Got a clue about the pesky "SYN" messages.

I must not have read libevdev's documentation well enough. Hopefully
this new approach will work better. The risk would be that the
conversion takes too long and properly handling all events leads to an
increasing lag between the physical and the virtual device. I should
probably add an option to let users indicate they would prefer dropping
missed events.

3 files changed, 231 insertions, 275 deletions

diff --git a/src/device/physical/physical_device.c b/src/device/physical/physical_device.c
new file mode 100644
index 0000000..7023791
--- /dev/null
+++ b/src/device/physical/physical_device.c
@@ -0,0 +1,231 @@
+/**** POSIX *******************************************************************/
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+
+/**** LIBEVDEV ****************************************************************/
+#include <libevdev/libevdev.h>
+
+/**** RELABSD *****************************************************************/
+#include <relabsd/debug.h>
+
+/******************************************************************************/
+/**** LOCAL FUNCTIONS *********************************************************/
+/******************************************************************************/
+/*
+ * Ensures that the input device has enabled the EV_REL axes mentioned
+ * in the configuration file.
+ *
+ * Returns -1 on (fatal) error,
+ *         0 all configured axes are accounted for.
+ */
+static int check_for_axes
+(
+   const struct libevdev * const dev,
+   const struct relabsd_config * const conf
+)
+{
+   int i, device_is_valid;
+   unsigned int rel_code;
+
+   device_is_valid = 1;
+
+   for (i = RELABSD_VALID_AXES_COUNT; i --> 0;)
+   {
+      if (conf->axis[i].enabled)
+      {
+         rel_code = relabsd_axis_to_rel((enum relabsd_axis) i);
+
+         if (!libevdev_has_event_code(dev, EV_REL, rel_code))
+         {
+            RELABSD_FATAL
+            (
+               "Input device has no relative %s axis, yet the configuration "
+               "file asks to convert it.",
+               relabsd_axis_to_name((enum relabsd_axis) i)
+            );
+
+            device_is_valid = 0;
+         }
+      }
+   }
+
+   return (device_is_valid - 1);
+}
+
+/*
+ * Ensures that the input device is compatible with the config file.
+ *
+ * Returns -1 on (fatal) error,
+ *         0 is the device is compatible.
+ */
+static int device_is_compatible
+(
+   const struct libevdev * const dev,
+   const struct relabsd_config * const conf
+)
+{
+
+
+   return 0;
+}
+
+/******************************************************************************/
+/**** EXPORTED FUNCTIONS ******************************************************/
+/******************************************************************************/
+int relabsd_physical_device_compatibility_test
+(
+   const struct relabsd_physical_device device [const restrict static 1],
+   const struct relabsd_parameters parameters [const restrict static 0],
+   const int verbose
+)
+{
+   if (!libevdev_has_event_type(device->libevdev, EV_REL))
+   {
+      RELABSD_S_FATAL("The physical device has no relative axes.");
+
+      return -1;
+   }
+
+   if
+   (
+      (parameters != (const struct relabsd_parameters *) NULL)
+      && (check_for_axes(device->libevdev, parameters, verbose) < 0)
+   )
+   {
+      RELABSD_S_FATAL
+      (
+         "Issue with the physical device's axes (or lack thereof), or their"
+         " compatibility with the requested configuration."
