RFC: poll change
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Quoted 9 lines · David S. Miller
From: Tim Hockin <[email protected]>
Date: Tue, 14 Aug 2001 16:53:43 -0700The standard says negative fd's are ignored. We get that right. What we are left with is an overly paranoid check against
max_fds. This check should go away. You should be able to pass in up to your rlimit fds, and let negative ones (holes or tails) be ignored.
Quoted 5 lines
I am saying there is no problem.
In both cases, for a properly written application we ignore the invalid fds. The behavior is identical both before and after your change, so there is no reason to make it.
But for an application that (imho) is poorly written but IS COMPLIANT, it fails.
This program is compliant, if your ulimit -n is maxxed out at 1048576.
I'm not saying it is good design, but it is compliant. The patch hurts nothing and makes poll() that little bit more friendly.
#include <stdio.h>
#include <sys/poll.h>
#include <errno.h>
#include <string.h>
int
main(void)
{
static struct pollfd ar[1024*1024];
int size = sizeof(ar)/sizeof(*ar);
int i;
for (i = 0; i < size; i++)
ar[i].fd = -1;
ar[1000000].fd = 0;
ar[1000000].events = POLLIN;
i = poll(ar, size, -1);
printf("return = %d (%s)\n", i, i?strerror(errno):"success");
return 0;
}Signature · 4 lines
Tim Hockin Systems Software Engineer Sun Microsystems, Cobalt Server Appliances [email protected]
From: Tim Hockin <[email protected]>
Date: Tue, 14 Aug 2001 17:09:00 -0700
But for an application that (imho) is poorly written but IS COMPLIANT, it fails.
This program is compliant, if your ulimit -n is maxxed out at 1048576.
This program is stupid.
Later,
David S. Miller
[email protected]
Quoted 2 lines · David S. Miller
invalid fds. The behavior is identical both before and after your change, so there is no reason to make it.
actually I can see a case where it makes difference: if you sends 1024 entries to poll with the last entry of the array polling for one of the allocated file descriptors (all previous 1023 entries are negative) and the last fd allocated is ID 255.
Andrea