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Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option |
Date: |
Thu, 16 Aug 2018 09:15:15 +0200 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
Am 16.08.2018 um 04:49 hat Max Reitz geschrieben:
> On 2018-08-16 04:39, Eric Blake wrote:
> > If convert were more powerful, I'd be fine dropping 'qemu-img dd' after
> > a proper deprecation period.
>
> Technically it has those features already, with the raw block driver's
> offset and size parameters.
In a way, yes. It requires you to precreate the target image, though,
because --target-image-opts requires -n.
We'll probably want to fix something in this area anyway because in the
common case, you already need those options to even precreate the image,
and qemu-img create doesn't support open options for the protocol layer
either (unlike blockdev-create).
> >> ((That gave me a good idea. Actually, it's probably not such a good
> >> idea, but I guess I'll do it in my spare time anyway. A qemu-img fuse
> >> might be nice which represents an image as a raw image at some mount
> >> point. Benefits over qemu-nbd: (1) You don't need root, (2) you don't
> >> need to type modprobe nbd.))
> >
> > So the kernel->userspace translation would be happening via the FUSE
> > interface instead of the NBD interface. Data still bounces around just
> > as much, but it might be a fun project. Does fuse behave well when
> > serving exactly one file at the mountpoint, rather than the more typical
> > file system rooted in a directory? NBD at least has the benefit of
> > claiming to be a block device all along, rather than complicating the
> > user interface with POSIX file system rules (which you'll be bending,
> > because you are serving exactly one file instead of a system).
To make it more real, you could expose a snapshots/ subdirectory. Or
maybe better not.
> Well, but I can just pretend my FUSE file is a block device, no?
>
> Also, I just discovered something really interesting: FUSE allows you to
> specify a single file as a mountpoint.
>
> And you know what? You can open the original file before you replace it
> by the FUSE "filesystem".
>
> So my fun interface is going to looks like this:
>
> $ qemu-img fuse foo.qcow2
>
> And then your foo.qcow2 is a raw image until the next "fusermount -u
> foo.qcow2"! Isn't that fun?
Yes, sounds fun. Until you realise that I'd actually like to merge
something like this when it exists. ;-)
For a more serious implementation, maybe it should even be a separate
qemu-fuse rather than a qemu-img subcommand.
Kevin
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- [Qemu-devel] [PATCH 1/2] qemu-img: Fix dd with skip= and count=, (continued)
[Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Eric Blake, 2018/08/14
- Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Max Reitz, 2018/08/15
- Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Eric Blake, 2018/08/15
- Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Eric Blake, 2018/08/15
- Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Max Reitz, 2018/08/15
- Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Eric Blake, 2018/08/15
- Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Max Reitz, 2018/08/15
- Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option,
Kevin Wolf <=
- Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Max Reitz, 2018/08/17
Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Fam Zheng, 2018/08/19
Re: [Qemu-devel] [PATCH 2/2] qemu-img: Add dd seek= option, Max Reitz, 2018/08/20
Re: [Qemu-devel] [PATCH 0/2] Improve qemu-img dd, Eric Blake, 2018/08/15
Re: [Qemu-devel] [PATCH 0/2] Improve qemu-img dd, no-reply, 2018/08/16
Re: [Qemu-devel] [PATCH 0/2] Improve qemu-img dd, no-reply, 2018/08/16
Re: [Qemu-devel] [PATCH 0/2] Improve qemu-img dd, Eric Blake, 2018/08/19