tar: handle files that occur multiple times but have link count 1

This patch was inspired by the following patch that addressed a
similar problem in GNU coreutils du:
http://git.savannah.gnu.org/gitweb/?p=coreutils.git;h=efe53cc72b599979ea292754ecfe8abf7c839d22
* src/common.h (name_count): New decl.
* src/create.c (trivial_link_count): New static var.
(create_archive): Initialize it.
(dump_hard_link, file_count_links): Use it, so that files with
link count 1 are handled correctly when they are found multiple times.
* src/names.c (allocated_entries): Renamed from allocated_names,
since the identifier's name was misleading.  All uses changed.
(entries): Renamed from names.  All uses changed.
(scanned): Renamed from name_index.  All uses changed.
(name_count): New var.
(name_add_name): Increment it.
* tests/link04.at: New file.
* tests/testsuite.at: Add it.
* tests/Makefile.am (TESTSUITE_AT): Likewise.

src/common.h

@@ -636,6 +636,7 @@ int set_file_atime (int fd, char const *file,
 
 /* Module names.c.  */
 
+extern size_t name_count;
 extern struct name *gnu_list_name;
 
 void gid_to_gname (gid_t gid, char **gname);

src/create.c

@@ -1265,6 +1265,12 @@ dump_dir (int fd, struct tar_stat_info *st, bool top_level,
   return true;
 }
 
+
+/* Number of links a file can have without having to be entered into
+   the link table.  Typically this is 1, but in trickier circumstances
+   it is 0.  */
+static nlink_t trivial_link_count;
+
 
 /* Main functions of this module.  */
 
@@ -1273,6 +1279,8 @@ create_archive (void)
 {
   struct name const *p;
 
+  trivial_link_count = name_count <= 1 && ! dereference_option;
+
   open_archive (ACCESS_WRITE);
   buffer_write_global_xheader ();
 
@@ -1380,7 +1388,8 @@ static Hash_table *link_table;
 static bool
 dump_hard_link (struct tar_stat_info *st)
 {
-  if (link_table && (st->stat.st_nlink > 1 || remove_files_option))
+  if (link_table
+      && (trivial_link_count < st->stat.st_nlink || remove_files_option))
     {
       struct link lp;
       struct link *duplicate;
@@ -1427,7 +1436,7 @@ file_count_links (struct tar_stat_info *st)
 {
   if (hard_dereference_option)
     return;
-  if (st->stat.st_nlink > 1)
+  if (trivial_link_count < st->stat.st_nlink)
     {
       struct link *duplicate;
       char *linkname = NULL;

src/names.c

@@ -226,19 +226,20 @@ struct name_elt        /* A name_array element. */
 };
 
 static struct name_elt *name_array;  /* store an array of names */
-static size_t allocated_names;	 /* how big is the array? */
-static size_t names;		 /* how many entries does it have? */
-static size_t name_index;	 /* how many of the entries have we scanned? */
+static size_t allocated_entries; /* how big is the array? */
+static size_t entries;		 /* how many entries does it have? */
+static size_t scanned;		 /* how many of the entries have we scanned? */
+size_t name_count;		 /* how many of the entries are names? */
 
 /* Check the size of name_array, reallocating it as necessary.  */
 static void
 check_name_alloc (void)
 {
-  if (names == allocated_names)
+  if (entries == allocated_entries)
     {
-      if (allocated_names == 0)
-	allocated_names = 10; /* Set initial allocation */
-      name_array = x2nrealloc (name_array, &allocated_names,
+      if (allocated_entries == 0)
+	allocated_entries = 10; /* Set initial allocation */
+      name_array = x2nrealloc (name_array, &allocated_entries,
 			       sizeof (name_array[0]));
     }
 }
@@ -251,17 +252,18 @@ name_add_name (const char *name, int matching_flags)
   struct name_elt *ep;
 
   check_name_alloc ();
-  ep = &name_array[names++];
+  ep = &name_array[entries++];
   if (prev_flags != matching_flags)
     {
       ep->type = NELT_FMASK;
       ep->v.matching_flags = matching_flags;
       prev_flags = matching_flags;
       check_name_alloc ();
-      ep = &name_array[names++];
+      ep = &name_array[entries++];
     }
   ep->type = NELT_NAME;
   ep->v.name = name;
+  name_count++;
 }
 
 /* Add to name_array a chdir request for the directory NAME */
@@ -270,7 +272,7 @@ name_add_dir (const char *name)
 {
   struct name_elt *ep;
   check_name_alloc ();
-  ep = &name_array[names++];
+  ep = &name_array[entries++];
   ep->type = NELT_CHDIR;
   ep->v.name = name;
 }
@@ -314,12 +316,12 @@ name_next_elt (int change_dirs)
   const char *source;
   char *cursor;
 
-  while (name_index != names)
+  while (scanned != entries)
     {
       struct name_elt *ep;
       size_t source_len;
 
-      ep = &name_array[name_index++];
+      ep = &name_array[scanned++];
       if (ep->type == NELT_FMASK)
 	{
 	  matching_flags = ep->v.matching_flags;