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

[linux-kernel@ton.iguana.be (Ton Hospel)]

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 ?