[Bug-tar] [Fwd: Bug#543913: "tar tf" uses read() instead of lseek(), making it slow]

[Bdale Garbee]

A user of our Debian packages of tar points out that it might be more
efficient to use lseek() in some circumstances, particularly for
archives containing a small number of large files.

Bdale

> --- Begin Message ---
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> Subject: 
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> Bug#543913: "tar tf" uses read() instead of lseek(), making it slow
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> Date: 
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> Thu, 27 Aug 2009 14:09:35 +0200
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> Package: tar
> Version: 1.20-1
> Severity: normal
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> When running "tar tf" on a large tarball containing few large files, tar
> becomes incredibly slow. The reason for this is that tar issues many
> read()s to skip the file content, but as it doesn't need the content, it
> throws it away. GNU tar could just use lseek() like libarchive and busybox
> do.
>
> Also a problem is extracting only one file from said tarball, where the
> other files do not need to be read for just that one to be extracted.
>
> The problem exists on all versions of GNU tar and was confirmed to exist
> on at least all versions starting from etchthe one shipped with Etch.
>
> -- System Information:
> Debian Release: 5.0.2
>   APT prefers testing
>   APT policy: (500, 'testing')
> Architecture: amd64 (x86_64)
>
> Kernel: Linux 2.6.26-2-amd64 (SMP w/1 CPU core)
> Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
> Shell: /bin/sh linked to /bin/dash
>
> Versions of packages tar depends on:
> ii  libc6                         2.9-12     GNU C Library: Shared libraries
>
> tar recommends no packages.
>
> Versions of packages tar suggests:
> ii  bzip2                         1.0.5-2    high-quality block-sorting file co
> pn  ncompress                     <none>     (no description available)
>
> -- no debconf information
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> --- End Message ---