[Bug-tar] [PATCH] tar: do not fail hardly when compressor just warns

[Pavel Raiskup]

Obsolete the --use-compress-program by the --filter-program
option (same sematics).  Add new option --compress-program.

Use '--compres-program'-like API by the -Z, but also by -z, -J,
--lzop and --lzma options.  Use '--filter-program'-like interface
by -j and --lzip.

See also:
<http://lists.gnu.org/archive/html/bug-tar/2013-02/msg00025.html>
<http://lists.gnu.org/archive/html/bug-tar/2013-04/msg00006.html>
<https://bugzilla.redhat.com/show_bug.cgi?id=759371>

* src/common.h (compress_like_api): New global.
* src/tar.c (argp_option): Add --compress-program and
--filter-program options, obsolete --use-compress-program option.
(COMPRESS_PROGRAM_OPTION): New option in enum.
(tar_help_filter): Set 'compress_like_api' global for proper
compressors, handle new COMPRESS_PROGRAM_OPTION.
* src/system.c (sys_wait_for_child): Warn only when child process
exited with 2 and uses 'compress_like_api'.
* doc/tar.texi: Document all changes.
* NEWS: Document.
---
 NEWS         | 17 +++++++++++++++++
 doc/tar.texi | 32 ++++++++++++++++++++++++--------
 src/common.h |  3 +++
 src/system.c | 12 +++++++++---
 src/tar.c    | 22 ++++++++++++++++++++--
 5 files changed, 73 insertions(+), 13 deletions(-)

diff --git a/NEWS b/NEWS
index 3108798..7bba8e6 100644
--- a/NEWS
+++ b/NEWS
@@ -6,6 +6,23 @@ version 1.26.90 (Git)
 
 * Bug fixes
 
+** tar now successes when the compressor "warns" by exit status 2
+
+New options --filter-program and --compress-program were added.  The
+option --filter-program replaces the old --use-compress-program (which
+is now still working, but is obsoleted and removed from manual to not
+confuse users).  That means that program passed as an argument to
+--filter-program, apart from others requirements, must return zero
+exit status if successed, otherwise failed.  The --compress-program
+option is similar to --filter-program, but accepts also the child's
+exit value 2 as a correct (but warning) exit status.
+
+The default 'xz', 'gzip', 'compress', 'lzop' and 'lzma' compressors
+(used by -J, -z, -Z, --lzop and --lzma options) are now by default
+used by the --compress-program API; and compressors 'bzip2' and 'lzip'
+(used by -j and --lzip options) are used with more "vanilla"
+--filter-program API.
+
 ** Sparse files with large data
 
 When creating a PAX-format archive, tar no longer arbitrarily restricts
diff --git a/doc/tar.texi b/doc/tar.texi
index 480fe89..e300b54 100644
--- a/doc/tar.texi
+++ b/doc/tar.texi
@@ -3412,12 +3412,13 @@ system before extracting it from the archive.  
@xref{Unlink First}.
 Enable unquoting input file or member names (default).  @xref{input
 name quoting}.
 
address@hidden
address@hidden address@hidden
address@hidden
address@hidden address@hidden
 @itemx address@hidden
 
 Instructs @command{tar} to access the archive through @var{prog}, which is
-presumed to be a compression program of some sort.  @xref{gzip}.
+presumed to be a compression program of some sort.  This option obsoletes the
+old option @option{--use-compress-program}.  @xref{gzip}.
 
 @opsummary{utc}
 @item --utc
@@ -4284,7 +4285,7 @@ supply on the command line.  One of such operations is 
checkpointing,
 described above (@pxref{checkpoint exec}).  Another example of this
 feature is the @option{-I} option, which allows you to supply the
 program to use for compressing or decompressing the archive
-(@pxref{use-compress-program}).
+(@pxref{filter-program}).
 
 Whenever such operation is requested, @command{tar} first splits the
 supplied command into words much like the shell does.  It then treats
@@ -9053,9 +9054,9 @@ suffix.  The following suffixes are recognized:
 @item @samp{.xz} @tab @command{xz}
 @end multitable
 
address@hidden
address@hidden use-compress-program
address@hidden address@hidden
address@hidden
address@hidden filter-program
address@hidden address@hidden
 @itemx address@hidden
 Use external compression program @var{command}.  Use this option if you
 are not happy with the compression program associated with the suffix
@@ -9076,12 +9077,15 @@ standard input and produce uncompressed data on the 
standard output.
 
 The latter requirement means that you must not use the @option{-d}
 option as a part of the @var{command} itself.
+
+From the @GNUTAR{} point of view, any non-zero exit value of @var{command} is
+taken as a fatal error.
 @end table
 
 @cindex gpg, using with tar
 @cindex gnupg, using with tar
 @cindex Using encrypted archives
-The @option{--use-compress-program} option, in particular, lets you
+The @option{--filter-program} option, in particular, lets you
 implement your own filters, not necessarily dealing with
 compression/decompression.  For example, suppose you wish to implement
 PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
@@ -9152,6 +9156,18 @@ The above is based on the following discussion:
   the DLT compression mode, the data will actually get bigger and one will
   end up with less space on the tape.
 @end ignore
address@hidden @option
address@hidden
address@hidden compress-program
address@hidden address@hidden
+This option has exactly the same semantics as the previous
address@hidden with one exception.  When the @var{command} exits with
+exit status 2, this is considered like as warning - not a fatal error.  This
+option was created to allow user to pass compressor having similar interface as
+the @command{compress} has (exit status 2 warns that the "compressed" output
+is bigger than uncompressed input).  Other examples having such non-fatal exit
+status are @command{xz}, @command{lzma}, @command{gzip} or @command{lzop}.
address@hidden table
 
