Fix appending to archive with changed blocking factor.

* src/buffer.c (flush_archive): If previous reading attempt resulted
in short read, correctly use the remaining record space.
(backspace_output): Fix position calculation (still has to be
improved).

* tests/append05.at: New test case.
* tests/Makefile.am: Add new test.
* tests/testsuite.at: Likewise.

src/buffer.c

@@ -983,18 +983,28 @@ short_read (size_t status)
 void
 flush_archive (void)
 {
-  size_t buffer_level = current_block->buffer - record_start->buffer;
-  record_start_block += record_end - record_start;
-  current_block = record_start;
-  record_end = record_start + blocking_factor;
-
+  size_t buffer_level;
+  
   if (access_mode == ACCESS_READ && time_to_start_writing)
     {
       access_mode = ACCESS_WRITE;
       time_to_start_writing = false;
       backspace_output ();
+      if (record_end - record_start < blocking_factor)
+	{
+	  memset (record_end, 0,
+		  (blocking_factor - (record_end - record_start))
+		  * BLOCKSIZE);
+	  record_end = record_start + blocking_factor;
+	  return;
+	}
     }
 
+  buffer_level = current_block->buffer - record_start->buffer;
+  record_start_block += record_end - record_start;
+  current_block = record_start;
+  record_end = record_start + blocking_factor;
+
   switch (access_mode)
     {
     case ACCESS_READ:
@@ -1034,7 +1044,7 @@ backspace_output (void)
 
     /* Seek back to the beginning of this record and start writing there.  */
 
-    position -= record_size;
+    position -= record_end->buffer - record_start->buffer;
     if (position < 0)
       position = 0;
     if (rmtlseek (archive, position, SEEK_SET) != position)

tests/Makefile.am

@@ -60,6 +60,7 @@ TESTSUITE_AT = \
  append02.at\
  append03.at\
  append04.at\
+ append05.at\
  backup01.at\
  chtype.at\
  comprec.at\

tests/append.at

@@ -27,7 +27,7 @@ AT_TAR_CHECK([touch file1
           tar cf archive file1
           tar rf archive file2
           tar tf archive],
-          [0],
+           [0],
 [file1
 file2
 ])

tests/append05.at

@@ -0,0 +1,96 @@
+# Process this file with autom4te to create testsuite. -*- Autotest -*-
+#
+# Test suite for GNU tar.
+# Copyright 2016 Free Software Foundation, Inc.
+#
+# This file is part of GNU tar.
+#
+# GNU tar 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.
+#
+# GNU tar 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/>.
+
+# Adding files to an archive with a blocking factor different from the one
+# used when creating it would produce a malformed archive.
+#
+# Last-Affected-Version: 1.28.90 (da7845c6563e7337bf3e8364046a7989091f190e)
+# Reported-by: Initial report by Renate Pyhel <rpyhel@google.com>.  Explained
+#   in detail by Tim Kientzle.  This test case is based on his posting.
+# References: <CALyyU7QJRQEQWMqZ=J=ppu-nwOH6R58Ci2ZkV32+CeZKsWsz7Q@mail.gmail.com>,
+#   <50202013-27F2-4EFF-98C8-2DD112C5B956@kientzle.com>,
+#   http://lists.gnu.org/archive/html/bug-tar/2016-03/msg00002.html,
+#   http://lists.gnu.org/archive/html/bug-tar/2016-03/msg00004.html
+
+AT_SETUP([append after changed blocking])
+AT_KEYWORDS([append append05 blocking])
+
+AT_TAR_CHECK([
+for f in a b c d e f g h i
+do
+  echo $f > $f
+done
+
+decho 'creating archive'
+tar -cf archive -b1 a b c
+
+tar tf archive
+
+decho 'adding d e f'
+tar -vrf archive -b3 d e f
+echo ==
+tar tf archive
+
+decho 'adding g h i'
+tar -vrf archive -b5 g h i
+
+decho 'resulting archive'
+tar tf archive
+],
+[0],
+[creating archive
+a
+b
+c
+adding d e f
+d
+e
+f
+==
+a
+b
+c
+d
+e
+f
+adding g h i
+g
+h
+i
+resulting archive
+a
+b
+c
+d
+e
+f
+g
+h
+i
+],
+[creating archive
+adding d e f
+adding g h i
+resulting archive
+])
+
+AT_CLEANUP
+
+

tests/testsuite.at

@@ -243,6 +243,7 @@ m4_include([append01.at])
 m4_include([append02.at])
 m4_include([append03.at])
 m4_include([append04.at])
+m4_include([append05.at])
 
 AT_BANNER([Transforms])
 m4_include([xform-h.at])