[PATCH] tail -f: handle "-"/stdin once again

[Jim Meyering]

Here's the full patch:

>From b65cdea4dc1ec03be8bbc91cea261860373c8554 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Mon, 7 Sep 2009 08:37:08 +0200
Subject: [PATCH] tail -f: handle "-"/stdin once again

* src/tail.c (main) [HAVE_INOTIFY]: When stdin (i.e., "-", or no args,
but not /dev/stdin) is specified on the command line, don't use inotify.
Reported by Bill Brelsford in <http://bugs.debian.org/545422>.
* tests/tail-2/follow-stdin: New file.  Test for this.
* tests/Makefile.am (TESTS): Add the test.
* NEWS (Bug fixes): Mention it.
This bug was introduced in coreutils-7.5 via commit ae494d4b,
2009-06-02, "tail: use inotify if it is available".
---
 NEWS                      |    9 +++++++++
 THANKS                    |    1 +
 src/tail.c                |   14 +++++++++++++-
 tests/Makefile.am         |    1 +
 tests/tail-2/follow-stdin |   41 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 65 insertions(+), 1 deletions(-)
 create mode 100755 tests/tail-2/follow-stdin

diff --git a/NEWS b/NEWS
index b02d2da..5c7fb82 100644
--- a/NEWS
+++ b/NEWS
@@ -31,6 +31,15 @@ GNU coreutils NEWS                                    -*- 
outline -*-
   Before, this would print nothing and wait: stdbuf -o 4K tail -f /etc/passwd
   Note that this bug affects tail -f only when its standard output is buffered,
   which is relatively unusual.
+  [bug introduced in coreutils-7.5]
+
+  tail -f once again works with standard input.  inotify-enabled tail -f
+  would fail when operating on a nameless stdin.  I.e., tail -f < /etc/passwd
+  would say "tail: cannot watch `-': No such file or directory", yet the
+  relatively baroque tail -f /dev/stdin < /etc/passwd would work.  Now, the
+  offending usage causes tail to revert to its conventional sleep-based
+  (i.e., not inotify-based) implementation.
+  [bug introduced in coreutils-7.5]

 ** New features

diff --git a/THANKS b/THANKS
index 0c5bb40..2410866 100644
--- a/THANKS
+++ b/THANKS
@@ -78,6 +78,7 @@ Bernhard Rosenkraenzer              address@hidden
 Bernhard Voelker                    address@hidden
 Bert Deknuydt                       address@hidden
 Bert Wesarg                         address@hidden
+Bill Brelsford                      address@hidden
 Bill Peters                         address@hidden
 Bjorn Helgaas                       address@hidden
 Bob McCracken                       address@hidden
diff --git a/src/tail.c b/src/tail.c
index e3b9529..c53df9e 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -1982,7 +1982,19 @@ main (int argc, char **argv)
   if (forever)
     {
 #if HAVE_INOTIFY
-      if (!disable_inotify)
+      /* If the user specifies stdin via a command line argument of "-",
+         or implicitly by providing no arguments, we won't use inotify.
+         Technically, on systems with a working /dev/stdin, we *could*,
+         but would it be worth it?  Verifying that it's a real device
+         and hooked up to stdin is not trivial, while reverting to
+         non-inotify-based tail_forever is easy and portable.  */
+      bool stdin_cmdline_arg = false;
+
+      for (i = 0; i < n_files; i++)
+        if (STREQ (file[i], "-"))
+          stdin_cmdline_arg = true;
+
+      if (!disable_inotify && !stdin_cmdline_arg)
         {
           int wd = inotify_init ();
           if (wd < 0)
diff --git a/tests/Makefile.am b/tests/Makefile.am
index d83d41b..6b3c2b1 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -428,6 +428,7 @@ TESTS =                                             \
   tail-2/assert-2                              \
   tail-2/big-4gb                               \
   tail-2/flush-initial                         \
+  tail-2/follow-stdin                          \
   tail-2/proc-ksyms                            \
   tail-2/start-middle                          \
   touch/dangling-symlink                       \
diff --git a/tests/tail-2/follow-stdin b/tests/tail-2/follow-stdin
new file mode 100755
index 0000000..46e7ce8
--- /dev/null
+++ b/tests/tail-2/follow-stdin
@@ -0,0 +1,41 @@
+#!/bin/sh
+# tail -f - would fail with the initial inotify implementation
+
+# 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
+
+echo line > exp || framework_failure
+echo line > in || framework_failure
+
+fail=0
+timeout 1 tail -f < in > out 2> err
+
+# tail from coreutils-7.5 would fail
+test $? = 124 || fail=1
+
+# Ensure there was no error output.
+test -s err && fail=1
+
+# Ensure there was
+compare out exp || fail=1
+
+Exit $fail
--
1.6.4.2.419.gab238