From owner-freebsd-hackers  Tue Jul 13  7:37:20 1999
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Date: Tue, 13 Jul 1999 10:36:17 -0400 (EDT)
From: "Brian F. Feldman" <green@FreeBSD.org>
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To: Luigi Rizzo <luigi@iet.unipi.it>
Cc: hackers@FreeBSD.org
Subject: Re: Why 'dd' does not seek over 'char' devs (specifically raw disk
 partitions).
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On Tue, 13 Jul 1999, Luigi Rizzo wrote:

> Hi, i have a question.
> 
> Why 'dd' does not seek over 'char' devs (specifically raw disk partitions).

Not all character devices support seeking. So, we work with the LCD...
Sorry, I don't like this either. It would be better, maybe, just to fix
character devices.

> 
> My point is, when a disk develops problems, sometimes it is possible
> to recover nearby sectors e.g. using dd, and seeking to the right
> block. However running dd over the char device (rwd*) takes forever
> because the seek on char devices is implemented by reading instead.
> Using the cooked device is problematic because the buffering causes
> multiple sectors to be read and this may cause errors if some block
> nearby has problems.

You certainly make a good case. modify your local copy of dd to do 
what you want.

> 
> I notice that on output lseek _is_ used also on char devices.

And how else would you do it?

> 
> Ideas ?
> 
> 	cheers
> 	luigi
> 
> 
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 Brian Fundakowski Feldman      _ __ ___ ____  ___ ___ ___  
 green@FreeBSD.org                   _ __ ___ | _ ) __|   \ 
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