 @menu
 * lbzip2::  Using lbzip2 with @GNUTAR{}.
diff --git a/src/common.h b/src/common.h
index 4f7c19f..53790c3 100644
--- a/src/common.h
+++ b/src/common.h
@@ -145,6 +145,9 @@ GLOBAL unsigned checkpoint_option;
 /* Specified name of compression program, or "gzip" as implied by -z.  */
 GLOBAL const char *use_compress_program_option;
 
+/* The exit value 2 of compression program is not fatal error */
+GLOBAL bool compress_like_api;
+
 GLOBAL bool dereference_option;
 GLOBAL bool hard_dereference_option;
 
diff --git a/src/system.c b/src/system.c
index e1fd263..32bfd37 100644
--- a/src/system.c
+++ b/src/system.c
@@ -189,9 +189,15 @@ sys_wait_for_child (pid_t child_pid, bool eof)
          if (!(!eof && sig == SIGPIPE))
            FATAL_ERROR ((0, 0, _("Child died with signal %d"), sig));
        }
-      else if (WEXITSTATUS (wait_status) != 0)
-       FATAL_ERROR ((0, 0, _("Child returned status %d"),
-                     WEXITSTATUS (wait_status)));
+      else if (WEXITSTATUS (wait_status) == 0)
+        return;
+      /* compress-like api just warns by exit status 2 */
+      else if (WEXITSTATUS (wait_status) == 2 && compress_like_api)
+        WARN ((0, 0, _("%lu: Child '%s' exited with warning"),
+               (unsigned long) child_pid, use_compress_program_option));
+      else
+        FATAL_ERROR ((0, 0, _("Child '%s' returned exit status %d"),
+                      use_compress_program_option, WEXITSTATUS (wait_status)));
     }
 }
 
diff --git a/src/tar.c b/src/tar.c
index c29b4fa..a141b69 100644
--- a/src/tar.c
+++ b/src/tar.c
@@ -267,6 +267,7 @@ enum
   CHECK_DEVICE_OPTION,
   CHECKPOINT_OPTION,
   CHECKPOINT_ACTION_OPTION,
+  COMPRESS_PROGRAM_OPTION,
   DELAY_DIRECTORY_RESTORE_OPTION,
   HARD_DEREFERENCE_OPTION,
   DELETE_OPTION,
@@ -657,8 +658,15 @@ static struct argp_option options[] = {
   {"no-auto-compress", NO_AUTO_COMPRESS_OPTION, 0, 0,
    N_("do not use archive suffix to determine the compression program"),
    GRID+1 },
-  {"use-compress-program", 'I', N_("PROG"), 0,
-   N_("filter through PROG (must accept -d)"), GRID+1 },
+  {"filter-program", 'I', N_("PROG"), 0,
+   N_("filter archive through PROG (PROG must accept -d)"), GRID+1 },
+  {"use-compress-program", 0, N_("PROG"), OPTION_ALIAS | OPTION_HIDDEN, NULL,
+   GRID+1 },
+  {"compress-program", COMPRESS_PROGRAM_OPTION, N_("PROG"), 0,
+   N_("filter archive through PROG having COMPRESS-like API, this is similar "
+      "to --filter-program except that the PROG's exit value 2 means just a "
+      "warning (PROG must accept -d option)"),
+   GRID+1 },
   /* Note: docstrings for the options below are generated by tar_help_filter */
   {"bzip2", 'j', 0, 0, NULL, GRID+1 },
   {"gzip", 'z', 0, 0, NULL, GRID+1 },
@@ -1327,6 +1335,7 @@ tar_help_filter (int key, const char *text, void *input)
 
     case LZMA_OPTION:
       s = xasprintf (_("filter the archive through %s"), LZMA_PROGRAM);
+      compress_like_api = true;
       break;
 
     case 'J':
@@ -1579,6 +1588,7 @@ parse_opt (int key, char *arg, struct argp_state *state)
 
     case 'J':
       set_use_compress_program_option (XZ_PROGRAM);
+      compress_like_api = true;
       break;
 
     case 'k':
@@ -1636,6 +1646,7 @@ parse_opt (int key, char *arg, struct argp_state *state)
 
     case LZOP_OPTION:
       set_use_compress_program_option (LZOP_PROGRAM);
+      compress_like_api = true;
       break;
 
     case 'm':
@@ -1797,10 +1808,12 @@ parse_opt (int key, char *arg, struct argp_state *state)
 
     case 'z':
       set_use_compress_program_option (GZIP_PROGRAM);
+      compress_like_api = true;
       break;
 
     case 'Z':
       set_use_compress_program_option (COMPRESS_PROGRAM);
+      compress_like_api = true;
       break;
 
     case ANCHORED_OPTION:
@@ -2161,6 +2174,11 @@ parse_opt (int key, char *arg, struct argp_state *state)
       set_use_compress_program_option (arg);
       break;
 
+    case COMPRESS_PROGRAM_OPTION:
+      set_use_compress_program_option (arg);
+      compress_like_api = true;
+      break;
+
     case VOLNO_FILE_OPTION:
       volno_file_option = arg;
       break;
-- 
1.8.1.4