[2.4] Inconsistency in poll(2)
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 kernel.
Any suggestions which actions to take?
Michael
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 )
perror("poll");
else
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;
}Signature · 2 lines
Linux@TekXpress http://www-users.rwth-aachen.de/Michael.Mueller4/tekxp/tekxp.html
Hi,
Quoted 3 lines · I wrote:
The kernel is 2.4.20 (debian 2.4.20-3-686). After a short look at the code for
sys_pollI am certain the problem is originated within the kernel.
I should have been more carefully about locating the source. After trying strace, I know the kernel is not the source of the problem:
poll([{fd=0, events=POLLIN}, {fd=110, events=POLLIN, revents=POLLNVAL}], 2, -1) = 1
sorry for bothering you. I am going to file a bug for the glibc instead now.
Michael
Signature · 2 lines
Linux@TekXpress http://www-users.rwth-aachen.de/Michael.Mueller4/tekxp/tekxp.html
Quoted 6 lines · [email protected] (Michael Mueller) writes:
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.
[snip .. ]
Quoted 1 line
Simple sample code demonstrating the problem:
When writing code, always compile with at least -Wall -W
Quoted 9 lines
#include <
stdio.h>
#include <sys/poll.h>struct pollfd fds[] = {
{ 0, POLLIN, 0 },
{ 110, POLLIN, 0}
};
Quoted 7 lines
int main(void)
{ int r = poll(fds, sizeof fds / sizeof fds[0], -1); if ( r < 0 ) perror("poll"); else printf("poll returned %d\n");
printf("poll returned %d\n", r);
Is probably what you want.
Quoted 6 lines
for ( r=0; r < sizeof fds / sizeof fds[0]; r++ )
printf("revent[%d]: %hd\n", r, fds[r].revents);
return 0;
}Signature · 3 lines
James Antill -- [email protected] Need an efficent and powerful string library for C? http://www.and.org/vstr/