(bytes_waiting);
 #endif
+#endif
 }
 
 SP_API enum sp_return sp_new_event_set(struct sp_event_set **result_ptr)
@@ -1442,6 +1481,7 @@ SP_API enum sp_return sp_wait(struct sp_event_set *event_set,
        RETURN_OK();
 #else
        struct timeout timeout;
+       int poll_timeout;
        int result;
        struct pollfd *pollfds;
        unsigned int i;
@@ -1472,7 +1512,11 @@ SP_API enum sp_return sp_wait(struct sp_event_set *event_set,
                        break;
                }
 
-               result = poll(pollfds, event_set->count, timeout_remaining_ms(&timeout) || -1);
+               poll_timeout = (int) timeout_remaining_ms(&timeout);
+               if (poll_timeout == 0)
+                       poll_timeout = -1;
+
+               result = poll(pollfds, event_set->count, poll_timeout);
 
                timeout_update(&timeout);
 
@@ -1637,28 +1681,25 @@ static enum sp_return get_config(struct sp_port *port, struct port_data *data,
 
        config->bits = data->dcb.ByteSize;
 
-       if (data->dcb.fParity)
-               switch (data->dcb.Parity) {
-               case NOPARITY:
-                       config->parity = SP_PARITY_NONE;
-                       break;
-               case ODDPARITY:
-                       config->parity = SP_PARITY_ODD;
-                       break;
-               case EVENPARITY:
-                       config->parity = SP_PARITY_EVEN;
-                       break;
-               case MARKPARITY:
-                       config->parity = SP_PARITY_MARK;
-                       break;
-               case SPACEPARITY:
-                       config->parity = SP_PARITY_SPACE;
-                       break;
-               default:
-                       config->parity = -1;
-               }
-       else
+       switch (data->dcb.Parity) {
+       case NOPARITY:
                config->parity = SP_PARITY_NONE;
+               break;
+       case ODDPARITY:
+               config->parity = SP_PARITY_ODD;
+               break;
+       case EVENPARITY:
+               config->parity = SP_PARITY_EVEN;
+               break;
+       case MARKPARITY:
+               config->parity = SP_PARITY_MARK;
+               break;
+       case SPACEPARITY:
+               config->parity = SP_PARITY_SPACE;
+               break;
+       default:
+               config->parity = -1;
+       }
 
        switch (data->dcb.StopBits) {
        case ONESTOPBIT:
@@ -1838,6 +1879,7 @@ static enum sp_return set_config(struct sp_port *port, struct port_data *data,
        DEBUG_FMT("Setting configuration for port %s", port->name);
 
 #ifdef _WIN32
+       BYTE* new_buf;
 
        TRY(await_write_completion(port));
 
@@ -1854,11 +1896,10 @@ static enum sp_return set_config(struct sp_port *port, struct port_data *data,
 
                /* Allocate write buffer for 50ms of data at baud rate. */
                port->write_buf_size = max(config->baudrate / (8 * 20), 1);
-               port->write_buf = realloc(port->write_buf,
-                                         port->write_buf_size);
-
-               if (!port->write_buf)
+               new_buf = realloc(port->write_buf, port->write_buf_size);
+               if (!new_buf)
                        RETURN_ERROR(SP_ERR_MEM, "Allocating write buffer failed");
+               port->write_buf = new_buf;
        }
 
        if (config->bits >= 0)
@@ -2478,17 +2519,17 @@ SP_API char *sp_last_error_message(void)
        TRACE_VOID();
 
 #ifdef _WIN32
-       TCHAR *message;
+       char *message;
        DWORD error = GetLastError();
 
-       DWORD length = FormatMessage(
+       DWORD length = FormatMessageA(
                FORMAT_MESSAGE_ALLOCATE_BUFFER |
                FORMAT_MESSAGE_FROM_SYSTEM |
                FORMAT_MESSAGE_IGNORE_INSERTS,
                NULL,
                error,
                MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
-               (LPTSTR) &message,
+               (LPSTR) &message,
                0, NULL );
 
        if (length >= 2 && message[length - 2] == '\r')