From 18f6b22fe1eb4447b26fafd3bed1e6bb23c9adc2 Mon Sep 17 00:00:00 2001
From: =?utf8?q?P=C3=A1draig=20Brady?= <P@draigBrady.com>
Date: Fri, 16 Jun 2017 23:50:47 -0700
Subject: [PATCH] tail: only use inotify with regular files

* src/tail.c (any_non_regular): A new function to check passed files.
(main): Use the above to skip inotify if any non regular files passed
like /dev/tty or /dev/ttyUSB0 etc.
* tests/tail-2/inotify-only-regular.sh: A new test.
* tests/local.mk: Reference the new test.
* NEWS: Mention the bug fix.
Fixes http://bugs.gnu.org/21265 and http://bugs.gnu.org/27368
---
 NEWS                                 |  4 ++++
 src/tail.c                           | 17 +++++++++++++++++
 tests/local.mk                       |  1 +
 tests/tail-2/inotify-only-regular.sh | 32 ++++++++++++++++++++++++++++++++
 4 files changed, 54 insertions(+)
 create mode 100755 tests/tail-2/inotify-only-regular.sh

diff --git a/NEWS b/NEWS
index eb0271cf8..071be4bb4 100644
--- a/NEWS
+++ b/NEWS
@@ -36,6 +36,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   or ignored until future events on the monitored files.
   [bug introduced with inotify support added in coreutils-7.5]
 
+  tail -f /dev/tty is now supported by not using inotify when any
+  non regular files are specified, as inotify is ineffective with these.
+  [bug introduced with inotify support added in coreutils-7.5]
+
   uptime no longer outputs the AM/PM component of the current time,
   as that's inconsistent with the 24 hour time format used.
   [bug introduced in coreutils-7.0]
diff --git a/src/tail.c b/src/tail.c
index 2f9b981f0..b8be1d21d 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -1339,6 +1339,22 @@ any_symlinks (const struct File_spec *f, size_t n_files)
   return false;
 }
 
+/* Return true if any of the N_FILES files in F is not
+   a regular file.  This is used to avoid adding inotify
+   watches on a device file for example, which inotify
+   will accept, but not give any events for.  */
+
+static bool
+any_non_regular (const struct File_spec *f, size_t n_files)
+{
+  size_t i;
+
+  for (i = 0; i < n_files; i++)
+    if (0 <= f[i].fd && ! S_ISREG (f[i].mode))
+      return true;
+  return false;
+}
+
 /* Return true if any of the N_FILES files in F represents
    stdin and is tailable.  */
 
@@ -2457,6 +2473,7 @@ main (int argc, char **argv)
                                || any_remote_file (F, n_files)
                                || ! any_non_remote_file (F, n_files)
                                || any_symlinks (F, n_files)
+                               || any_non_regular (F, n_files)
                                || (!ok && follow_mode == Follow_descriptor)))
         disable_inotify = true;
 
diff --git a/tests/local.mk b/tests/local.mk
index fdf3edfb2..6112e88ed 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -177,6 +177,7 @@ all_tests =					\
   tests/tail-2/inotify-rotate.sh		\
   tests/tail-2/inotify-rotate-resources.sh	\
   tests/tail-2/inotify-dir-recreate.sh		\
+  tests/tail-2/inotify-only-regular.sh		\
   tests/chmod/no-x.sh				\
   tests/chgrp/basic.sh				\
   tests/rm/dangling-symlink.sh			\
diff --git a/tests/tail-2/inotify-only-regular.sh b/tests/tail-2/inotify-only-regular.sh
new file mode 100755
index 000000000..4d106fbb8
--- /dev/null
+++ b/tests/tail-2/inotify-only-regular.sh
@@ -0,0 +1,32 @@
+#!/bin/sh
+# ensure that tail -f only uses inotify for regular files
+
+# Copyright (C) 2017 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/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ tail
+
+grep '^#define HAVE_INOTIFY 1' "$CONFIG_HEADER" >/dev/null \
+  || skip_ 'inotify support required'
+
+require_strace_ 'inotify_add_watch'
+
+returns_ 124 timeout .1 strace -e inotify_add_watch -o strace.out \
+  tail -f /dev/null || fail=1
+
+grep 'inotify' strace.out && fail=1
+
+Exit $fail
-- 
2.11.4.GIT