[Twisted-Python] linux kernel 2.6.11-rc broke twisted process pipes

[Andrea Arcangeli]

On Tue, Mar 01, 2005 at 01:37:23AM +0100, Andrea Arcangeli wrote:
> I'm going to update a semi-productive system running twisted servers
> using processes too, with the new pipe_poll code too to see what happens
> (that's the good thing of not being fully productive yet, so I can
> experiment a bit more ;).

System is up and running fine with this patch against 2.6.8 that should
apply to most l-k out there, matching latest 2.6.11. This will bring
linux in sync with the twisted expectations of "r && w" meaning 'reader
disconnected' with select, it'll change the behaviour of poll not to
return POLLIN set unconditionally, and more specifically it'll never
return POLLIN for a WRONLY fd, and it'll never return POLLOUT for a
RDONLY fd.

--- x/fs/pipe.c.~1~	2004-08-25 02:47:51.000000000 +0200
+++ x/fs/pipe.c	2005-03-01 02:10:50.000000000 +0100
@@ -300,14 +300,18 @@ pipe_poll(struct file *filp, poll_table 
 
 	poll_wait(filp, PIPE_WAIT(*inode), wait);
 
-	/* Reading only -- no need for acquiring the semaphore.  */
-	mask = POLLIN | POLLRDNORM;
-	if (PIPE_EMPTY(*inode))
-		mask = POLLOUT | POLLWRNORM;
-	if (!PIPE_WRITERS(*inode) && filp->f_version != PIPE_WCOUNTER(*inode))
-		mask |= POLLHUP;
-	if (!PIPE_READERS(*inode))
-		mask |= POLLERR;
+	mask = 0;
+	if (filp->f_mode & FMODE_READ) {
+		mask |= PIPE_LEN(*inode) ? POLLIN | POLLRDNORM : 0;
+		if (!PIPE_WRITERS(*inode) && filp->f_version != PIPE_WCOUNTER(*inode))
+			mask |= POLLHUP;
+	}
+
+	if (filp->f_mode & FMODE_WRITE) {
+		mask |= PIPE_EMPTY(*inode) ? POLLOUT | POLLWRNORM : 0;
+		if (!PIPE_READERS(*inode))
+			mask |= POLLERR;
+	}
 
 	return mask;
 }