tail: -F now always processes initially untailable files

which was not the case when inotify was not available.

* src/tail.c (any_live_files): Simplify, since the IGNORE
flag is now only set when a file should be ignored indefinitely.
(recheck): Only output the "giving up on name" message
when that's actually the case.  Only set the IGNORE flag
when ignoring a file indefinitely.
(tail_file): Likewise.
* tests/tail-2/retry.sh: Add a test case.  Also run
all existing test cases with and without inotify.
NEWS: Mention the fix.
THANKS.in: Add the reporter.
Fixes http://bugs.gnu.org/24495 which was detected
using Symbolic Execution techniques developed in
the course of the SYMBIOSYS research project at
COMSYS, RWTH Aachen University.

4 files changed, 59 insertions, 24 deletions

diff --git a/NEWS b/NEWS
index beba7742e..c3554d0fe 100644
--- a/NEWS
+++ b/NEWS
@@ -42,6 +42,11 @@ GNU coreutils NEWS                                    -*- outline -*-
   seq now immediately exits upon write errors.
   [This bug was present in "the beginning".]
 
+  tail -F now continues to process initially untailable files that are replaced
+  by a tailable file.  This was handled correctly when inotify was available,
+  and is now handled correctly in all cases.
+  [bug introduced in fileutils-4.0h]
+
   yes now handles short writes, rather than assuming all writes complete.
   [bug introduced in coreutils-8.24]
 
diff --git a/THANKS.in b/THANKS.in
index a5fe80092..2109d75f3 100644
--- a/THANKS.in
+++ b/THANKS.in
@@ -330,6 +330,7 @@ Josselin Mouette                    joss@debian.org
 Juan F. Codagnone                   juam@arnet.com.ar
 Juan M. Guerrero                    st001906@hrz1.hrz.tu-darmstadt.de
 Julian Bradfield                    jcb@inf.ed.ac.uk
+Julian Büning                       julian.buening@rwth-aachen.de
 Jungshik Shin                       jshin@pantheon.yale.edu
 Juraj Marko                         jmarko@redhat.com
 Jürgen Fluk                         louis@dachau.marco.de
diff --git a/src/tail.c b/src/tail.c
index caa54076a..545da033c 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -956,8 +956,8 @@ recheck (struct File_spec *f, bool blocking)
       f->errnum = -1;
       f->ignore = true;
 
-      error (0, 0, _("%s has been replaced with a symbolic link. "
-                     "giving up on this name"), quoteaf (pretty_name (f)));
+      error (0, 0, _("%s has been replaced with an untailable symbolic link"),
+             quoteaf (pretty_name (f)));
     }
   else if (fd == -1 || fstat (fd, &new_stats) < 0)
     {
@@ -986,17 +986,20 @@ recheck (struct File_spec *f, bool blocking)
     {
       ok = false;
       f->errnum = -1;
-      error (0, 0, _("%s has been replaced with an untailable file;\
- giving up on this name"),
-             quoteaf (pretty_name (f)));
-      f->ignore = true;
+      f->tailable = false;
+      if (! (reopen_inaccessible_files && follow_mode == Follow_name))
+        f->ignore = true;
+      if (was_tailable || prev_errnum != f->errnum)
+        error (0, 0, _("%s has been replaced with an untailable file%s"),
+               quoteaf (pretty_name (f)),
+               f->ignore ? _("; giving up on this name") : "");
     }
   else if (!disable_inotify && fremote (fd, pretty_name (f)))
     {
       ok = false;
       f->errnum = -1;
-      error (0, 0, _("%s has been replaced with a remote file. "
-                     "giving up on this name"), quoteaf (pretty_name (f)));
+      error (0, 0, _("%s has been replaced with an untailable remote file"),
+             quoteaf (pretty_name (f)));
       f->ignore = true;
       f->remote = true;
     }
@@ -1075,20 +1078,20 @@ any_live_files (const struct File_spec *f, size_t n_files)
 {
   size_t i;
 
+  /* In inotify mode, ignore may be set for files
+     which may later be replaced with new files.
+     So always consider files live in -F mode.  */
   if (reopen_inaccessible_files && follow_mode == Follow_name)
-    return true;  /* continue following for -F option */
+    return true;
 
   for (i = 0; i < n_files; i++)
     {
       if (0 <= f[i].fd)
-        {
-          return true;
-        }
+        return true;
       else
         {
-          if (reopen_inaccessible_files && follow_mode == Follow_descriptor)
-            if (! f[i].ignore)
-              return true;
+          if (! f[i].ignore && reopen_inaccessible_files)
+            return true;
         }
     }
 
