From: "M. Tavasti" <tawz@nic.fi>
To: linux-kernel@vger.kernel.org
Subject: Select with device and stdin not working
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Date: 25 Jul 2001 15:17:14 +0300
Message-ID: <m266chnqyd.fsf@akvavitix.vuovasti.com>
Lines: 44
Sender: linux-kernel-owner@vger.kernel.org
Original-Recipient: rfc822;linux-kernel-outgoing


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'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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