Date: Sun, 16 Oct 2022 00:55:30 +0300 From: =?UTF-8?B?0K/RgNC+0YHQu9Cw0LIg0JzQsNGI0LrQvg==?= <yaroslaw.mashko@gmail.com> To: freebsd-questions@freebsd.org Subject: clarification on kqueue kernel event flags. Message-ID: <CAMVwyx%2BpagV6%2Bcp%2BMJCOz=HYvxDCCEVQBVkVYpi-%2BY9X80XOPg@mail.gmail.com>
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[-- Attachment #1 --]
Hello,
I got confused with EV_CLEAR flag. Some code follows.
kev.ident = 1;
kev.filter = EVFILT_TIMER;
kev.flags = EV_ADD | EV_DISPATCH;
kev.data = 4;
kev.fflags = NOTE_SECONDS;
l_reg_ev:
status = kevent(kq, &kev, 1, NULL, 0, NULL);
for(;;){
status = kevent(kq, NULL, 0, &kev, 1, NULL);
kev.flags = EV_ENABLE;
goto l_reg_ev;
}
This prints the series of:
id : 1
> flags : EV_DISPATCH EV_CLEAR
> filter : EVFILT_TIMER
> data : # times timeout has expired since last kevent call: 1
>
The "man kevent", the EV_CLEAR section says that:
> After the event is retrieved by the user, its state is reset.
>
What I expect is that after the first goto, the EV_DISPATCH flag gets
cleared. What does "the state" mean in the above?
More specifically, what exactly EV_CLEAR changes with any combination of
flags and filters?
P.S.
I did read a source code for "/sys/kern/kern_event.c". My brain fails to
understand it as a whole, so, please be easy on me.
--
Ярослав Машко
+380 50 56 75 347 <+380+50+56+75+347>
[-- Attachment #2 --]
<div dir="ltr"><div>Hello,</div><div><br></div><div>I got confused with EV_CLEAR flag. Some code follows.</div><div><br></div><div> kev.ident = 1;<br> kev.filter = EVFILT_TIMER;<br> kev.flags = EV_ADD | EV_DISPATCH;<br> kev.data = 4;<br> kev.fflags = NOTE_SECONDS;</div><div><br></div><div> l_reg_ev:</div><div> status = kevent(kq, &kev, 1, NULL, 0, NULL);</div><div><br></div><div> for(;;){</div><div> status = kevent(kq, NULL, 0, &kev, 1, NULL);</div><div> kev.flags = EV_ENABLE;</div><div> goto l_reg_ev;</div><div> }</div><div><br></div><div>This prints the series of:</div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div> id : 1<br> flags : EV_DISPATCH EV_CLEAR <br> filter : EVFILT_TIMER<br> data : # times timeout has expired since last kevent call: 1<br></div></blockquote><div> </div><div>The "man kevent", the EV_CLEAR section says that: <br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>After the event is retrieved by the user, its state is reset.</div></blockquote><div><br></div><div>What I expect is that after the first goto, the EV_DISPATCH flag gets cleared. What does "the state" mean in the above?</div><div>More specifically, what exactly EV_CLEAR changes with any combination of flags and filters?</div><div><br></div><div>P.S.<br></div><div>I did read a source code for "/sys/kern/kern_event.c". My brain fails to understand it as a whole, so, please be easy on me.<br></div><div><br>-- <br><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr">Ярослав Машко</div><div dir="ltr"><br><div><a href="tel:+380+50+56+75+347" target="_blank">+380 50 56 75 347</a></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>
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