POSIX extended format headers do not include PID by default

The intent is to make binary-equivalent PAX archives easy to create.  If
POSIXLY_CORRECT is set, the POSIX standard default is used, which embeds
the pid.

* src/common.h (posixly_correct): New global.
* src/tar.c (decode_options): Detect the POSIXLY_CORRECT environment
variable.
* src/buffer.c (add_chunk_header): Change filenames of multipart files to
omit the pid.
* src/xheader.c (HEADER_TEMPLATE): New macro.
(xheader_xhdr_name, xheader_ghdr_name): Use HEADER_TEMPLATE to select
the template for the POSIX extended header name.
* doc/tar.texi: Document the change.

Signed-off-by: Zachary Vance <za3k@za3k.com>

src/buffer.c

@@ -1731,7 +1731,7 @@ add_chunk_header (struct bufmap *map)
       st.stat.st_uid = getuid ();
       st.stat.st_gid = getgid ();
       st.orig_file_name = xheader_format_name (&st,
-                                               "%d/GNUFileParts.%p/%f.%n",
+                                               "%d/GNUFileParts/%f.%n",
                                                volno);
       st.file_name = st.orig_file_name;
       st.archive_file_size = st.stat.st_size = map->sizeleft;

src/common.h

@@ -340,6 +340,9 @@ GLOBAL const char *volume_label_option;
 
 /* Other global variables.  */
 
+/* Force POSIX-compliance */
+GLOBAL bool posixly_correct;
+
 /* File descriptor for archive file.  */
 GLOBAL int archive;
 

src/tar.c

@@ -2230,6 +2230,8 @@ decode_options (int argc, char **argv)
   args.version_control_string = 0;
   args.compress_autodetect = false;
 
+  posixly_correct = getenv ("POSIXLY_CORRECT") != NULL;
+
   subcommand_option = UNKNOWN_SUBCOMMAND;
   archive_format = DEFAULT_FORMAT;
   blocking_factor = DEFAULT_BLOCKING;

src/xheader.c

@@ -369,29 +369,46 @@ xheader_format_name (struct tar_stat_info *st, const char *fmt, size_t n)
   return buf;
 }
 
+/* Table of templates for the names of POSIX extended headers.
+   Indexed by the the type of the header (per-file or global)
+   and POSIX compliance mode (0 or q depending on whether
+   POSIXLY_CORRECT environment variable is set. */
+static const char *header_template[][2] = {
+  /* Individual header templates: */
+  { "%d/PaxHeaders/%f", "%d/PaxHeaders.%p/%f" },
+  /* Global header templates: */
+  { "/GlobalHead.%n", "/GlobalHead.%p.%n" }
+};
+/* Indices to the above table */
+enum {
+  pax_file_header,
+  pax_global_header
+};
+/* Return the name for the POSIX extended header T */
+#define HEADER_TEMPLATE(t) header_template[t][posixly_correct]
+
 char *
 xheader_xhdr_name (struct tar_stat_info *st)
 {
   if (!exthdr_name)
-    assign_string (&exthdr_name, "%d/PaxHeaders.%p/%f");
+    assign_string (&exthdr_name, HEADER_TEMPLATE (pax_file_header));
   return xheader_format_name (st, exthdr_name, 0);
 }
 
-#define GLOBAL_HEADER_TEMPLATE "/GlobalHead.%p.%n"
-
 char *
 xheader_ghdr_name (void)
 {
   if (!globexthdr_name)
     {
       size_t len;
+      const char *global_header_template = HEADER_TEMPLATE (pax_global_header);
       const char *tmp = getenv ("TMPDIR");
       if (!tmp)
 	tmp = "/tmp";
-      len = strlen (tmp) + sizeof (GLOBAL_HEADER_TEMPLATE); /* Includes nul */
+      len = strlen (tmp) + strlen (global_header_template) + 1;
       globexthdr_name = xmalloc (len);
       strcpy(globexthdr_name, tmp);
-      strcat(globexthdr_name, GLOBAL_HEADER_TEMPLATE);
+      strcat(globexthdr_name, global_header_template);
     }
 
   return xheader_format_name (NULL, globexthdr_name, global_header_count + 1);