Use FIONREAD to detect if stdin has data, safer than just select()

When handling the stdin redirect workaround we should use FIONREAD to
figure out if there is any data to read.

When there is no more data to read from stdin we remove the watcher from
internal bookkeeping but allow the callback to run one last time so it
can detect a short read.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/uev.c

@@ -26,6 +26,7 @@
 #include <fcntl.h>		/* O_CLOEXEC */
 #include <string.h>		/* memset() */
 #include <sys/epoll.h>
+#include <sys/ioctl.h>
 #include <sys/select.h>		/* for select() workaround */
 #include <sys/signalfd.h>	/* struct signalfd_siginfo */
 #include <unistd.h>		/* close(), read() */
@@ -62,11 +63,15 @@ static int has_data(int fd)
 {
 	struct timeval timeout = { 0, 0 };
 	fd_set fds;
+	int n = 0;
 
 	FD_ZERO(&fds);
 	FD_SET(fd, &fds);
 
-	return select(1, &fds, NULL, NULL, &timeout) > 0;
+	if (select(1, &fds, NULL, NULL, &timeout) > 0)
+		return ioctl(0, FIONREAD, &n) == 0 && n > 0;
+
+	return 0;
 }
 
 /* Private to libuEv, do not use directly! */
@@ -292,7 +297,6 @@ int uev_run(uev_ctx_t *ctx, int flags)
 				if (!has_data(w->fd)) {
 					w->active = 0;
 					LIST_REMOVE(w, link);
-					continue;
 				}
 
 				rerun++;