+      );
+
+      return -2;
+   }
+
+   return 0;
+}
+
+int relabsd_physical_device_open
+(
+   const char filename [const restrict static 1],
+   struct relabsd_physical_device device [const restrict static 1]
+)
+{
+   int err;
+
+   RELABSD_S_DEBUG(RELABSD_DEBUG_PROGRAM_FLOW, "Opening physical device...");
+
+   errno = 0;
+   device->file = open(filename, O_RDONLY);
+   device->is_late = 0;
+
+   if (device->file == -1)
+   {
+      RELABSD_FATAL
+      (
+         "Could not open physical device '%s' in read only mode: %s.",
+         filename,
+         strerror(errno)
+      );
+
+      return -1;
+   }
+
+   err = libevdev_new_from_fd(device->file, &(device->libevdev));
+
+   if (err != 0)
+   {
+      RELABSD_FATAL
+      (
+         "libevdev could not open physical device '%s': %s.",
+         filename,
+         strerror(-err)
+      );
+
+      close(device->file);
+
+      return -1;
+   }
+
+   return 0;
+}
+
+void relabsd_physical_device_close
+(
+   const struct relabsd_physical_device device [const restrict static 1]
+)
+{
+   RELABSD_S_DEBUG(RELABSD_DEBUG_PROGRAM_FLOW, "Closing input device...");
+
+   libevdev_free(device->libevdev);
+
+   errno = 0;
+
+   if (close(device->file) == -1)
+   {
+      RELABSD_ERROR
+      (
+         "Could not properly close the input device: %s.",
+         strerror(errno)
+      );
+   }
+}
+
+int relabsd_physical_device_read
+(
+   const struct relabsd_physical_device device [const restrict static 1],
+   unsigned int input_type [const restrict static 1],
+   unsigned int input_code [const restrict static 1],
+   int input_value [const restrict static 1]
+)
+{
+   int returned_code;
+   struct input_event event;
+
+   returned_code =
+      libevdev_next_event
+      (
+         device->libevdev,
+         device->is_late ? LIBEVDEV_READ_FLAG_SYNC : LIBEVDEV_READ_FLAG_NORMAL,
+         &event
+      );
+
+   switch (returned_code)
+   {
+      case LIBEVDEV_READ_STATUS_SUCCESS:
+         RELABSD_DEBUG
+         (
+            RELABSD_DEBUG_REAL_EVENTS,
+            "Valid event received: {type = %s; code = %s; value = %d}.",
+             libevdev_event_type_get_name(event.type),
+             libevdev_event_code_get_name(event.type, event.code),
+             event.value
+         );
+
+         *input_type = event.type;
+         *input_code = event.code;
+         *input_value = event.value;
+
+         return 1;
+
+      case LIBEVDEV_READ_STATUS_SYNC:
+         /* There are old events waiting to be read. */
+         device->is_late = 1;
+
+         return 0;
+
+      case -EAGAIN:
+         device->is_late = 0;
+
+         return -1;
+   }
+}
+
+int relabsd_physical_device_is_late
+(
+   const struct relabsd_physical_device device [const restrict static 1]
+)
+{
+   return device->is_late;
+}
diff --git a/src/device/physical_device.c b/src/device/physical_device.c
deleted file mode 100644
index 7e365da..0000000
--- a/src/device/physical_device.c
+++ /dev/null
@@ -1,275 +0,0 @@
-/**** RELABSD *****************************************************************/
-#include <errno.h>
-#include <fcntl.h>
-#include <string.h>
-#include <unistd.h>
-
-/**** LIBEVDEV ****************************************************************/
-#include <libevdev/libevdev.h>
-
-/**** RELABSD *****************************************************************/
-#include <relabsd/debug.h>
-
-/*
- * Ensures that the input device has enabled the EV_REL axes mentioned
- * in the configuration file.
- *
- * Returns -1 on (fatal) error,
- *         0 all configured axes are accounted for.
- */
-static int check_for_axes
-(
-   const struct libevdev * const dev,
-   const struct relabsd_config * const conf
-)
-{
-   int i, device_is_valid;
-   unsigned int rel_code;
-
-   device_is_valid = 1;
-
-   for (i = RELABSD_VALID_AXES_COUNT; i --> 0;)
-   {
-      if (conf->axis[i].enabled)
-      {
-         rel_code = relabsd_axis_to_rel((enum relabsd_axis) i);
-
-         if (!libevdev_has_event_code(dev, EV_REL, rel_code))
-         {
-            RELABSD_FATAL
-            (
-               "Input device has no relative %s axis, yet the configuration "
-               "file asks to convert it.",
-               relabsd_axis_to_name((enum relabsd_axis) i)
-            );
-
-            device_is_valid = 0;
-         }
-      }
-   }
-
-   return (device_is_valid - 1);
-}
-
-/*
- * Ensures that the input device is compatible with the config file.
- *
- * Returns -1 on (fatal) error,
- *         0 is the device is compatible.
