Date: Wed, 11 Jul 2007 08:40:09 GMT From: Bernd Luevelsmeyer <bdluevel@heitec.net> To: freebsd-bugs@FreeBSD.org Subject: Re: bin/106973: tar(1) cannot read own tape, but pax(1) can Message-ID: <200707110840.l6B8e9bY030950@freefall.freebsd.org>
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The following reply was made to PR bin/106973; it has been noted by GNATS.
From: Bernd Luevelsmeyer <bdluevel@heitec.net>
To: bug-followup@FreeBSD.org
Cc: Tim Kientzle <kientzle@freebsd.org>
Subject: Re: bin/106973: tar(1) cannot read own tape, but pax(1) can
Date: Wed, 11 Jul 2007 10:36:49 +0200
This issue came up in the freebsd-stable mailing list. Tim Kientzle
wrote in <46679117.5060909@freebsd.org> that the SCSI tape driver in 6.2
claims to be able to do lseek() while in fact it cannot. tar believes it
and issues lseek() commands, whereupon things go bad. (Apparently, pax
simply doesn't use lseek() commands, hence has no problems.)
In <4675CD95.9040004@freebsd.org>, he published a patch that prevents
tar from using lseek() commands. With this patch, tar works just fine
for me again. However, IMHO this is only a workaround; really, the tape
driver should not be lying about its capabilities.
Here is the patch:
--- archive_read_open_filename.c (revision 124)
+++ archive_read_open_filename.c (working copy)
@@ -165,6 +165,15 @@
struct read_file_data *mine = (struct read_file_data
*)client_data;
off_t old_offset, new_offset;
+ /*
+ * Workaround for broken tape interfaces that don't support
+ * seek(), but return success if you ask them to seek(). This
+ * also, of course, slows down archive scanning significantly
+ * on devices that can seek. Yuck.
+ */
+ if (S_ISCHR(mine->st_mode) || S_ISBLK(mine->st_mode))
+ return (0);
+
/* Reduce request to the next smallest multiple of block_size */
request = (request / mine->block_size) * mine->block_size;
/*
I request that the PR's class be changed to kernel (since the error is
in a driver).
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