Fix semantics of -K used together with explicit member names.

This also fixes the bug reported in
  http://lists.gnu.org/archive/html/bug-tar/2018-12/msg00012.html

* src/common.h (starting_file_option): Describe the variable.
* src/names.c (add_starting_file): New function.
(name_match): Ignore everything before the member indicated by the
--starting-file option
* src/tar.c: Use add_starting_file to handle the -K option.

src/common.h

@@ -302,6 +302,10 @@ enum hole_detection_method
 
 GLOBAL enum hole_detection_method hole_detection;
 
+/* The first entry in names.c:namelist specifies the member name to
+   start extracting from. Set by add_starting_file() upon seeing the
+   -K option.
+*/
 GLOBAL bool starting_file_option;
 
 /* Specified maximum byte length of each tape volume (multiple of 1024).  */
@@ -752,6 +756,7 @@ const char *name_next (int change_dirs);
 void name_gather (void);
 struct name *addname (char const *string, int change_dir,
 		      bool cmdline, struct name *parent);
+void add_starting_file (char const *file_name);
 void remname (struct name *name);
 bool name_match (const char *name);
 void names_notfound (void);

src/names.c

@@ -1227,6 +1227,34 @@ addname (char const *string, int change_dir, bool cmdline, struct name *parent)
   return name;
 }
 
+void
+add_starting_file (char const *file_name)
+{
+  struct name *name = make_name (file_name);
+
+  if (starting_file_option)
+    {
+      struct name *head = namelist;
+      remname (head);
+      free_name (head);
+    }
+  
+  name->prev = NULL;
+  name->next = namelist;
+  namelist = name;
+  if (!nametail)
+    nametail = namelist;
+  
+  name->found_count = 0;
+  name->matching_flags = INCLUDE_OPTIONS;
+  name->change_dir = 0;
+  name->directory = NULL;
+  name->parent = NULL;
+  name->cmdline = true;
+
+  starting_file_option = true;
+}
+
 /* Find a match for FILE_NAME (whose string length is LENGTH) in the name
    list.  */
 static struct name *
@@ -1283,19 +1311,22 @@ name_match (const char *file_name)
 	}
 
       cursor = namelist_match (file_name, length);
+      if (starting_file_option)
+	{
+	  /* If starting_file_option is set, the head of the list is the name
+	     of the member to start extraction from. Skip the match unless it
+	     is head. */
+	  if (cursor == namelist)
+	    starting_file_option = false;
+	  else
+	    cursor = NULL;
+	}
       if (cursor)
 	{
 	  if (!(ISSLASH (file_name[cursor->length]) && recursion_option)
 	      || cursor->found_count == 0)
 	    cursor->found_count++; /* remember it matched */
-	  if (starting_file_option)
-	    {
-	      free (namelist);
-	      namelist = NULL;
-	      nametail = NULL;
-	    }
 	  chdir_do (cursor->change_dir);
-
 	  /* We got a match.  */
 	  return ISFOUND (cursor);
 	}

src/tar.c

@@ -1443,8 +1443,7 @@ parse_opt (int key, char *arg, struct argp_state *state)
 
     case 'K':
       optloc_save (OC_STARTING_FILE, args->loc);
-      starting_file_option = true;
-      addname (arg, 0, true, NULL);
+      add_starting_file (arg);
       break;
 
     case ONE_FILE_SYSTEM_OPTION: