tail: fix -f to follow changes after a rename

* src/tail.c (tail_forever_inotify): Only monitor write()s and
truncate()s to files in --follow=descriptor mode, thus avoiding
the bug where we removed the watch on renamed files.
Also adjust the inotify event processing code that is
now significant only in --follow=name mode.
* tests/tail-2/F-vs-rename.sh: Improve this existing test by running
in both polling and inotify modes.
* tests/tail-2/f-vs-rename.sh: A new test based on the existing one.
* tests/local.mk: Reference the new test.
* NEWS: Mention the bug.
Fixes http://bugs.gnu.org/19760

3 files changed, 100 insertions, 46 deletions

diff --git a/tests/local.mk b/tests/local.mk
index 56cba699a..1be31ad1d 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -171,6 +171,7 @@ all_tests =					\
   tests/tail-2/inotify-hash-abuse2.sh		\
   tests/tail-2/F-vs-missing.sh			\
   tests/tail-2/F-vs-rename.sh			\
+  tests/tail-2/f-vs-rename.sh			\
   tests/tail-2/inotify-rotate.sh		\
   tests/tail-2/inotify-rotate-resources.sh	\
   tests/chmod/no-x.sh				\
diff --git a/tests/tail-2/F-vs-rename.sh b/tests/tail-2/F-vs-rename.sh
index cb6a3ed8b..f95b71a6f 100755
--- a/tests/tail-2/F-vs-rename.sh
+++ b/tests/tail-2/F-vs-rename.sh
@@ -1,7 +1,7 @@
 #!/bin/sh
-# demonstrate that tail -F works when renaming the tailed files
-# Before coreutils-8.3, tail -F a b would stop tracking additions to b
-# after "mv a b".
+# Demonstrate that tail -F works when renaming the tailed files.
+# Between coreutils 7.5 and 8.2 inclusive, 'tail -F a b' would
+# stop tracking additions to b after 'mv a b'.
 
 # Copyright (C) 2009-2015 Free Software Foundation, Inc.
 
@@ -21,55 +21,57 @@
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
 print_ver_ tail
 
-touch a b || framework_failure_
-
-debug='---disable-inotify'
-debug=
-tail $debug -F -s.1 a b > out 2>&1 & pid=$!
-
 check_tail_output()
 {
   local delay="$1"
-  grep "$tail_re" out > /dev/null ||
+  grep "$tail_re" out ||
     { sleep $delay; return 1; }
 }
 
-# Wait up to 12.7s for tail to start
-echo x > a
-tail_re='^x$' retry_delay_ check_tail_output .1 7 || fail=1
-
-mv a b || fail=1
-
-# Wait 12.7s for this diagnostic:
-# tail: 'a' has become inaccessible: No such file or directory
-tail_re='inaccessible' retry_delay_ check_tail_output .1 7 || fail=1
-
-echo x > a
-# Wait up to 12.7s for this to appear in the output:
-# "tail: '...' has appeared;  following end of new file"
-tail_re='has appeared' retry_delay_ check_tail_output .1 7 ||
-  { echo "$0: a: unexpected delay?"; cat out; fail=1; }
-
-echo y >> b
-# Wait up to 12.7s for "y" to appear in the output:
-tail_f_vs_rename_2() {
-  local delay="$1"
-  tr '\n' @ < out | grep '@@==> b <==@y@$' > /dev/null ||
-    { sleep $delay; return 1; }
-}
-retry_delay_ tail_f_vs_rename_2 .1 7 ||
-  { echo "$0: b: unexpected delay?"; cat out; fail=1; }
-
-echo z >> a
-# Wait up to 12.7s for "z" to appear in the output:
-tail_f_vs_rename_3() {
-  local delay="$1"
-  tr '\n' @ < out | grep '@@==> a <==@z@$' > /dev/null ||
-    { sleep $delay; return 1; }
-}
-retry_delay_ tail_f_vs_rename_3 .1 7 ||
-  { echo "$0: a: unexpected delay?"; cat out; fail=1; }
+touch a b || framework_failure_
 
-kill -HUP $pid
+for mode in '' '---disable-inotify'; do
+  tail $mode -F -s.1 a b > out 2>&1 & pid=$!
+
+  # Wait up to 12.7s for tail to start.
+  echo x > a
+  tail_re='^x$' retry_delay_ check_tail_output .1 7 || fail=1
+
+  mv a b || fail=1
+
+  # Wait 12.7s for this diagnostic:
+  # tail: 'a' has become inaccessible: No such file or directory
+  tail_re='inaccessible' retry_delay_ check_tail_output .1 7 || fail=1
+
+  echo x > a
+  # Wait up to 12.7s for this to appear in the output:
+  # "tail: '...' has appeared;  following end of new file"
+  tail_re='has appeared' retry_delay_ check_tail_output .1 7 ||
+    { echo "$0: a: unexpected delay?"; cat out; fail=1; }
+
+  echo y >> b
+  # Wait up to 12.7s for "y" to appear in the output:
+  tail_f_vs_rename_2() {
+    local delay="$1"
+    tr '\n' @ < out | grep '@@==> b <==@y@$' > /dev/null ||
+      { sleep $delay; return 1; }
+  }
+  retry_delay_ tail_f_vs_rename_2 .1 7 ||
+    { echo "$0: b: unexpected delay?"; cat out; fail=1; }
+
+  echo z >> a
+  # Wait up to 12.7s for "z" to appear in the output:
+  tail_f_vs_rename_3() {
+    local delay="$1"
+    tr '\n' @ < out | grep '@@==> a <==@z@$' > /dev/null ||
+      { sleep $delay; return 1; }
+  }
+  retry_delay_ tail_f_vs_rename_3 .1 7 ||
+    { echo "$0: a: unexpected delay?"; cat out; fail=1; }
+
+  kill $pid
+
+  wait $pid
+done
 
 Exit $fail
diff --git a/tests/tail-2/f-vs-rename.sh b/tests/tail-2/f-vs-rename.sh
new file mode 100755
index 000000000..4bff41ce3
--- /dev/null
+++ b/tests/tail-2/f-vs-rename.sh
@@ -0,0 +1,51 @@
+#!/bin/sh
+# Demonstrate that tail -f works when renaming the tailed files.
+# Between coreutils 7.5 and 8.23 inclusive, 'tail -f a' would
+# stop tracking additions to b after 'mv a b'.
+
+# Copyright (C) 2015 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ tail
+
+check_tail_output()
+{
+  local delay="$1"
+  grep "$tail_re" out ||
+    { sleep $delay; return 1; }
+}
+
+touch a || framework_failure_
+
+for mode in '' '---disable-inotify'; do
+  tail $mode -f -s.1 a > out 2>&1 & pid=$!
+
+  # Wait up to 12.7s for tail to start.
+  echo x > a
+  tail_re='^x$' retry_delay_ check_tail_output .1 7 || fail=1
+
+  mv a b || fail=1
+
+  echo y >> b
+  # Wait up to 12.7s for "y" to appear in the output:
+  tail_re='^y$' retry_delay_ check_tail_output .1 7 || fail=1
+
+  kill $pid
+
+  wait $pid
+done
+
+Exit $fail