lkml.org 
[lkml]   [2012]   [Apr]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] nextfd(2)
Date
"H. Peter Anvin" <hpa@zytor.com> writes:

> On 04/06/2012 02:54 AM, Alexey Dobriyan wrote:
>>
>> Without proc knowledge about fdtable is gathered linearly and still unreliable.
>> With nextfd(2), even procful environments could lose several failure branches.
>> And they can keep old dumb fd++ or smart /proc/self/fd loops for a change.
>>
>
> Incidentally, if we were to create a system call for this -- which I so
> far see no reason for -- I would make it return a select-style bitmask
> of file descriptors in use, not a "next fd" which would require a system
> call per iteration.

It's already possible to do something a little like that with the
existing "poll" system call:

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

int
main(void)
{
enum { N_FDS = 1024 };
struct pollfd fds[N_FDS];
int error;
int i;
for (i = 0; i < N_FDS; i++)
{
fds[i].fd = i;
fds[i].events = 0;
}
error = poll(fds, N_FDS, 0);
if (error < 0)
perror("poll");
else
{
printf("valid fds:");
for (i = 0; i < N_FDS; i++)
if (!(fds[i].revents & POLLNVAL))
printf(" %d", fds[i].fd);
printf("\n");
}
return 0;
}
blp@blp:~/tmp(0)$ gcc tmp.c -Wall
blp@blp:~/tmp(0)$ ./a.out
valid fds: 0 1 2
blp@blp:~/tmp(0)$ ./a.out 5>/dev/null
valid fds: 0 1 2 5
blp@blp:~/tmp(0)$ ./a.out 5>/dev/null 3</dev/stdin
valid fds: 0 1 2 3 5
blp@blp:~/tmp(0)$

--
Ben Pfaff
http://benpfaff.org


\
 
 \ /
  Last update: 2012-04-07 23:55    [from the cache]
©2003-2011 Jasper Spaans