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SubjectRe: [PATCH] /dev/epoll update ...

On 21-Sep-2001 Ton Hospel wrote:
> In article <XFMail.20010919151147.davidel@xmailserver.org>,
> Davide Libenzi <davidel@xmailserver.org> writes:
>> On 19-Sep-2001 Christopher K. St. John wrote:
>>> Davide Libenzi wrote:
>> Again :
>>
>> 1) select()/poll();
>> 2) recv()/send();
>>
>> vs :
>>
>> 1) if (recv()/send() == FAIL)
>> 2) ioctl(EP_POLL);
>>
>
> mm, I don't really get the second one. What if the scenario is:
> In the place you are in your program, you now decide that a
> read is in order. You try read, nothing there yet,
> the syscall returns, the data event happens and THEN you go into
> the ioctl ?
>
> Possibilities seem:
> 1) You hang, having missed the only event that will happen
> 2) Just having data triggers the ioctl (maybe only the first time),
> why not leaving out the initial read then and just do it afterwards
> like select ?
> 3) It generates a fake event the first time you notify interest, but then
> the startup case leads to doing the read uselessly twice.
>
> Or is there a fourth way I'm missing this really works ?

That was a simplified function :

while (recv()/send() == FAIL)
ioctl(EP_POLL);

this is the right code.
If an event happens between the recv() and the ioctl() this is cached by the
driver and it'll be returned from ioctl().




- Davide

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