- */
-static int device_is_compatible
-(
-   const struct libevdev * const dev,
-   const struct relabsd_config * const conf
-)
-{
-   if (!libevdev_has_event_type(dev, EV_REL))
-   {
-      RELABSD_S_FATAL("Input device has no relative axis.");
-
-      return -1;
-   }
-
-   if (check_for_axes(dev, conf) < 0)
-   {
-      return -1;
-   }
-
-   return 0;
-}
-
-int relabsd_physical_device_open
-(
-   struct relabsd_physical_device * const input,
-   const struct relabsd_config * const conf
-)
-{
-   RELABSD_S_DEBUG(RELABSD_DEBUG_PROGRAM_FLOW, "Opening input device...");
-
-   input->fd = open(conf->input_file, O_RDONLY);
-
-   if (input->fd < 0)
-   {
-      RELABSD_FATAL
-      (
-         "Could not open device '%s' in read only mode: %s.",
-         conf->input_file,
-         strerror(errno)
-      );
-
-      return -1;
-   }
-
-   if
-   (
-      libevdev_new_from_fd(input->fd, &(input->dev)) < 0
-   )
-   {
-      RELABSD_FATAL
-      (
-         "libevdev could not open '%s': %s.",
-         conf->input_file,
-         strerror(errno)
-      );
-
-      close(input->fd);
-
-      return -1;
-   }
-
-   if (device_is_compatible(input->dev, conf) < 0)
-   {
-      return -1;
-   }
-
-   return 0;
-}
-
-void relabsd_physical_device_close (const struct relabsd_physical_device * const input)
-{
-   RELABSD_S_DEBUG(RELABSD_DEBUG_PROGRAM_FLOW, "Closing input device...");
-
-   libevdev_free(input->dev);
-   close(input->fd);
-}
-
-int relabsd_physical_device_read
-(
-   const struct relabsd_physical_device * const input,
-   unsigned int * const input_type,
-   unsigned int * const input_code,
-   int * const input_value
-)
-{
-   int rc;
-   struct input_event event;
-
-   /*
-   if (libevdev_has_event_pending(input->dev) == 0)
-   {
-      return -1;
-   }
-   */
-   rc =
-      libevdev_next_event
-      (
-         input->dev,
-         (LIBEVDEV_READ_FLAG_NORMAL | LIBEVDEV_READ_FLAG_BLOCKING),
-         &event
-      );
-
-   /* TODO: Look into LIBEVDEV_READ_STATUS_SYNC, handle it. */
-   /*
-   if (rc == LIBEVDEV_READ_STATUS_SYNC)
-   {
-      handle_syn_dropped(input->dev);
-   }
-   else
-   */
-   if (rc != LIBEVDEV_READ_STATUS_SUCCESS)
-   {
-      RELABSD_WARNING("[INPUT] Could not get next event: %s.", strerror(-rc));
-
-      return -1;
-   }
-
-   RELABSD_DEBUG
-   (
-      RELABSD_DEBUG_REAL_EVENTS,
-      "Valid event received: {type = %s; code = %s; value = %d}.",
-       libevdev_event_type_get_name(event.type),
-       libevdev_event_code_get_name(event.type, event.code),
-       event.value
-   );
-
-   *input_type = event.type;
-   *input_code = event.code;
-   *input_value = event.value;
-
-   return 0;
-}
-
-int relabsd_physical_device_wait_for_next_event
-(
-   const struct relabsd_physical_device * const input,
-   const struct relabsd_config * const config
-)
-{
-   int ready_fds;
-   const int old_errno = errno;
-   fd_set ready_to_read;
-   struct timeval curr_timeout;
-
-   FD_ZERO(&ready_to_read);
-   FD_SET(input->fd, &ready_to_read);
-
-   /* call to select may alter timeout */
-   memcpy
-   (
-      (void *) &(curr_timeout),
-      (const void *) &(config->timeout),
-      sizeof(struct timeval)
-   );
-
-   errno = 0;
-
-   RELABSD_S_ERROR
-   (
-      "Waiting for input to be ready..."
-   );
-
-   ready_fds = select
-   (
-      (input->fd + 1),
-      &ready_to_read,
-      (fd_set *) NULL,
-      (fd_set *) NULL,
-      (input->timed_out) ? NULL : &(curr_timeout)
-   );
-
-   if (errno != 0)
-   {
-      RELABSD_ERROR
-      (
-         "Unable to wait for timeout: %s (errno: %d).",
-         strerror(errno),
-         errno
-      );
-
-      if (errno == EINTR)
-      {
-         /* Signal interruption? */
-      }
-      else
-      {
-         /* TODO: error message */
-      }
-
-      errno = old_errno;
-
-      return -1;
-   }
-
-   if (ready_fds == -1)
-   {
-      /* TODO: error message */
-
-      RELABSD_S_ERROR
-      (
-         "Unable to wait for timeout, yet errno was not set to anything."
-      );
-
-      errno = old_errno;
-
-      return -1;
-   }
-
-   RELABSD_ERROR
-   (
-      "Input is ready, ready_fds = %d", ready_fds
-   );
-
-   errno = old_errno;
-
-   return ready_fds;
-}
diff --git a/src/device/virtual_device.c b/src/device/virtual/virtual_device.c
index 19d1097..19d1097 100644
--- a/src/device/virtual_device.c
+++ b/src/device/virtual/virtual_device.c