Fix a bug in multi-volume archive creation.

When creating multivolume archives, the bufmap code in buffer.c
implicitly assumed that the members are stored in the archive
contiguously, ignoring the member (and eventual extended) headers
between them.  This worked until the member header happened to be
at the very beginning of the volume, in which case its length was
included in the calculation of the stored size and size left to
store.  Due to this, the GNUFileParts extended header contained
invalid GNU.volume.offset value, and the resulting archive failed
to extract properly.

This patch also eliminates improper listing of file part headers
as regular files, when creating multivolume posix archives with -v.

* src/buffer.c (bufmap): New member nblocks.  Counts number of blocks
of file data written since reset.
(bufmap_reset): Reset nblocks to 0.
(_flush_write): Update nblocks.  When computing offset difference for
bufmap_reset, count only data blocks, not headers.
(close_archive): Flush archive until all blocks are written.
(add_chunk_header): Use simple_finish_header instead of finish_header
to avoid listing chunk header as regular file in verbose mode.
* tests/multiv10.at: New test case.
* tests/Makefile.am: Add new test.
* tests/testsuite.at: Add new test.

src/buffer.c

@@ -105,13 +105,20 @@ bool write_archive_to_stdout;
 
 /* When creating a multi-volume archive, each 'bufmap' represents
    a member stored (perhaps partly) in the current record buffer.
+   Bufmaps are form a single-linked list in chronological order.
+   
    After flushing the record to the output media, all bufmaps that
-   represent fully written members are removed from the list, then
-   the sizeleft and start numbers in the remaining bufmaps are updated.
+   represent fully written members are removed from the list, the
+   nblocks and sizeleft values in the bufmap_head and start values
+   in all remaining bufmaps are updated.  The information stored
+   in bufmap_head is used to form the volume header.
 
    When reading from a multi-volume archive, the list degrades to a
    single element, which keeps information about the member currently
-   being read.
+   being read.  In that case the sizeleft member is updated explicitly
+   from the extractor code by calling the mv_size_left function.  The
+   information from bufmap_head is compared with the volume header data
+   to ensure that subsequent volumes are fed in the right order.
 */
 
 struct bufmap
@@ -121,6 +128,7 @@ struct bufmap
   char *file_name;              /* Name of the stored file */
   off_t sizetotal;              /* Size of the stored file */
   off_t sizeleft;               /* Size left to read/write */
+  size_t nblocks;               /* Number of blocks written since reset */
 };
 static struct bufmap *bufmap_head, *bufmap_tail;
 
@@ -145,6 +153,7 @@ mv_begin_write (const char *file_name, off_t totsize, off_t sizeleft)
       bp->file_name = xstrdup (file_name);
       bp->sizetotal = totsize;
       bp->sizeleft = sizeleft;
+      bp->nblocks = 0;
     }
 }
 
@@ -155,8 +164,7 @@ bufmap_locate (size_t off)
 
   for (map = bufmap_head; map; map = map->next)
     {
-      if (!map->next
-	  || off < map->next->start * BLOCKSIZE)
+      if (!map->next || off < map->next->start * BLOCKSIZE)
 	break;
     }
   return map;
@@ -185,7 +193,10 @@ bufmap_reset (struct bufmap *map, ssize_t fixup)
   if (map)
     {
       for (; map; map = map->next)
-	map->start += fixup;
+	{
+	  map->start += fixup;
+	  map->nblocks = 0;
+	}
     }
 }
 
@@ -868,12 +879,19 @@ _flush_write (void)
       if (map)
 	{
 	  size_t delta = status - map->start * BLOCKSIZE;
+	  ssize_t diff;
+	  map->nblocks += delta / BLOCKSIZE;
 	  if (delta > map->sizeleft)
 	    delta = map->sizeleft;
 	  map->sizeleft -= delta;
 	  if (map->sizeleft == 0)
-	    map = map->next;
-	  bufmap_reset (map, map ? (- map->start) : 0);
+	    {
+	      diff = map->start + map->nblocks;
+	      map = map->next;
+	    }
+	  else
+	    diff = map->start;
+	  bufmap_reset (map, - diff);
 	}
     }
   return status;
@@ -1105,9 +1123,9 @@ close_archive (void)
 {
   if (time_to_start_writing || access_mode == ACCESS_WRITE)
     {
-      flush_archive ();
-      if (current_block > record_start)
-        flush_archive ();
+      do
+	flush_archive ();
+      while (current_block > record_start);
     }
 
   compute_duration ();
@@ -1711,7 +1729,6 @@ add_chunk_header (struct bufmap *map)
 {
   if (archive_format == POSIX_FORMAT)
     {
-      off_t block_ordinal;
       union block *blk;
       struct tar_stat_info st;
 
@@ -1726,11 +1743,10 @@ add_chunk_header (struct bufmap *map)
       st.file_name = st.orig_file_name;
       st.archive_file_size = st.stat.st_size = map->sizeleft;
 
-      block_ordinal = current_block_ordinal ();
       blk = start_header (&st);
       if (!blk)
         abort (); /* FIXME */
-      finish_header (&st, blk, block_ordinal);
+      simple_finish_header (write_extended (false, &st, blk));
       free (st.orig_file_name);
     }
 }