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Date:      Thu, 30 Dec 2004 09:23:56 -0500
From:      ari edelkind <edelkind-freebsd-hackers@episec.com>
To:        freebsd-hackers@FreeBSD.ORG
Subject:   Re: Creating Compressed Loop FS from stdin
Message-ID:  <20041230142356.GQ3608@episec.com>
In-Reply-To: <20041230140007.GH830@straylight.m.ringlet.net>
References:  <1104358540.2895.10.camel@kaiser.sig11.org> <20041230103433.GB830@straylight.m.ringlet.net> <1104409708.6657.1.camel@kaiser.sig11.org> <20041230123116.GE830@straylight.m.ringlet.net> <41D4036B.1060600@portaone.com> <20041230140007.GH830@straylight.m.ringlet.net>

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roam@ringlet.net wrote:

> > It will not help, since AFAIK you can't seek stdin anyway, or even if I 
> > am wrong and you can seek it to the end you will be unable to seek it 
> > backward.
> 
> I tested the patch before posting it, fully expecting to find that stdin
> really cannot be seeked (sought? :), and surprisingly it worked, at least
> on RELENG_5 as of today!

You can always seek stdin, if stdin happens to be associated with a
seekable descriptor.  It isn't given any special treatment simply
because it has a vector of 0.  That is, if you use something along the
lines of:

    % ./seekme </etc/services

then /etc/services is associated with descriptor 0, and you can seek all
you like.  If you use

    % cat /etc/services |./seekme

... then the descriptor isn't associated with a file, and you'll run
into problems.

ari



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