Add support for zstd compression

* configure.ac (zstd): Register compression program.
* doc/tar.1: Mention --zstd.
* doc/tar.texi: Document zstd support.
* src/buffer.c: Register zstd compression.
* src/suffix.c: Add suffixes zst and tzst.
* src/tar.c: New compression option --zstd.

src/buffer.c

@@ -281,7 +281,8 @@ enum compress_type {
   ct_lzip,
   ct_lzma,
   ct_lzop,
-  ct_xz
+  ct_xz,
+  ct_zstd
 };
 
 static enum compress_type archive_compression_type = ct_none;
@@ -310,6 +311,7 @@ static struct zip_magic const magic[] = {
   { ct_lzma,     6, "\xFFLZMA" },
   { ct_lzop,     4, "\211LZO" },
   { ct_xz,       6, "\xFD" "7zXZ" },
+  { ct_zstd,     4, "\x28\xB5\x2F\xFD" },
 };
 
 #define NMAGIC (sizeof(magic)/sizeof(magic[0]))
@@ -325,6 +327,7 @@ static struct zip_program zip_program[] = {
   { ct_lzma,     XZ_PROGRAM,       "-J" },
   { ct_lzop,     LZOP_PROGRAM,     "--lzop" },
   { ct_xz,       XZ_PROGRAM,       "-J" },
+  { ct_zstd,     ZSTD_PROGRAM,     "--zstd" },
   { ct_none }
 };
 

src/suffix.c

@@ -46,6 +46,8 @@ static struct compression_suffix compression_suffixes[] = {
   { S(lzo,  LZOP) },
   { S(xz,   XZ) },
   { S(txz,  XZ) }, /* Slackware */
+  { S(zst,  ZSTD) },
+  { S(tzst, ZSTD) },
   { NULL }
 #undef S
 #undef __CAT2__

src/tar.c

@@ -348,7 +348,8 @@ enum
   WARNING_OPTION,
   XATTR_OPTION,
   XATTR_EXCLUDE,
-  XATTR_INCLUDE
+  XATTR_INCLUDE,
+  ZSTD_OPTION,
 };
 
 static char const doc[] = N_("\
@@ -682,6 +683,7 @@ static struct argp_option options[] = {
   {"lzma", LZMA_OPTION, 0, 0, NULL, GRID+1 },
   {"lzop", LZOP_OPTION, 0, 0, NULL, GRID+1 },
   {"xz", 'J', 0, 0, NULL, GRID+1 },
+  {"zstd", ZSTD_OPTION, 0, 0, NULL, GRID+1 },
 #undef GRID
 
 #define GRID 100
@@ -1129,6 +1131,10 @@ tar_help_filter (int key, const char *text, void *input)
       s = xasprintf (_("filter the archive through %s"), XZ_PROGRAM);
       break;
 
+    case ZSTD_OPTION:
+      s = xasprintf (_("filter the archive through %s"), ZSTD_PROGRAM);
+      break;
+
     case ARGP_KEY_HELP_EXTRA:
       {
 	const char *tstr;
@@ -1650,6 +1656,10 @@ parse_opt (int key, char *arg, struct argp_state *state)
       set_use_compress_program_option (COMPRESS_PROGRAM, args->loc);
       break;
 
+    case ZSTD_OPTION:
+      set_use_compress_program_option (ZSTD_PROGRAM, args->loc);
+      break;
+
     case ATIME_PRESERVE_OPTION:
       atime_preserve_option =
 	(arg