[2.4] Inconsistency in poll(2)

From: Michael Mueller (malware@t-online.de)
Date: Wed Jul 16 2003 - 05:35:55 EST

Hi readers of linux-kernel and glibc maintainers,

while hacking on a network application I found following oddity:

poll(pds,nfds,timeout) called with one of the file descriptors listed in
pds being invalid always does return nfds.

Output of appended sample code:
poll returned 2
revent[0]: 0
revent[1]: 32

According to IEEE Std 1003.1, 2003 Edition, the return value should have
been 1 in the above sample.

The kernel is 2.4.20 (debian 2.4.20-3-686). After a short look at the
code for sys_poll I am certain the problem is originated within the

Any suggestions which actions to take?


Simple sample code demonstrating the problem:

#include <stdio.h>
#include <sys/poll.h>

struct pollfd fds[] = {
 { 0, POLLIN, 0 },
 { 110, POLLIN, 0}

int main(void)
        int r = poll(fds, sizeof fds / sizeof fds[0], -1);
        if ( r < 0 )
                printf("poll returned %d\n");

        for ( r=0; r < sizeof fds / sizeof fds[0]; r++ )
                printf("revent[%d]: %hd\n", r, fds[r].revents);

        return 0;

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