Re: [Qemu-devel] [PATCH v5 1/2] spapr: Add a "no HPT" encoding to HTAB migration stream

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Jun 08, 2017 at 02:28:48PM +1000, David Gibson wrote:
> On Wed, Jun 07, 2017 at 01:24:52PM +0530, Bharata B Rao wrote:
> > Add a "no HPT" encoding (using value -1) to the HTAB migration
> > stream (in the place of HPT size) when the guest doesn't allocate HPT.
> > This will help the target side to match target HPT with the source HPT
> > and thus enable successful migration.
> > 
> > Suggested-by: David Gibson <david@gibson.dropbear.id.au>
> > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> 
> As dicussed in the thread on the previous version, I still think you
> can use section_hdr == 0 as the no-HPT encoding (matching htab_shift
> == 0.

Bharata discussed this with me on IRC and pointed out I was mistaken.
It thought the overall stream header was distinct from the incremental
content, but it's not.  The zero value in the header marks this
"chunk" of data as being continuing incremental content (the "middle"
of the stream) rather than the initial stream header which gives the
HPT size.

So, yes, we do need a new and different encoding for "no HPT".

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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