Ulrich Drepper wrote: > Jim Meyering wrote: >> Thanks for the report!
Ulrich and Ren reported that the command, echo foobar | tail -c3 -f would block indefinitely, while POSIX says that it must not. Here's how I expect to fix this. Maybe I'm splitting hairs, but rather than call this a bug in NEWS, (it's more like GIGO) I've put it in a new "POSIX conformance" category. This seems small and safe enough that I'm leaning toward including it in coreutils-7.6, but I'll wait for a second opinion and/or review. >From d4d7daeb391faafda795dff87212bbfe9611d26c Mon Sep 17 00:00:00 2001 From: Jim Meyering <meyer...@redhat.com> Date: Mon, 7 Sep 2009 22:10:10 +0200 Subject: [PATCH 1/2] tail: ignore -f for piped-stdin, as POSIX requires * src/tail.c (main): Tailing a pipe "forever" is not useful, and POSIX specifies that tail ignore the -f when there is no file argument and stdin is a FIFO or pipe. So we do that. In addition, GNU tail excludes "-" arguments from the list of files to tail forever, when the associated file descriptor is connected to a FIFO or pipe. Before this change, ":|tail -f" would hang. Reported by Ren Yang and Ulrich Drepper. * tests/tail-2/pipe-f: Test for this. * tests/tail-2/pipe-f2: Ensure tail doesn't exit early for a fifo. * tests/Makefile.am (TESTS): Add these tests. * NEWS (POSIX conformance): Mention it. --- NEWS | 6 ++++++ THANKS | 1 + src/tail.c | 16 +++++++++++++++- tests/Makefile.am | 2 ++ tests/tail-2/pipe-f | 32 ++++++++++++++++++++++++++++++++ tests/tail-2/pipe-f2 | 37 +++++++++++++++++++++++++++++++++++++ 6 files changed, 93 insertions(+), 1 deletions(-) create mode 100755 tests/tail-2/pipe-f create mode 100755 tests/tail-2/pipe-f2 diff --git a/NEWS b/NEWS index a5a6094..9efe5fc 100644 --- a/NEWS +++ b/NEWS @@ -46,6 +46,12 @@ GNU coreutils NEWS -*- outline -*- cp --reflink accepts a new "auto" parameter which falls back to a standard copy if creating a copy-on-write clone is not possible. +** POSIX conformance + + tail -f now ignores "-" when stdin is a pipe or FIFO, per POSIX. + Now, : | tail -f terminates immediately. Before, it'd block indefinitely. + [the old behavior dates back to the original implementation] + * Noteworthy changes in release 7.5 (2009-08-20) [stable] diff --git a/THANKS b/THANKS index 2410866..c6655eb 100644 --- a/THANKS +++ b/THANKS @@ -490,6 +490,7 @@ Ralph Loader loa...@maths.ox.ac.uk Raul Miller m...@magenta.com Raúl Núñez de Arenas Coronado r...@pleyades.net Reuben Thomas r...@sc3d.org +Ren Yang ry...@redhat.com Richard A Downing richard.down...@bcs.org.uk Richard Braakman d...@xs4all.nl Richard Dawe r...@phekda.freeserve.co.uk diff --git a/src/tail.c b/src/tail.c index 9288007..d75d9b3 100644 --- a/src/tail.c +++ b/src/tail.c @@ -1979,7 +1979,21 @@ main (int argc, char **argv) for (i = 0; i < n_files; i++) ok &= tail_file (&F[i], n_units); - if (forever) + /* When there is no FILE operand and stdin is a pipe or FIFO + POSIX requires that tail ignore the -f option. + Since we allow multiple FILE operands, we extend that to say: + ignore any "-" operand that corresponds to a pipe or FIFO. */ + size_t n_viable = 0; + for (i = 0; i < n_files; i++) + { + if (STREQ (F[i].name, "-") && !F[i].ignore + && 0 <= F[i].fd && S_ISFIFO (F[i].mode)) + F[i].ignore = true; + else + ++n_viable; + } + + if (forever && n_viable) { #if HAVE_INOTIFY /* If the user specifies stdin via a command line argument of "-", diff --git a/tests/Makefile.am b/tests/Makefile.am index 6b3c2b1..42a12cf 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -429,6 +429,8 @@ TESTS = \ tail-2/big-4gb \ tail-2/flush-initial \ tail-2/follow-stdin \ + tail-2/pipe-f \ + tail-2/pipe-f2 \ tail-2/proc-ksyms \ tail-2/start-middle \ touch/dangling-symlink \ diff --git a/tests/tail-2/pipe-f b/tests/tail-2/pipe-f new file mode 100755 index 0000000..b9f6ae3 --- /dev/null +++ b/tests/tail-2/pipe-f @@ -0,0 +1,32 @@ +#!/bin/sh +# ensure that :|tail -f doesn't hang, per POSIX + +# Copyright (C) 2009 Free Software Foundation, Inc. + +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation, either version 3 of the License, or +# (at your option) any later version. + +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. + +# You should have received a copy of the GNU General Public License +# along with this program. If not, see <http://www.gnu.org/licenses/>. + +if test "$VERBOSE" = yes; then + set -x + tail --version +fi + +. $srcdir/test-lib.sh + +fail=0 +echo foo | timeout 2 tail -f -c3 > out || fail=1 +echo oo > exp || fail=1 + +compare out exp || fail=1 + +Exit $fail diff --git a/tests/tail-2/pipe-f2 b/tests/tail-2/pipe-f2 new file mode 100755 index 0000000..406ebcc --- /dev/null +++ b/tests/tail-2/pipe-f2 @@ -0,0 +1,37 @@ +#!/bin/sh +# Ensure that "tail -f fifo" tails indefinitely. + +# Copyright (C) 2009 Free Software Foundation, Inc. + +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation, either version 3 of the License, or +# (at your option) any later version. + +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. + +# You should have received a copy of the GNU General Public License +# along with this program. If not, see <http://www.gnu.org/licenses/>. + +if test "$VERBOSE" = yes; then + set -x + tail --version +fi + +. $srcdir/test-lib.sh + +mkfifo_or_skip_ fifo + +echo 1 > fifo & +echo 1 > exp || framework_failure + +fail=0 +timeout 1 tail -f fifo > out +test $? = 124 || fail=1 + +compare out exp || fail=1 + +Exit $fail -- 1.6.4.2.419.gab238 >From aed1bee7a862c613e243050a0be14493ea6fedc4 Mon Sep 17 00:00:00 2001 From: Jim Meyering <meyer...@redhat.com> Date: Mon, 7 Sep 2009 22:36:05 +0200 Subject: [PATCH 2/2] tail: syntax-only: use "false", rather than equivalent, 0 * src/tail.c (record_open_fd): Initialize "->ignore" to false, not 0. --- src/tail.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/src/tail.c b/src/tail.c index d75d9b3..63874bb 100644 --- a/src/tail.c +++ b/src/tail.c @@ -358,7 +358,7 @@ record_open_fd (struct File_spec *f, int fd, f->mode = st->st_mode; f->blocking = blocking; f->n_unchanged_stats = 0; - f->ignore = 0; + f->ignore = false; } /* Close the file with descriptor FD and name FILENAME. */ -- 1.6.4.2.419.gab238