RTEMS5 and file descriptors

[Michael Davidsaver]

On 10/17/22 22:50, Chris Johns wrote:
> On 18/10/2022 4:42 pm, Sebastian Huber wrote:
>> On 18/10/2022 06:15, Chris Johns wrote:
>>> On 18/10/2022 2:22 pm, Michael Davidsaver wrote:
>>>> On 10/17/22 16:20, Chris Johns wrote:
>>>>> 2. Look at kqueue, it is a better interface for this type of blocking
>>>> Maybe not relevant in Miroslaw's application, but I've found
>>>> that the RTEMS kqueue implementation doesn't notify when a
>>>> TCP connection is closed by reset.  I think this is a lack
>>>> of NOTE_EOF *.
>>> Thanks. I cannot find a ticket for this? Do you know if one has been created?

Not by me.  I ran into this incidentally while testing some
new networking code using libevent, which helped me towards
finding:

https://www.mail-archive.com/freebsd-hackers@freebsd.org/msg43808.html

Which leads with a reasonably clear statement that kqueue
is/was not 100% functionally equivalent to select()/poll().
At that point I configured libevent to use poll() and
continued with my own troubleshooting.  Then unfortunately,
I forgot about it until I read this thread.

https://github.com/mdavidsaver/pvxs/blob/6ee82fac6533d6551b18aa489cb263adc1333018/src/evhelper.cpp#L171-L178

That freebsd thread is 19 years old, and I haven't spent the
time to investigate what happened since then.

libevent has:

> #ifdef NOTE_EOF
> 		/* Make it behave like select() and poll() */
> 		if (filter == EVFILT_READ)
> 			out->fflags = NOTE_EOF;
> #endif
https://github.com/libevent/libevent/blob/8f47d8de281b877450474734594fdc0a60ee35d1/kqueue.c#L193-L197


>> This looks like a general FreeBSD limitation.

This was my general assessment at the time.

  
> Is NOTE_EOF the same as EV_EOF? I noticed EV_EOF in the FreeBSD man page for kqueue.

I'm no expert on the kqueue mechanism, but I think not.

https://man.openbsd.org/kqueue.2

This openbsd manpage mentions both, although 'NOTE_EOF' is
only mentioned in passing, with no definition given.

Some searching leads me to think that EV_EOF is a "flag"
while NOTE_EOF is an "fflag" (filter flag).  I have not
investigated the precise distinction between the two.