Date: Wed, 5 Apr 2000 23:50:04 -0700 (PDT) From: Anatoly Vorobey <mellon@pobox.com> To: freebsd-bugs@FreeBSD.org Subject: Re: bin/17619: pax cannot read all tar files created by tar. Message-ID: <200004060650.XAA25798@freefall.freebsd.org>
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The following reply was made to PR bin/17619; it has been noted by GNATS.
From: Anatoly Vorobey <mellon@pobox.com>
To: Marc Olzheim <marcolz@stack.nl>
Cc: freebsd-gnats-submit@freebsd.org
Subject: Re: bin/17619: pax cannot read all tar files created by tar.
Date: Thu, 6 Apr 2000 08:46:40 +0000
On Mon, Apr 03, 2000 at 10:20:54AM +0200, Marc Olzheim wrote:
> > Bah. So what should be done in this case (assuming something needs
> > to be done?). I can patch pax to accept one-block archives and
> > yet produce correct archives - maybe that's the way to go? Given that
> > the GNU tar maintainer had more than 8 years to think about it, he's
> > obviously emotionally attached to one-trailing-block files and won't
> > let them go ;)
>
> That seems like a good idea to me.
See the attached patch. Tested, works fine. Maybe someone shall
review/commit it?
Index: tar.c
===================================================================
RCS file: /freebsd/cvs/src/bin/pax/tar.c,v
retrieving revision 1.13
diff -u -r1.13 tar.c
--- tar.c 1999/08/27 23:14:47 1.13
+++ tar.c 2000/04/06 08:36:55
@@ -86,7 +86,7 @@
tar_endwr()
#endif
{
- return(wr_skip((off_t)(NULLCNT*BLKMULT)));
+ return(wr_skip((off_t)(NULL_PUT*BLKMULT)));
}
/*
@@ -104,7 +104,7 @@
tar_endrd()
#endif
{
- return((off_t)(NULLCNT*BLKMULT));
+ return((off_t)(NULL_PUT*BLKMULT));
}
/*
@@ -152,8 +152,14 @@
* NOT try to id a trailer during resync mode. During resync mode we
* might as well throw this block out since a valid header can NEVER be
* a block of all 0 (we must have a valid file name).
+ *
+ * A bug in GNU tar causes it to sometimes produce trailers with
+ * just one zero block. To handle this, we will put NULL_PUT
+ * blocks in our archives, but will expect NULL_EXPECT on reads.
+ * If there are actually two zero blocks, the second one will be
+ * skipped on the next next_head() call.
*/
- if (!in_resync && (++*cnt >= NULLCNT))
+ if (!in_resync && (++*cnt >= NULL_EXPECT))
return(0);
return(1);
}
Index: tar.h
===================================================================
RCS file: /freebsd/cvs/src/bin/pax/tar.h,v
retrieving revision 1.6
diff -u -r1.6 tar.h
--- tar.h 1999/08/27 23:14:47 1.6
+++ tar.h 2000/04/06 08:32:28
@@ -44,7 +44,16 @@
#define CHK_LEN 8 /* length of checksum field */
#define TNMSZ 100 /* size of name field */
#ifdef _PAX_
-#define NULLCNT 2 /* number of null blocks in trailer */
+
+/*
+ * The USTAR format requires two null blocks to trail every file, yet
+ * GNU tar will sometimes produce tar files with only one. Hence the
+ * double standard.
+ */
+
+#define NULL_PUT 2 /* num of blocks to put in trailer */
+#define NULL_EXPECT 1 /* num of blocks to expect there */
+
#define CHK_OFFSET 148 /* start of checksum field */
#define BLNKSUM 256L /* sum of checksum field using ' ' */
#endif /* _PAX_ */
--
Anatoly Vorobey,
mellon@pobox.com http://pobox.com/~mellon/
"Angels can fly because they take themselves lightly" - G.K.Chesterton
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