@@ -1930,12 +1933,14 @@ tail_file (struct File_spec *f, uintmax_t n_units)
             }
           else if (!IS_TAILABLE_FILE_TYPE (stats.st_mode))
             {
-              error (0, 0, _("%s: cannot follow end of this type of file;\
- giving up on this name"),
-                     quotef (pretty_name (f)));
               ok = false;
               f->errnum = -1;
-              f->ignore = true;
+              f->tailable = false;
+              f->ignore = ! (reopen_inaccessible_files
+                             && follow_mode == Follow_name);
+              error (0, 0, _("%s: cannot follow end of this type of file%s"),
+                     quotef (pretty_name (f)),
+                     f->ignore ? _("; giving up on this name") : "");
             }
 
           if (!ok)
diff --git a/tests/tail-2/retry.sh b/tests/tail-2/retry.sh
index 37e01edd6..a4cff11e6 100755
--- a/tests/tail-2/retry.sh
+++ b/tests/tail-2/retry.sh
@@ -55,11 +55,14 @@ tail --retry missing > out 2>&1 && fail=1
 [ "$(countlines_)" = 2 ]                     || { cat out; fail=1; }
 grep -F 'tail: warning: --retry ignored' out || { cat out; fail=1; }
 
+for mode in '' '---disable-inotify'; do
+
 # === Test:
 # Ensure that "tail --retry --follow=name" waits for the file to appear.
 # Clear 'out' so that we can check its contents without races
 >out                            || framework_failure_
-timeout 10 tail $fastpoll --follow=name --retry missing >out 2>&1 & pid=$!
+timeout 10 \
+  tail $mode $fastpoll --follow=name --retry missing >out 2>&1 & pid=$!
 # Wait for "cannot open" error.
 retry_delay_ wait4lines_ .1 6 1 || { cat out; fail=1; }
 echo "X" > missing              || framework_failure_
@@ -76,7 +79,8 @@ rm -f missing out          || framework_failure_
 # === Test:
 # Ensure that "tail --retry --follow=descriptor" waits for the file to appear.
 # tail-8.21 failed at this (since the implementation of the inotify support).
-timeout 10 tail $fastpoll --follow=descriptor --retry missing >out 2>&1 & pid=$!
+timeout 10 \
+  tail $mode $fastpoll --follow=descriptor --retry missing >out 2>&1 & pid=$!
 # Wait for "cannot open" error.
 retry_delay_ wait4lines_ .1 6 2 || { cat out; fail=1; }
 echo "X" > missing              || framework_failure_
@@ -95,7 +99,8 @@ rm -f missing out          || framework_failure_
 # === Test:
 # Ensure that tail --follow=descriptor --retry exits when the file appears
 # untailable. Expect exit status 1.
-timeout 10 tail $fastpoll --follow=descriptor --retry missing >out 2>&1 & pid=$!
+timeout 10 \
+  tail $mode $fastpoll --follow=descriptor --retry missing >out 2>&1 & pid=$!
 # Wait for "cannot open" error.
 retry_delay_ wait4lines_ .1 6 2 || { cat out; fail=1; }
 mkdir missing                   || framework_failure_  # Create untailable
@@ -116,16 +121,35 @@ rm -fd missing out                             || framework_failure_
 # Ensure that --follow=descriptor (without --retry) does *not wait* for the
 # file to appear.  Expect 2 lines in the output file ("cannot open" +
 # "no files remaining") and exit status 1.
-tail --follow=descriptor missing >out 2>&1 && fail=1
+tail $mode --follow=descriptor missing >out 2>&1 && fail=1
 [ "$(countlines_)" = 2 ]         || { fail=1; cat out; }
 grep -F 'cannot open' out        || { fail=1; cat out; }
 grep -F 'no files remaining' out || { fail=1; cat out; }
 
 # === Test:
 # Likewise for --follow=name (without --retry).
-tail --follow=name missing >out 2>&1 && fail=1
+tail $mode --follow=name missing >out 2>&1 && fail=1
 [ "$(countlines_)" = 2 ]         || { fail=1; cat out; }
 grep -F 'cannot open' out        || { fail=1; cat out; }
 grep -F 'no files remaining' out || { fail=1; cat out; }
 
+# === Test:
+# Ensure that tail -F retries when the file is initally untailable.
+mkdir untailable
+timeout 10 \
+  tail $mode $fastpoll -F untailable >out 2>&1 & pid=$!
+# Wait for "cannot open" error.
+retry_delay_ wait4lines_ .1 6 2 || { cat out; fail=1; }
+{ rmdir untailable; echo foo > untailable; }   || framework_failure_
+# Wait for the expected output.
+retry_delay_ wait4lines_ .1 6 4 || { cat out; fail=1; }
+cleanup_
+[ "$(countlines_)" = 4 ]                       || { fail=1; cat out; }
+grep -F 'cannot follow' out                    || { fail=1; cat out; }
+grep -F 'has become accessible' out            || { fail=1; cat out; }
+grep -F 'foo' out                              || { fail=1; cat out; }
+rm -fd untailable out                          || framework_failure_
+
+done
+
 Exit $fail