uml: DEBUG_SHIRQ fixes

DEBUG_SHIRQ generates spurious interrupts, triggering handlers such as
mconsole_interrupt() or line_interrupt().  They expect data to be available to
be read from their sockets/pipes, but in the case of spurious interrupts, the
host didn't actually send anything, so UML hangs in read() and friends.
Setting those fd's as O_NONBLOCK makes DEBUG_SHIRQ-enabled UML kernels boot
and run correctly.

Signed-off-by: Eduard-Gabriel Munteanu <maxdamage@aladin.ro>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: Eduard-Gabriel Munteanu

arch/um/drivers/chan_user.c

@@ -170,7 +170,13 @@ static int winch_tramp(int fd, struct tty_struct *tty, int *fd_out)
                 err = -EINVAL;
 		goto out_close;
 	}
-	return err ;
+
+	if (os_set_fd_block(*fd_out, 0)) {
+		printk("winch_tramp: failed to set thread_fd non-blocking.\n");
+		goto out_close;
+	}
+
+	return err;
 
  out_close:
 	os_close_file(fds[1]);

arch/um/drivers/mconsole_user.c

@@ -86,8 +86,9 @@ int mconsole_get_request(int fd, struct mc_request *req)
 	int len;
 
 	req->originlen = sizeof(req->origin);
-	req->len = recvfrom(fd, &req->request, sizeof(req->request), 0,
-			    (struct sockaddr *) req->origin, &req->originlen);
+	req->len = recvfrom(fd, &req->request, sizeof(req->request),
+			    MSG_DONTWAIT, (struct sockaddr *) req->origin,
+			    &req->originlen);
 	if (req->len < 0)
 		return 0;
 

arch/um/drivers/ubd_user.c

@@ -43,6 +43,12 @@ int start_io_thread(unsigned long sp, int *fd_out)
 	kernel_fd = fds[0];
 	*fd_out = fds[1];
 
+	err = os_set_fd_block(*fd_out, 0);
+	if (err) {
+		printk("start_io_thread - failed to set nonblocking I/O.\n");
+		goto out_close;
+	}
+
 	pid = clone(io_thread, (void *) sp, CLONE_FILES | CLONE_VM | SIGCHLD,
 		    NULL);
 	if(pid < 0){

arch/um/drivers/xterm.c

@@ -151,6 +151,13 @@ int xterm_open(int input, int output, int primary, void *d,
 		goto out;
 	}
 
+	err = os_set_fd_block(new, 0);
+	if (err) {
+		printk("xterm_open : failed to set xterm descriptor "
+		       "non-blocking, err = %d\n", -err);
+		goto out;
+	}
+
 	CATCH_EINTR(err = tcgetattr(new, &data->tt));
 	if(err){
 		new = err;