Subject: bug#8544: tail bug - starting in 7.5 "tail --follow=name" behaves like "tail --follow=name --retry"

From: Jim Meyering <[email-masked]>
Date: Sun, 24 Apr 2011 23:22:46 +0200

Tim Underwood wrote:
> Going from Ubuntu 10.04 (coreutils 7.4) to Ubuntu 10.10 (coreutils 8.5) I
> noticed that "tail --follow=name" started behaving like "tail --follow=name
> --retry".  It looks like the issue started in 7.5 and still exists in 8.9.
>
> To reproduce:
>
> tail --follow=name this_file_does_not_exist
>
> The expected behavior is:
>
> $ ./coreutils-7.4/src/tail --follow=name this_file_does_not_exist
> ./coreutils-7.4/src/tail: cannot open `this_file_does_not_exist' for
> reading: No such file or directory
> ./coreutils-7.4/src/tail: no files remaining
>
> The wrong behavior is:
>
> $ ./coreutils-7.5/src/tail --follow=name this_file_does_not_exist
> ./coreutils-7.5/src/tail: cannot open `this_file_does_not_exist' for
> reading: No such file or directory
> <tail waits forever for this_file_does_not_exist to become available which
> is what --retry is for>
>
> Here's the wrong behavior on 8.9:
>
> $ ./coreutils-8.9/src/tail --follow=name this_file_does_not_exist
> ./coreutils-8.9/src/tail: cannot open `this_file_does_not_exist' for
> reading: No such file or directory
> <waits forever...>
>
> My specific use case is to tail a log file until it gets deleted at which
> point tail should exit allowing my script to continue.

Thanks again.
Here's the fix I expect to use:

>From 79a476abb35a69f409e2848019c8ebc24cc687cf Mon Sep 17 00:00:00 2001
From: Jim Meyering <[email-masked]>
Date: Sun, 24 Apr 2011 23:20:01 +0200
Subject: [PATCH] tail --follow=name no longer implies --retry

* src/tail.c (tail_forever_inotify): Just as without inotify,
tail --follow=name now terminates when the last tailed-by-name file
is unlinked or moved aside.  This bug was introduced on 2009-06-15
via commit ae494d4b, "tail: use inotify if it is available".
Reported by Tim Underwood in
http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/22286
* NEWS (Bug fixes): Mention this.
* tests/tail-2/follow-name: Test for this.
* tests/Makefile.am (TESTS): Add it.
---
 NEWS                     |    5 +++++
 THANKS.in                |    1 +
 src/tail.c               |   10 ++++++++++
 tests/Makefile.am        |    1 +
 tests/tail-2/follow-name |   32 ++++++++++++++++++++++++++++++++
 5 files changed, 49 insertions(+), 0 deletions(-)
 create mode 100755 tests/tail-2/follow-name

diff --git a/NEWS b/NEWS
index 7bc2ef3..3307e71 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,11 @@ GNU coreutils NEWS                                    -*- outline -*-

 * Noteworthy changes in release ?.? (????-??-??) [?]

+** Bug fixes
+
+  tail's --follow=name option no longer implies --retry on systems
+  with inotify support.  [bug introduced in coreutils-7.5]
+
 ** Changes in behavior

   cp's extent-based (FIEMAP) copying code is more reliable in the face
diff --git a/THANKS.in b/THANKS.in
index 342a52c..d1ca380 100644
--- a/THANKS.in
+++ b/THANKS.in
@@ -560,6 +560,7 @@ Tim J. Robbins                      [email-masked]
 Tim Mooney                          [email-masked]
 Tim Ryan                            [email-masked]
 Tim Smithers                        [email-masked]
+Tim Underwood                       [email-masked]
 Tim Waugh                           twaugh@redhat
 Toby Peterson                       [email-masked]
 Todd A. Jacobs                      [email-masked]
diff --git a/src/tail.c b/src/tail.c
index 88fbd10..e6d8164 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -1432,6 +1432,16 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
       struct File_spec *fspec;
       struct inotify_event *ev;

+      /* When following by name without --retry, and the last file has
+         been unlinked or renamed-away, diagnose it and return.  */
+      if (follow_mode == Follow_name
+          && ! reopen_inaccessible_files
+          && hash_get_n_entries (wd_to_name) == 0)
+        {
+          error (0, 0, _("no files remaining"));
+          return false;
+        }
+
       /* When watching a PID, ensure that a read from WD will not block
          indefinitely.  */
       if (pid)
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 685eb52..2f4a561 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -489,6 +489,7 @@ TESTS =						\
   tail-2/assert-2				\
   tail-2/big-4gb				\
   tail-2/flush-initial				\
+  tail-2/follow-name				\
   tail-2/follow-stdin				\
   tail-2/pipe-f					\
   tail-2/pipe-f2				\
diff --git a/tests/tail-2/follow-name b/tests/tail-2/follow-name
new file mode 100755
index 0000000..ef9434a
--- /dev/null
+++ b/tests/tail-2/follow-name
@@ -0,0 +1,32 @@
+#!/bin/sh
+# ensure that --follow=name does not imply --retry
+
+# Copyright (C) 2011 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=.}/init.sh"; path_prepend_ ../src
+print_ver_ tail
+
+cat <<\EOF > exp || framework_failure_
+tail: cannot open `no-such' for reading: No such file or directory
+tail: no files remaining
+EOF
+
+timeout 10 tail --follow=name no-such > out 2> err
+test $? = 1 || fail=1
+
+compare err exp || fail=1
+
+Exit $fail
--
1.7.5.rc3.316.gd1ff9