Optionally warn about missing zero blocks at the end of the archive

(In response to savannah bug #63574)

* doc/intern.texi: Document actual tar behaviour in regard to
missing end-of-file marker.
* doc/tar.texi: Rewrite the "warnings" section.  Document
--warning=missing-zero-blocks
* src/common.h (WARN_MISSING_ZERO_BLOCKS): New constant.
(WARN_ALL): Include all warning bits.
* src/list.c (read_and): If EOF is reached without seeing end-of-file
blocks and the "missing-zero-blocks" warning is requested, warn about
the fact.
* src/warning.c: New warnings: "missing-zero-blocks", "verbose".
(warning_option): Change definition to reflect changes in common.h

src/common.h

@@ -987,12 +987,13 @@ void checkpoint_flush_actions (void);
 #define WARN_XATTR_WRITE         0x00200000
 #define WARN_RECORD_SIZE         0x00400000
 #define WARN_FAILED_READ         0x00800000
+#define WARN_MISSING_ZERO_BLOCKS 0x01000000
 
 /* These warnings are enabled by default in verbose mode: */
 #define WARN_VERBOSE_WARNINGS    (WARN_RENAME_DIRECTORY|WARN_NEW_DIRECTORY|\
 				  WARN_DECOMPRESS_PROGRAM|WARN_EXISTING_FILE|\
 		                  WARN_RECORD_SIZE)
-#define WARN_ALL                 (~WARN_VERBOSE_WARNINGS)
+#define WARN_ALL                 0xffffffff
 
 void set_warning_option (const char *arg);
 

src/list.c

@@ -256,6 +256,13 @@ read_and (void (*do_something) (void))
 	  continue;
 
 	case HEADER_END_OF_FILE:
+	  if (!ignore_zeros_option)
+	    {
+	      char buf[UINTMAX_STRSIZE_BOUND];
+	      WARNOPT (WARN_MISSING_ZERO_BLOCKS,
+		       (0, 0, _("Terminating zero blocks missing at %s"),
+			STRINGIFY_BIGINT (current_block_ordinal (), buf)));
+	    }
 	  if (block_number_option)
 	    {
 	      char buf[UINTMAX_STRSIZE_BOUND];

src/warning.c

@@ -48,6 +48,8 @@ static char const *const warning_args[] = {
   "xattr-write",
   "record-size",
   "failed-read",
+  "missing-zero-blocks",
+  "verbose",
   NULL
 };
 
@@ -76,12 +78,14 @@ static int warning_types[] = {
   WARN_EXISTING_FILE,
   WARN_XATTR_WRITE,
   WARN_RECORD_SIZE,
-  WARN_FAILED_READ
+  WARN_FAILED_READ,
+  WARN_MISSING_ZERO_BLOCKS,
+  WARN_VERBOSE_WARNINGS,
 };
 
 ARGMATCH_VERIFY (warning_args, warning_types);
 
-int warning_option = WARN_ALL;
+int warning_option = WARN_ALL & ~(WARN_VERBOSE_WARNINGS|WARN_MISSING_ZERO_BLOCKS);
 
 void
 set_warning_option (const char *arg)