On Mon, Feb 25, 2019 at 05:07:25PM +0100, Michael Kerrisk wrote:
> On Tue, 5 Feb 2019 at 20:08, Ricardo Biehl Pasquali wrote:
> > +.BR SO_SELECT_ERR_QUEUE " (since Linux 3.10)"
> > +.\" commit 7d4c04fc170087119727119074e72445f2bb192b
> > +.\" Author: Keller, Jacob E <jacob.e.keller@xxxxxxxxx>
> > +Masks
> > +.B POLLPRI
> > +with
> > +.B POLLERR
> > +event return.
>
> What does "Masks... with" mean? It's not clear to me.
Let me rewrite the sentence:
The flag SO_SELECT_ERR_QUEUE results in poll returning
(POLLERR | POLLPRI) whenever it would return POLLERR.
> Does "This was created when" mean "This flag was added when"?
Yes.
> > +.B POLLERR
> > +wake up depended on requesting
> > +.B POLLIN
> > +or
> > +.BR POLLPRI .
> > +After the commit 6e5d58fdc9bedd0255a8 ("skbuff: Fix not
> > +waking applications when errors are enqueued"), introduced
> > +in Linux 4.16,
> > +.B POLLERR
> > +wakes up normally.
> > +The option has no effect in wake up behavior, all it does
> > +is masking
> > +.B POLLPRI
> > +before poll returns.
>
> So, I'm not sure if I quite understand the text above. Do you mean
> that since Linux 4.16, SO_SELECT_ERR_QUEUE is no longere needed for
> its original purpose and that now its only effect is to "mask
> POLLPRI"? (And still, it's not clear to me what "masking POLLPRI"
> means.)
Ok, let me rewrite everything:
SO_SELECT_ERR_QUEUE makes poll adding POLLPRI when POLLERR
event is returned. It does not affect wake up.
Background: The flag was added when waking up on POLLERR
required requesting POLLIN or POLLPRI. After the commit
6e5d58fdc9bedd0255a8 ("skbuff: Fix not waking applications
when errors are enqueued"), introduced in Linux 4.16,
waking up on POLLERR does not require requesting other
events.
One more thing, the flag's effect seems to apply only for
some types of socket (perhaps only datagram ones?). Jacob?
<https://git.kernel.org/pub/scm/linux/kernel/git/davem/
net.git/diff/?h=7d4c04fc1700>.
The intention is to have a short and simple description that
explain it all.
pasquali
