Date: Tue, 13 Jul 1999 10:36:17 -0400 (EDT) From: "Brian F. Feldman" <green@FreeBSD.org> 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). Message-ID: <Pine.BSF.4.10.9907131034360.76301-100000@janus.syracuse.net> In-Reply-To: <199907131250.OAA00397@prova.iet.unipi.it>
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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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