RE: Is psSocketPoll doing the right thing?

Dear Horiguchi-san,

My comment may be no longer needed, but I can +1 to your opinion.

> > On 2023/02/09 11:50, Kyotaro Horiguchi wrote:
> > > Hello.
> > > While looking a patch, I found that pqSocketPoll passes through the
> > > result from poll(2) to the caller and throws away revents. If I
> > > understand it correctly, poll() *doesn't* return -1 nor errno by the
> > > reason it has set POLLERR, POLLHUP, POLLNVAL, and POLLRDHUP for
> some
> > > of the target sockets, and returns 0 unless poll() itself failed to
> > > work.
> >
> > As far as I understand correctly, poll() returns >0 if "revents"
> > has either of those bits, not 0 nor -1.
>
> Right. as my understanding.
>
> If any of the sockets is in any of the states, pqSocketPoll returns a
> positive, which makes pqSocketCheck return 1. Finally
> pqRead/WriteReady return "ready" even though the connection socket is
> in an error state. Actually that behavior doesn't harm since the
> succeeding actual read/write will "properly" fail. However, once we
> use this function to simply check the socket is sound without doing an
> actual read/write, that behavior starts giving a harm by the false
> answer.

I checked man page of poll(3), and it said that POLLERR, POLLHUP, POLLNVAL is only
valid in revents. Moreover, poll() has is clarified that it returns natural number
if revent is larger than zero. So revent should be checked even if the returned
value > 0.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED