Re: [Xenomai-help] rt_pipe does not support POLLHUP on the Linux side

[Wolfgang Grandegger <wg@domain.hid>]

Hi Gilles,

On 03/23/2012 02:14 PM, Gilles Chanteperdrix wrote:
> On 03/23/2012 10:59 AM, Gilles Chanteperdrix wrote:
>> On 03/23/2012 09:35 AM, Wolfgang Grandegger wrote:
>>> Hello,
>>>
>>> while playing with rt_pipe, I realized that a select()/poll() function
>>> does not unblock when the rt_pipe is deleted (via rt_pipe_delete) on the
>>> other end. I think this is because the poll callback does not support
>>> POLLHUP:
>>>
>>> http://www.rts.uni-hannover.de/xenomai/lxr/source/ksrc/nucleus/pipe.c#1024
>>>
>>> Is this by purpose? At least a blocking read() works as expected. It
>>> does unblock and return 0 in that case.
>>
>> rt_pipes are deprecated, we are not going to add new features to them
>> now. Please do not use them for new developments. We now have socket
>> based RTIPCs. See examples/rtdm/profiles/ipc.

Ah, I was not aware of that. This solution does also work for any skin
(and does not require to misuse the native skin any more).

> On the other hand, if you have a small patch to fix this, I will not
> hurt anyone to merge it.

OK. See patch below.

Wolfgang.


>From 49eeb2b8451a68d10a7f1768e2bf74dcdaf3e35e Mon Sep 17 00:00:00 2001
From: Wolfgang Grandegger <wg@domain.hid>
Date: Mon, 26 Mar 2012 09:21:51 +0200
Subject: [PATCH] nucleus: fix poll EOF issue with xnpipe/rt_pipe

So far, the EOF event is not handled in the Linux poll function of the
xnpipe/rt_pipe service when the pipe is closed (via rt_pipde_delete).
This patch fixes the issue by setting POLLUP in the Linux poll function
when the pipe is broken. The subsequent reads will then fail with errno
EPIPE.

Signed-off-by: Wolfgang Grandegger <wg@domain.hid>
---
 ksrc/nucleus/pipe.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/ksrc/nucleus/pipe.c b/ksrc/nucleus/pipe.c
index 1e6bcf2..1d5e39a 100644
--- a/ksrc/nucleus/pipe.c
+++ b/ksrc/nucleus/pipe.c
@@ -1033,6 +1033,8 @@ static unsigned xnpipe_poll(struct file *file, poll_table *pt)
 
 	if (testbits(state->status, XNPIPE_KERN_CONN))
 		w_mask |= (POLLOUT | POLLWRNORM);
+	else
+		r_mask |= POLLHUP;
 
 	if (!emptyq_p(&state->outq))
 		r_mask |= (POLLIN | POLLRDNORM);
-- 
1.7.7.6