libusb: implement libusb_pollfds_handle_timeouts

This function tells applications who maintain the pollfds themselves if
they should handle the timeout for each xfer themselves. In FreeBSD, the
timeout for each xfer is handled by kernel and doesn't need a special timer to
do so. Therefore, we return 1 to indicate that it is handled by libusb
internally.

Approved by:    lwhsu (mentor), markj (mentor)
Sponsored by:   The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D51742

lib/libusb/libusb.3

@@ -734,6 +734,14 @@ another thread is already doing so.
 Must be called with the event lock held.
 .Pp
 .Ft int
+.Fn libusb_pollfds_handle_timeouts "libusb_context *ctx"
+This function determines whether applications maintaining libusb events using
+.Fn libusb_get_pollfds
+are responsible for handling timeout events themselves.
+Returns 1 if libusb handles the timeout internally, 0 if the application
+needs to set a dedicated timer to handle it.
+.Pp
+.Ft int
 .Fn libusb_get_next_timeout "libusb_context *ctx" "struct timeval *tv"
 Determine the next internal timeout that libusb needs to handle.
 Returns 0

lib/libusb/libusb.h

@@ -587,6 +587,7 @@ int	libusb_handle_events_completed(libusb_context * ctx, int *completed);
 int	libusb_handle_events_timeout(libusb_context * ctx, struct timeval *tv);
 int	libusb_handle_events(libusb_context * ctx);
 int	libusb_handle_events_locked(libusb_context * ctx, struct timeval *tv);
+int	libusb_pollfds_handle_timeouts(libusb_context *ctx);
 int	libusb_get_next_timeout(libusb_context * ctx, struct timeval *tv);
 void	libusb_set_pollfd_notifiers(libusb_context * ctx, libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb, void *user_data);
 const struct libusb_pollfd **libusb_get_pollfds(libusb_context *ctx);

lib/libusb/libusb10_io.c

@@ -422,6 +422,12 @@ libusb_get_next_timeout(libusb_context *ctx, struct timeval *tv)
 	return (0);
 }
 
+int
+libusb_pollfds_handle_timeouts(libusb_context *ctx)
+{
+	return (1);
+}
+
 void
 libusb_set_pollfd_notifiers(libusb_context *ctx,
     libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,