1 /* Test whether a file descriptor is a pipe.
3 Copyright (C) 2006 Free Software Foundation, Inc.
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 2, or (at your option)
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, write to the Free Software Foundation,
17 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
19 /* Written by Paul Eggert. */
27 #include <sys/types.h>
31 #include "stat-macros.h"
33 /* Whether pipes are FIFOs; -1 if not known. */
34 #ifndef HAVE_FIFO_PIPES
35 # define HAVE_FIFO_PIPES (-1)
38 /* The maximum link count for pipes; (nlink_t) -1 if not known. */
39 #ifndef PIPE_LINK_COUNT_MAX
40 # define PIPE_LINK_COUNT_MAX ((nlink_t) (-1))
43 /* Return 1 if FD is a pipe, 0 if not, -1 (setting errno) on error.
45 Test fairly strictly whether FD is a pipe. lseek and checking for
46 ESPIPE does not suffice, since many non-pipe files cause lseek to
47 fail with errno == ESPIPE. */
52 nlink_t pipe_link_count_max = PIPE_LINK_COUNT_MAX;
53 bool check_for_fifo = (HAVE_FIFO_PIPES == 1);
55 int fstat_result = fstat (fd, &st);
57 if (fstat_result != 0)
60 /* We want something that succeeds only for pipes, but on
61 POSIX-conforming hosts S_ISFIFO succeeds for both FIFOs and pipes
62 and we know of no portable, reliable way to distinguish them in
63 general. However, in practice pipes always have a link count <=
64 PIPE_LINK_COUNT_MAX (unless someone attaches them to the file
65 system name space using fattach, in which case they're not really
66 pipes any more), so test for that as well.
68 On Darwin 7.7, pipes are sockets, so check for those instead. */
70 if (! ((HAVE_FIFO_PIPES == 0 || HAVE_FIFO_PIPES == 1)
71 && PIPE_LINK_COUNT_MAX != (nlink_t) -1)
72 && (S_ISFIFO (st.st_mode) | S_ISSOCK (st.st_mode)))
75 int pipe_result = pipe (fd);
81 int fstat_pipe_result = fstat (fd[0], &pipe_st);
82 int fstat_pipe_errno = errno;
85 if (fstat_pipe_result != 0)
87 errno = fstat_pipe_errno;
88 return fstat_pipe_result;
90 check_for_fifo = (S_ISFIFO (pipe_st.st_mode) != 0);
91 pipe_link_count_max = pipe_st.st_nlink;
96 (st.st_nlink <= pipe_link_count_max
97 && (check_for_fifo ? S_ISFIFO (st.st_mode) : S_ISSOCK (st.st_mode)));