[Qemu-devel] Base images

[Qemu-devel] Base images

[David Roberts]

Hi,

I've got a couple of questions about creating images linked to base images:
- `qemu-img commit` commits changes directly to the base image. Is there a way 
to create a new merged image with the changes so as not to change the 
original?
- I noticed that images refer to their base image using an absolute path. Is 
there a way to change an image's base image reference? (for example when the 
base image is renamed / moved to a different directory)

-- 
David Roberts :)
http://kavenc.sf.net/

Re: [Qemu-devel] Base images

[Michael McConnell]

David Roberts wrote:
> Hi,
> 
> I've got a couple of questions about creating images linked to base images:
> - `qemu-img commit` commits changes directly to the base image. Is there a way 
> to create a new merged image with the changes so as not to change the 
> original?
> - I noticed that images refer to their base image using an absolute path. Is 
> there a way to change an image's base image reference? (for example when the 
> base image is renamed / moved to a different directory)

qemu-img convert [-c] <changes-file> -O qcow <new-base-file>

should do what you want.

-- 
-- Michael "Soruk" McConnell
   Eridani Star System

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Re: [Qemu-devel] Base images

[Eric Hameleers]

David Roberts wrote:

> Hi,
> 
> I've got a couple of questions about creating images linked to base images:
> - `qemu-img commit` commits changes directly to the base image. Is there a way
> to create a new merged image with the changes so as not to change the
> original?
> - I noticed that images refer to their base image using an absolute path. Is
> there a way to change an image's base image reference? (for example when the
> base image is renamed / moved to a different directory)

Would be nice if a command like:
  "qemu-img relocate <filename> -p <path_to_new_base_image>"
would be added.
I have been able sometimes to hack new path names into the header of
the qemu image-file but that is not an ideal solution, and it is not
always possible.

Eric

-- 
Eric Hameleers
RedHat Certified Engineer #808003505607683
Linux Knowledge Center, IBM Global Services

Re: [Qemu-devel] Base images

[David Roberts]

> Would be nice if a command like:
>   "qemu-img relocate <filename> -p <path_to_new_base_image>"
> would be added.
Yes, thats the kind of thing I was hoping for.

> I have been able sometimes to hack new path names into the header of
> the qemu image-file but that is not an ideal solution, and it is not
> always possible.
Does sed work, or will it just corrupt the image?

-- 
David Roberts :)
http://kavenc.sf.net/

Re: [Qemu-devel] Base images

[David Roberts]

> qemu-img convert [-c] <changes-file> -O qcow <new-base-file>
>
> should do what you want.
Great. However, does that mean that I cannot compress an image without merging 
it with its base image?

-- 
David Roberts :)
http://kavenc.sf.net/

Re: [Qemu-devel] Base images

[Michael McConnell]

On Wed, 22 Nov 2006, David Roberts wrote:

> > qemu-img convert [-c] <changes-file> -O qcow <new-base-file>
> >
> > should do what you want.
> Great. However, does that mean that I cannot compress an image without merging 
> it with its base image?

I believe so, yes. It makes sense for the changes file to be uncompressed, 
since it makes life so much simpler (and faster) for random-access writes.

-- Michael "Soruk" McConnell
   Eridani Star System

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Re: [Qemu-devel] Base images

[Don Kitchen]

Re: [Qemu-devel] Base images

[Don Kitchen]

> > - I noticed that images refer to their base image using an absolute path. Is
> > there a way to change an image's base image reference? (for example when the
> > base image is renamed / moved to a different directory)
> qemu-img convert [-c] <changes-file> -O qcow <new-base-file>
> should do what you want.

I believe that forces a delta file to merge in with its base. Definately not the same as relocation.

Example:
delta1.img and delta2.img are both based on /root/base1.img. The directory's
getting crowded, so you want to move base1.img into /root/qemu/base1.img.
But once you do that, delta1 and delta2 can't find it. So how is it possible
to have a relocated base1.img without merging either delta1 or delta2, which
are mutually exclusive?

Thanks

Re: [Qemu-devel] Base images

[Michael McConnell]

On Thu, 23 Nov 2006, Don Kitchen wrote:

> > > - I noticed that images refer to their base image using an absolute path. Is
> > > there a way to change an image's base image reference? (for example when the
> > > base image is renamed / moved to a different directory)
> > qemu-img convert [-c] <changes-file> -O qcow <new-base-file>
> > should do what you want.
> 
> I believe that forces a delta file to merge in with its base. Definately not the same as relocation.

The original question I answered:

David Roberts wrote:
> Hi,
> 
> I've got a couple of questions about creating images linked to base images:
> - `qemu-img commit` commits changes directly to the base image. Is there a
> way to create a new merged image with the changes so as not to change the
> original?

...and my qemu-img convert command above will do exactly that.

Your misquoting has implied the command I gave would do something else, which 
it won't.

-- Michael "Soruk" McConnell
   Eridani Star System

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