"H. Peter Anvin" <hpa@xxxxxxxxx> 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
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