Date: Mon, 5 Aug 2002 15:23:57 +0000 (UTC) From: naddy@mips.inka.de (Christian Weisgerber) To: freebsd-current@freebsd.org Subject: devfs, fdescfs: /dev/fd problems Message-ID: <aim5ad$1tpa$1@kemoauc.mips.inka.de>
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The starting point is the observation that on -CURRENT with devfs
bash's process substitution doesn't work (this has been true for
months):
$ cat <(head /etc/rc)
cat: /dev/fd/63: No such file or directory
If you replace cat with a little program that just sleeps
$ ./s <( : )
62807
you can verify that the file descriptor is correctly associated
with a pipe:
$ fstat -p 62807
naddy s 62807 root / 26878976 ?--------- 1196525 r
naddy s 62807 wd /home 27309056 ?--S------ 2769389 r
naddy s 62807 text /home 27309056 ?--------- 98797 r
naddy s 62807 0 /dev 101 crw--w---- #C:255:0x-65281 rw
naddy s 62807 1 /dev 101 crw--w---- #C:255:0x-65281 rw
naddy s 62807 2 /dev 101 crw--w---- #C:255:0x-65281 rw
naddy s 62807 63* pipe fffffe0002b4d188 <-> 0 0 rw
Now let's try a program that lists the directory entries under
/dev/fd:
$ ./t <( : )
0
1
2
No entry 63. But there is something else amiss. readdir() is
reading from a file descriptor too, and that one doesn't show up
either.
Mounting fdescfs on /dev/fd improves things. bash's process
substitution works:
$ cat <(head /etc/rc)
#!/bin/sh
#
# Copyright (c) 2000 The FreeBSD Project
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
File descriptor assignment is still the same:
$ echo <( : )
/dev/fd/63
$ ./s <( : )
62853
$ fstat -p 62853
naddy s 62853 root / 26878976 ?--------- 1196525 r
naddy s 62853 wd /home 27309056 ?--S------ 2769389 r
naddy s 62853 text /home 27309056 ?--------- 98797 r
naddy s 62853 0 /dev 101 crw--w---- #C:255:0x-65281 rw
naddy s 62853 1 /dev 101 crw--w---- #C:255:0x-65281 rw
naddy s 62853 2 /dev 101 crw--w---- #C:255:0x-65281 rw
naddy s 62853 63* pipe fffffe0002b4c528 <-> 0 0 rw
Listing the entries under /dev/fd gives something of a surprise:
$ ./t <( : )
0
1
2
3
The descriptor used by readdir() is there, but the pipe on 63 is
still missing, although open()ing it obviously works.
Altogether I get the impression that /dev/fd doesn't quite work as
expected, for both plain devfs as well as for fdescfs.
---- s.c -------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(void)
{
int p = getpid();
printf("%d\n", p);
sleep(3600);
exit(0);
}
---- t.c -------------------------------------------------------
#include <sys/types.h>
#include <dirent.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[])
{
DIR *dirp;
struct dirent *dp;
if ((dirp = opendir("/dev/fd")) == NULL)
err(1, NULL);
while ((dp = readdir(dirp)) != NULL)
if (strcmp(".", dp->d_name) && strcmp("..", dp->d_name))
printf("%s\n", dp->d_name);
closedir(dirp);
exit(0);
}
--
Christian "naddy" Weisgerber naddy@mips.inka.de
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