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Re: [Qemu-block] [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option

From: Max Reitz
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option
Date: Mon, 20 Aug 2018 14:20:20 +0200
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On 2018-08-20 04:07, Fam Zheng wrote:
> On Thu, 08/16 04:20, Max Reitz wrote:
>> No, the real issue is that dd is still not implemented just as a
>> frontend to convert.  Which it should be.  I'm not sure dd was a very
>> good idea from the start, and now it should ideally be a frontend to
>> convert.
>> (My full opinion on the matter: dd has a horrible interface.  I don't
>> quite see why we replicated that inside qemu-img.  Also, if you want to
>> use dd, why not use qemu-nbd + Linux nbd device + real dd?)
> The intention is that dd is a familiar interface and allows for operating on
> portions of images. It is much more convenient than "qemu-nbd + Linux nbd + 
> dd"
> and a bit more convenient than "booting a Linux VM, attaching the image as a
> virtual disk, then use dd in the guest". More so when writing tests.

This is my fault, but frankly, since I always get seek and skip mixed
up, whenever I use dd for anything but copying a whole image, I have to
look into the man page anyway, so the advantage over modprobe nbd &&
qemu-nbd -c /dev/nbd0 is gone.

And in my opinion the fact that it is a familiar interface doesn't make
it less of a horrible interface.

My main issue is that it's built right into qemu-img where it shouldn't
be.  We have convert, you can now even access portions of images with
the raw driver, so it really should have been just a script on top.


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