Add fix for output being O_NONBLOCK

This tries to remove the O_NONBLOCK flag from an output FD if the output seems
to be setup this way.

Signed-off-by: Tyrolyean <tyrolyean@tyrolyean.net>

shadermeh.c

@@ -5,6 +5,7 @@
  * Copyright (C) 2022 David Oberhollenzer <goliath@infraroot.at>
  */
 #include "shadermeh.h"
+#include <fcntl.h>
 
 static GLfloat vertex_buffer[] = {
 	-1.0f, -1.0f, 0.0f,	/* lower left corner */
@@ -51,10 +52,23 @@ static int write_retry(int fd, const void *buffer, size_t size)
 		int ret = write(fd, buffer, size);
 
 		if (ret < 0) {
-			if (errno == EINTR)
-				continue;
-			perror("write");
-			return -1;
+			if (errno == EINTR){
+                                continue;
+                        }else if(errno == EAGAIN){
+                                perror("Output pipe probably has O_NONBLOCK "
+                                        "set! Removing setting");
+                                ret = fcntl(STDOUT_FILENO, F_SETFL,
+                                        fcntl(STDOUT_FILENO,F_GETFL)
+                                        &(~O_NONBLOCK));
+				if(ret == -1){
+					perror("Failed to set STDOUT blocking");
+					return -1;
+				}
+                                continue;
+                        }else{
+                                perror("write");
+                        }
+                        return -1;
 		}
 
 		if (ret == 0)