Date: Tue, 13 Jul 1999 15:02:38 -0400 (EDT) From: "Brian F. Feldman" <green@FreeBSD.org> To: John Polstra <jdp@polstra.com> Cc: hackers@FreeBSD.org Subject: Re: Why 'dd' does not seek over 'char' devs (specifically raw disk Message-ID: <Pine.BSF.4.10.9907131501270.86113-100000@janus.syracuse.net> In-Reply-To: <199907131646.JAA36852@vashon.polstra.com>
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On Tue, 13 Jul 1999, John Polstra wrote: > In article <Pine.BSF.4.10.9907131042310.76301-100000@janus.syracuse.net>, > Brian F. Feldman <green@FreeBSD.ORG> wrote: > > On Tue, 13 Jul 1999, Luigi Rizzo wrote: > > > > > couldn't we first try lseek and only do the reads on char devs where > > > the lseek fails ? > > > > lseek() won't usually fail unless it's something like EBADF. It merely > > sets the current fd's offset. It would be nice to be able to tell from > > a device driver if it supports seeking (da) or not (sa). Hmm... actually, > > if we just specify somehow that we support either direct or sequential > > access... this would be possible. > > It would be a big improvement if dd could handle seeking on character > disk devices. I'm reasonably certain there exists some ioctl (perhaps > related to reading disk labels) which could be used to figure out > whether a character device was a disk or not. A simple fix like that > would make dd a lot more useful for the case Luigi brought up. Okay, I implemented it, and it's in -CURRENT. I forgot about dsioctl()... I was thinking in majors and minors, and that they'd have to be hardcoded in... ;) This is better. > > John > -- > John Polstra jdp@polstra.com > John D. Polstra & Co., Inc. Seattle, Washington USA > "No matter how cynical I get, I just can't keep up." -- Nora Ephron > Brian Fundakowski Feldman _ __ ___ ____ ___ ___ ___ green@FreeBSD.org _ __ ___ | _ ) __| \ FreeBSD: The Power to Serve! _ __ | _ \._ \ |) | http://www.FreeBSD.org/ _ |___/___/___/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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