Re: tail aborts while following by name if using inotify

[Jim Meyering]

Rob Wortman wrote:
> I have noticed a behavioral quirk in versions of tail which use inotify.
> When following a file by name (using tail -F or tail --follow=name),
> tail will abort when a file returns after being renamed. I see that this
> bug was addressed in coreutils-8.1, but I still find the behavior in
> coreutils-8.2.

Here's a first step: add a test to exercise the losing code.
The final "cat out" isn't required, but I found it handy while
writing the test, so left it in.

>From b8148d816296ba8e6ea942c95603f6475ab68dc6 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Mon, 28 Dec 2009 15:42:10 +0100
Subject: [PATCH] tail: add a test to exercise abort-inducing flaw in tail -F

* tests/tail-2/inotify-hash-abuse: New file, derived from
report by Rob Wortman.
* tests/Makefile.am (TESTS): Add it.
---
 THANKS                          |    1 +
 tests/Makefile.am               |    1 +
 tests/tail-2/inotify-hash-abuse |   63 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+), 0 deletions(-)
 create mode 100755 tests/tail-2/inotify-hash-abuse

diff --git a/THANKS b/THANKS
index 064c234..3167e90 100644
--- a/THANKS
+++ b/THANKS
@@ -512,6 +512,7 @@ Richard Sharman                     address@hidden
 Rick Sladkey                        address@hidden
 Rik Faith                           address@hidden
 Risto Kankkunen                     address@hidden
+Rob Wortman                         address@hidden
 Robert H. de Vries                  address@hidden
 Robert Lindgren                     address@hidden
 Robert Millan                       address@hidden
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 93d4275..35ea8b2 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -80,6 +80,7 @@ TESTS =                                               \
   rm/ext3-perf                                 \
   rm/cycle                                     \
   cp/link-heap                                 \
+  tail-2/inotify-hash-abuse                    \
   tail-2/inotify-rotate                                \
   chmod/no-x                                   \
   chgrp/basic                                  \
diff --git a/tests/tail-2/inotify-hash-abuse b/tests/tail-2/inotify-hash-abuse
new file mode 100755
index 0000000..7517075
--- /dev/null
+++ b/tests/tail-2/inotify-hash-abuse
@@ -0,0 +1,63 @@
+#!/bin/sh
+# Exercise an abort-inducing flaw in inotify-enabled tail -F.
+
+# 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
+
+for i in $(seq 9); do touch $i; done || framework_failure
+
+tail -qF $(seq 9) > out 2>&1 & pid=$!
+
+# Wait until tail has started...
+echo x > 9
+while :; do grep '^x$' out >/dev/null 2>&1 && break; done
+
+mv 1 f || fail=1
+
+# Wait for this diagnostic:
+# tail: `1' has become inaccessible: No such file or directory
+while :; do grep 'inaccessible' out >/dev/null 2>&1 && break; done
+echo a > 1 || fail=1
+
+# Before the fix, the above creation of a moved-aside file
+# would have caused tail to abort.  In that case, appending to
+# a tailed file and waiting for that new line to appear in tail's
+# output would have been an infloop.
+if kill -0 $pid; then
+  # Wait for tail to detect the changes.
+  echo y >> 8
+  while false ; do
+    grep '^y$' out >/dev/null 2>&1 && break
+  done
+fi
+
+wait $pid
+st=$?
+
+case $st in
+  129) ;;
+  *) echo tail died via unexpected signal: $st; fail=1;;
+esac
+
+cat out
+
+Exit $fail
--
1.6.6.301.g5794