Re: [PATCH v5 4/5] docs: counter: Document character device interface

[David Lechner]

On 10/8/20 7:28 AM, William Breathitt Gray wrote:
> On Thu, Oct 08, 2020 at 10:09:09AM +0200, Pavel Machek wrote:
> > Hi!
> >
> > > +        int main(void)
> > > +        {
> > > +                struct pollfd pfd = { .events = POLLIN };
> > > +                struct counter_event event_data[2];
> > > +
> > > +                pfd.fd = open("/dev/counter0", O_RDWR);
> > > +
> > > +                ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches);
> > > +                ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches + 1);
> > > +                ioctl(pfd.fd, COUNTER_LOAD_WATCHES_IOCTL);
> > > +
> > > +                for (;;) {
> > > +                        poll(&pfd, 1, -1);
> >
> > Why do poll, when you are doing blocking read?
> >
> > > +                        read(pfd.fd, event_data,  sizeof(event_data));
> >
> > Does your new chrdev always guarantee returning complete buffer?
> >
> > If so, should it behave like that?
> >
> > Best regards,
> > 									Pavel
> > --
> > (english) http://www.livejournal.com/~pavelmachek
> > (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
>
> I suppose you're right: a poll() should be redundant now with this
> version of the character device implementation because buffers will
> always return complete; so a blocking read() should achieve the same
> behavior that a poll() with read() would.
>
> I'll give some more time for additional feedback to come in for this
> version of the patchset, and then likely remove support for poll() in
> the v6 submission.
>
> William Breathitt Gray

I hope that you mean that you will just remove it from the example
and not from the chardev. Otherwise it won't be possible to
integrate this with an event loop.