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Re: [Qemu-block] [Qemu-devel] [PATCH v1 3/6] qemu-img: add support for -

From: Daniel P. Berrange
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v1 3/6] qemu-img: add support for -n arg to dd command
Date: Mon, 6 Feb 2017 10:31:04 +0000
User-agent: Mutt/1.7.1 (2016-10-04)

On Fri, Feb 03, 2017 at 07:56:11PM +0100, Max Reitz wrote:
> > In case you say that's inconvenient: pretty much everything about dd's
> > archaic user interface is inconvenient.  If you want convenient, roll
> > your own.  If you want familiar, stick to the original.
> I agree. But qemu-img dd already is not dd. It interprets disk image
> files as virtual disks instead of as plain files. The question is
> whether virtual disks are to be treated as block devices or as files.
> I don't have a strong opinion on the matter. Either way will surprise
> some people. The original issue was whether to make nocreat/notrunc a
> mandatory option, so if we didn't have any backwards compatibility
> issues, it would be the following two surprises:
> (1) Don't make nocreat/notrunc mandatory (as it is now). Then people
>     who expect qemu-img dd to treat image files as block devices will
>     be surprised that all their data is gone. Bad.

I don't think people really expect qemu-img to treat image file as if
they were block devices when operating on the host.

It is like saying people expect /usr/bin/dd to treat a plain file
as a block device, because they might use it with losetup later.

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