tests: add a test for the `tail -f' race condition bug

If new data becomes available between the initial read and when tail
registers the inotify watch descriptors, ensure that it is read
before a new event happens on the file.
* tests/Makefile.am (TESTS): Add tail-2/inotify-race.
* tests/tail-2/inotify-race: New file.

2 files changed, 67 insertions, 0 deletions

diff --git a/tests/Makefile.am b/tests/Makefile.am
index 62583477b..ae17e9fe2 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -74,6 +74,7 @@ EXTRA_DIST += $(TESTS)
 
 TESTS =						\
   misc/help-version				\
+  tail-2/inotify-race			        \
   misc/invalid-opt				\
   rm/ext3-perf					\
   rm/cycle					\
diff --git a/tests/tail-2/inotify-race b/tests/tail-2/inotify-race
new file mode 100755
index 000000000..025272c02
--- /dev/null
+++ b/tests/tail-2/inotify-race
@@ -0,0 +1,66 @@
+#!/bin/sh
+# Ensure that tail does not ignore data that is appended to a tailed-forever
+# file between tail's initial read-to-EOF, and when the inotify watches
+# are established in tail_forever_inotify.  That data could be ignored
+# indefinitely if no *other* data is appended, but it would be printed as
+# soon as any additional appended data is detected.
+
+# 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
+
+touch file || framework_failure
+touch tail.out || framework_failure
+
+( gdb --version ) > gdb.out 2>&1
+case $(cat gdb.out) in
+    *'GNU gdb'*) ;;
+    *) skip_test_ "can't run gdb";;
+esac
+
+# See if gdb works:
+gdb -nx --batch-silent              \
+    --eval-command='break tail_forever_inotify'    \
+    --eval-command='run -f file'    \
+    --eval-command='quit'    \
+    tail < /dev/null > gdb.out 2>&1
+
+test -s gdb.out && skip_test_ "can't set breakpoints in tail"
+
+# Run "tail -f file", stopping to append a line just before
+# inotify initialization, and then continue.  Before the fix,
+# that just-appended line would never be output.
+timeout 10s gdb -nx --batch-silent    \
+    --eval-command='break tail_forever_inotify'    \
+    --eval-command='run -f file >> tail.out'    \
+    --eval-command="shell echo never-seen-with-tail-7.5 >> file" \
+    --eval-command='continue' \
+    --eval-command='quit'    \
+    tail < /dev/null &
+pid=$!
+
+tail --pid=$pid -f tail.out | (read; kill $pid)
+
+test -s tail.out || fail=1
+
+Exit $fail