Re: [Qemu-devel] [patch 3/4] block stream: add support for partial streaming

[Marcelo Tosatti]

On Wed, Jan 04, 2012 at 09:02:06AM -0700, Eric Blake wrote:
> On 01/04/2012 07:08 AM, Marcelo Tosatti wrote:
> > Add support for streaming data from an intermediate section of the 
> > image chain (see patch and documentation for details).
> > 
> > Signed-off-by: Marcelo Tosatti <address@hidden>
> > 
> > Index: stefanha/block.c
> > ===================================================================
> > --- stefanha.orig/block.c
> > +++ stefanha/block.c
> > @@ -2229,6 +2229,70 @@ int bdrv_is_allocated(BlockDriverState *
> >      return data.ret;
> >  }
> >  
> > +/*
> > + * Given an image chain: [BASE] -> [INTER1] -> [INTER2] -> [TOP]
> > + *
> > + * Return true if the given sector is allocated in top or base.
> > + * Return false if the given sector is allocated in intermediate images.
> > + *
> > + * 'pnum' is set to the number of sectors (including and immediately 
> > following
> > + *  the specified sector) that are known to be in the same
> > + *  allocated/unallocated state.
> 
> Not a problem with this patch, per say, so much as a question about the
> next steps:
> 
> How hard would it be to go one step further, and provide a monitor
> command where qemu could dump the state of BASE, INTER1, or INTER2
> without removing it from the image chain?  Libvirt would really like to
> be able to have a command where the user can request to inspect to see
> the contents of (a portion of) the disk at the time the snapshot was
> created, all while qemu continues to run and the TOP file continues to
> be adding deltas to that portion of the disk.

What exactly do you mean "dump the state of"? You want access to
the contents of INTER2, INTER1, BASE, via libguestfs?

> For that matter, I'm still missing out on the ability to extract the
> contents of a qcow2 internal snapshot from an image that is in use by
> qemu - we have the ability to delete internal snapshots but not to probe
> their contents.

Same question (although i am not familiar with internal snapshots).