"M. Tavasti" wrote:
>
> I found this problem first time in 2.2 kernels, when doing own device
> driver. Then it was not an issue for me, and I suspected it's my
> fault. Now, with 2.4 again I tried to solve problem, but I can't find
> my way out of this, and looks like there in-kernel drivers which have
> same symptoms.
>
> Here program where I get problems:
>
> int fd;
> fd_set rfds;
>
> fd = open("/dev/random", O_RDWR );
>
> while(1) {
> FD_ZERO(&rfds);
> FD_SET(fd,&rfds);
> FD_SET(fileno(stdin),&rfds);
> if( select(fd+1, &rfds, NULL, NULL, NULL ) > 0) {
> fprintf(stderr,"Select\n");
> fflush(stderr);
> if(FD_ISSET(fd,&rfds)) {
> .......
> } else if(FD_ISSET(fileno(stdin),&rfds) ) {
> ......
> }
> }
> }
>
> Select is working fine for device (in this example /dev/random) or
> stdin. But for both, not. When entering something to stdin, it's not
> sure select will return.
>
> I haven't tested is this problem present in all devices, but at least
> /dev/random is infected. And if problem lies only in some of the
> drivers, it would be nice to know which driver haves decent
> implementation of poll and get others updated.
I also saw what I believe is a problem with select, but I haven't had
time to poke around the kernel to try to understand it. In my case,
the problem is that when I have raw sockets reading ethernet frames,
select will not return immediately when there is a packet ready. When
it does return, due to timeout, or another FD in the set being ready
for action, the FD is set correctly though. My hack/kludge/work-around
was to sleep for a max of 5ms, but that is not a clean, or efficient
solution. Another person sent private email to me claiming that he
saw the same problem, so it's likely I'm not insane on this issue :)
So, I do think there may be problems with select, but I'm not sure if it
relates to your problem or not.
Ben
>
> I'm not subsribed on the list, so when replying this you may consider
> Cc:ing me.
>
> --
> M. Tavasti / tawz@nic.fi / +358-40-5078254
> -
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-- Ben Greear <greearb@candelatech.com> <Ben_Greear@excite.com> President of Candela Technologies Inc http://www.candelatech.com ScryMUD: http://scry.wanfear.com http://scry.wanfear.com/~greear - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Tue Jul 31 2001 - 21:00:22 EST