openssh unix dev - Jan 2022 - OS X poll breakage (Was: Please help test recent changes)

On Tue, 11 Jan 2022, Demi Marie Obenour wrote:
> > Wow, it looks like Darwin's poll(2) is completely broken for
> > character- special devices (at least). E.g. the attached program
> > spins shows similar behaviour when run on /dev/null - it spins,
> > returning revents=POLLNVAL.
>
> Is using kqueue(2) an option? That?s faster, and it doesn?t have the
> problem with large file descriptors that poll(2) has.
No, because it's not cross-platform and I don't want to have to maintain
multiple mainloops (believe me, one is more than enough). It would have
been really nice if the OSS Unix-like operating systems has standardised
on one event notification; kqueue and epoll are both fine.

Also, it seems like the OS X kqueue(2) implementation suffers from the
same bug anyway. I suspect that this is the root cause, and that their
poll(2) is built on top of kqueue(2).

-d

epoll doesn't (or didn't) work with /dev/null either in any case.

Only select works on everything on macOS and only poll or select on Linux.



On Tue, 11 Jan 2022, 22:46 Damien Miller, <djm at mindrot.org> wrote:
> On Tue, 11 Jan 2022, Demi Marie Obenour wrote:
>
> > > Wow, it looks like Darwin's poll(2) is completely broken for
> > > character- special devices (at least). E.g. the attached program
> > > spins shows similar behaviour when run on /dev/null - it spins,
> > > returning revents=POLLNVAL.
> >
> > Is using kqueue(2) an option? That?s faster, and it doesn?t have the
> > problem with large file descriptors that poll(2) has.
>
> No, because it's not cross-platform and I don't want to have to
maintain
> multiple mainloops (believe me, one is more than enough). It would have
> been really nice if the OSS Unix-like operating systems has standardised
> on one event notification; kqueue and epoll are both fine.
>
> Also, it seems like the OS X kqueue(2) implementation suffers from the
> same bug anyway. I suspect that this is the root cause, and that their
> poll(2) is built on top of kqueue(2).
>
> -d
> _______________________________________________
> openssh-unix-dev mailing list
> openssh-unix-dev at mindrot.org
> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
>

On 1/11/22 17:42, Damien Miller wrote:
> On Tue, 11 Jan 2022, Demi Marie Obenour wrote:
> 
>>> Wow, it looks like Darwin's poll(2) is completely broken for
>>> character- special devices (at least). E.g. the attached program
>>> spins shows similar behaviour when run on /dev/null - it spins,
>>> returning revents=POLLNVAL.
>>
>> Is using kqueue(2) an option? That?s faster, and it doesn?t have the
>> problem with large file descriptors that poll(2) has.
> 
> No, because it's not cross-platform and I don't want to have to
maintain
> multiple mainloops (believe me, one is more than enough). It would have
> been really nice if the OSS Unix-like operating systems has standardised
> on one event notification; kqueue and epoll are both fine.
> 
> Also, it seems like the OS X kqueue(2) implementation suffers from the
> same bug anyway. I suspect that this is the root cause, and that their
> poll(2) is built on top of kqueue(2).
What about filtering out file descriptors belonging to /dev files?

-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
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