@cindex @samp{Ignoring unknown extended header keyword `%s'}, warning message
@item unknown-keyword
@samp{Ignoring unknown extended header keyword `%s'}
+@kwindex decompress-program
+@item decompress-program
+Controls verbose messages describing execution failures when trying
+alternative decompressor programs (@pxref{alternative decompression
+programs}). This warning is disabled by default (unless
+@option{--verbose} is used). A common example of what you can get
+when using this warning is:
+
+@smallexample
+$ @kbd{tar --warning=decompress-program -x -f archive.Z}
+tar (child): cannot run compress: No such file or directory
+tar (child): trying gzip
+@end smallexample
+
+This means that @command{tar} first tried to decompress
+@file{archive.Z} using @command{compress}, and, when that
+failed, switched to @command{gzip}.
@end table
@subheading Keywords controlling incremental extraction:
falls back to using archive name suffix to determine its format
(@pxref{auto-compress}, for a list of recognized suffixes).
+@anchor{alternative decompression programs}
+@cindex alternative decompression programs
+Some compression programs are able to handle different compression
+formats. @GNUTAR{} uses this, if the principal decompressor for the
+given format is not available. For example, if @command{compress} is
+not installed, @command{tar} will try to use @command{gzip}. As of
+version @value{VERSION} the following alternatives are
+tried@footnote{To verbosely trace the decompressor selection, use the
+@option{--warning=decompress-program} option
+(@pxref{warnings,decompress-program}).}:
+
+@multitable @columnfractions 0.3 0.3 0.3
+@headitem Format @tab Main decompressor @tab Alternatives
+@item compress @tab compress @tab gzip
+@item lzma @tab lzma @tab xz
+@item bzip2 @tab bzip2 @tab lbzip2
+@end multitable
+
The only case when you have to specify a decompression option while
reading the archive is when reading from a pipe or from a tape drive
that does not support random access. However, in this case @GNUTAR{}
/* Compression detection */
enum compress_type {
- ct_tar, /* Plain tar file */
ct_none, /* Unknown compression type */
+ ct_tar, /* Plain tar file */
ct_compress,
ct_gzip,
ct_bzip2,
ct_xz
};
+static enum compress_type archive_compression_type = ct_none;
+
struct zip_magic
{
enum compress_type type;
size_t length;
char const *magic;
+};
+
+struct zip_program
+{
+ enum compress_type type;
char const *program;
char const *option;
};
static struct zip_magic const magic[] = {
- { ct_tar },
{ ct_none, },
- { ct_compress, 2, "\037\235", COMPRESS_PROGRAM, "-Z" },
- { ct_gzip, 2, "\037\213", GZIP_PROGRAM, "-z" },
- { ct_bzip2, 3, "BZh", BZIP2_PROGRAM, "-j" },
- { ct_lzip, 4, "LZIP", LZIP_PROGRAM, "--lzip" },
- { ct_lzma, 6, "\xFFLZMA", LZMA_PROGRAM, "--lzma" },
- { ct_lzop, 4, "\211LZO", LZOP_PROGRAM, "--lzop" },
- { ct_xz, 6, "\xFD" "7zXZ", XZ_PROGRAM, "-J" },
+ { ct_tar },
+ { ct_compress, 2, "\037\235" },
+ { ct_gzip, 2, "\037\213" },
+ { ct_bzip2, 3, "BZh" },
+ { ct_lzip, 4, "LZIP" },
+ { ct_lzma, 6, "\xFFLZMA" },
+ { ct_lzop, 4, "\211LZO" },
+ { ct_xz, 6, "\xFD" "7zXZ" },
};
#define NMAGIC (sizeof(magic)/sizeof(magic[0]))
-#define compress_option(t) magic[t].option
-#define compress_program(t) magic[t].program
+static struct zip_program zip_program[] = {
+ { ct_compress, COMPRESS_PROGRAM, "-Z" },
+ { ct_compress, GZIP_PROGRAM, "-z" },
+ { ct_gzip, GZIP_PROGRAM, "-z" },
+ { ct_bzip2, BZIP2_PROGRAM, "-j" },
+ { ct_bzip2, "lbzip2", "-j" },
+ { ct_lzip, LZIP_PROGRAM, "--lzip" },
+ { ct_lzma, LZMA_PROGRAM, "--lzma" },
+ { ct_lzma, XZ_PROGRAM, "-J" },
+ { ct_lzop, LZOP_PROGRAM, "--lzop" },
+ { ct_xz, XZ_PROGRAM, "-J" },
+ { ct_none }
+};
+
+static struct zip_program const *
+find_zip_program (enum compress_type type, int *pstate)
+{
+ int i;
+
+ for (i = *pstate; zip_program[i].type != ct_none; i++)
+ {
+ if (zip_program[i].type == type)
+ {
+ *pstate = i + 1;
+ return zip_program + i;
+ }
+ }
+ *pstate = i;
+ return NULL;
+}
+
+const char *
+first_decompress_program (int *pstate)
+{
+ struct zip_program const *zp;
+
+ if (use_compress_program_option)
+ return use_compress_program_option;
+
+ if (archive_compression_type == ct_none)
+ return NULL;
+
+ *pstate = 0;
+ zp = find_zip_program (archive_compression_type, pstate);
+ return zp ? zp->program : NULL;
+}
+
+const char *
+next_decompress_program (int *pstate)
+{
+ struct zip_program const *zp;
+
+ if (use_compress_program_option)
+ return NULL;
+ zp = find_zip_program (archive_compression_type, pstate);
+ return zp ? zp->program : NULL;
+}
+
+static const char *
+compress_option (enum compress_type type)
+{
+ struct zip_program const *zp;
+ int i = 0;
+ zp = find_zip_program (type, &i);
+ return zp ? zp->option : NULL;
+}
/* Check if the file ARCHIVE is a compressed archive. */
static enum compress_type
break;
default:
- use_compress_program_option = compress_program (type);
+ archive_compression_type = type;
break;
}
}
wait_for_grandchild (grandchild_pid);
}
+static void
+run_decompress_program (void)
+{
+ int i;
+ const char *p, *prog = NULL;
+
+ for (p = first_decompress_program (&i); p; p = next_decompress_program (&i))
+ {
+ if (prog)
+ {
+ WARNOPT (WARN_DECOMPRESS_PROGRAM,
+ (0, errno, _("cannot run %s"), prog));
+ WARNOPT (WARN_DECOMPRESS_PROGRAM,
+ (0, 0, _("trying %s"), p));
+ }
+ prog = p;
+ execlp (p, p, "-d", NULL);
+ }
+ if (!prog)
+ FATAL_ERROR ((0, 0, _("unable to run decompression program")));
+ exec_fatal (prog);
+}
+
/* Set ARCHIVE for uncompressing, then reading an archive. */
pid_t
sys_child_open_for_uncompress (void)
open_fatal (archive_name_array[0]);
xdup2 (archive, STDIN_FILENO);
priv_set_restore_linkdir ();
- execlp (use_compress_program_option, use_compress_program_option,
- "-d", (char *) 0);
- exec_fatal (use_compress_program_option);
+ run_decompress_program ();
}
/* We do need a grandchild tar. */
xdup2 (child_pipe[PREAD], STDIN_FILENO);
xclose (child_pipe[PWRITE]);
priv_set_restore_linkdir ();
- execlp (use_compress_program_option, use_compress_program_option,
- "-d", (char *) 0);
- exec_fatal (use_compress_program_option);
+ run_decompress_program ();
}
/* The child tar is still here! */
projects / chaz / tar / commitdiff
