Date: 30 Apr 1999 00:01:11 +0200 From: naddy@mips.rhein-neckar.de (Christian Weisgerber) To: freebsd-stable@freebsd.org Subject: Re: Does tar do sparse files these days Message-ID: <7gakr7$ep0$1@mips.rhein-neckar.de> References: <7g7vdc$3e6$1@mips.rhein-neckar.de> <199904291758.NAA25146@po1.bbn.com>
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Dennis Rockwell <dennis@bbn.com> wrote:
> You would have to do run-length encoding of all strings of
> nulls above some small threshhold, regardless of their
> alignment, then always seek over these strings when
> retrieving.
Right.
> Since, as you say, the API doesn't reflect these holes, manufacturing
> new holes isn't a problem, and even saves some disk space.
I'm under the impression that holes are a bad idea in a swap file. But
since you need to apply the above heuristic only if stat.st_blocks
suggests holes in the first place, this is likely not a problem. Beware
of making holes unconditionally, though.
> I don't know if the file format would support this, and I
> wouldn't expect something this CPU-expensive to be the
> default behavior.
As I mentioned previously, you can enable this with "-S" for GNU tar.
The POSIX ustar format doesn't support it, so all tar's that offer such
an option implement it by way of some format extension.
--
Christian "naddy" Weisgerber naddy@mips.rhein-neckar.de
100+ SF Book Reviews: <URL:http://home.pages.de/~naddy/reviews/>;
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