Re: [Qemu-devel] [Qemu-ppc] [PULL 06/21] spapr: Add a "no HPT" encoding to HTAB migration stream

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

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On Mon, Jul 17, 2017 at 09:54:45PM +0200, Laurent Vivier wrote:
> On 30/06/2017 12:46, David Gibson wrote:
> > From: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > 
> > 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>
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  hw/ppc/spapr.c | 29 +++++++++++++++++++++++++----
> >  1 file changed, 25 insertions(+), 4 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 52f4e72..f3e0b9b 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -1560,13 +1560,19 @@ static int htab_save_setup(QEMUFile *f, void *opaque)
> >      sPAPRMachineState *spapr = opaque;
> >  
> >      /* "Iteration" header */
> > -    qemu_put_be32(f, spapr->htab_shift);
> > +    if (!spapr->htab_shift) {
> > +        qemu_put_be32(f, -1);
> > +    } else {
> > +        qemu_put_be32(f, spapr->htab_shift);
> > +    }
> >  
> >      if (spapr->htab) {
> >          spapr->htab_save_index = 0;
> >          spapr->htab_first_pass = true;
> >      } else {
> > -        assert(kvm_enabled());
> > +        if (spapr->htab_shift) {
> > +            assert(kvm_enabled());
> > +        }
> >      }
> >  
> >  
> > @@ -1712,7 +1718,12 @@ static int htab_save_iterate(QEMUFile *f, void *opaque)
> >      int rc = 0;
> >  
> >      /* Iteration header */
> > -    qemu_put_be32(f, 0);
> > +    if (!spapr->htab_shift) {
> > +        qemu_put_be32(f, -1);
> > +        return 0;
> > +    } else {
> > +        qemu_put_be32(f, 0);
> > +    }
> >  
> >      if (!spapr->htab) {
> >          assert(kvm_enabled());
> > @@ -1746,7 +1757,12 @@ static int htab_save_complete(QEMUFile *f, void *opaque)
> >      int fd;
> >  
> >      /* Iteration header */
> > -    qemu_put_be32(f, 0);
> > +    if (!spapr->htab_shift) {
> > +        qemu_put_be32(f, -1);
> > +        return 0;
> > +    } else {
> > +        qemu_put_be32(f, 0);
> > +    }
> >  
> >      if (!spapr->htab) {
> >          int rc;
> > @@ -1790,6 +1806,11 @@ static int htab_load(QEMUFile *f, void *opaque, int version_id)
> >  
> >      section_hdr = qemu_get_be32(f);
> >  
> > +    if (section_hdr == -1) {
> > +        spapr_free_hpt(spapr);
> > +        return 0;
> > +    }
> > +
> >      if (section_hdr) {
> >          Error *local_err = NULL;
> >  
> > 
> 
> It seems there is a bug in this patch: when using from QEMU console the
> command "savevm", it never stops and the qcow2 image grows without limit.
> 
> I think this is because htab_save_iterate() and htab_save_complete()
> should mark the end of the sequence (the empty one, -1) by returning 1
> and not 0 (see kvmppc_save_htab()).

Ah, yes, I think you're right.  The end condition is one of the subtle
differences between the savevm and migration paths.

> This fixes the problem for me:
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 970093e..fa01511 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1827,7 +1827,7 @@ static int htab_save_iterate(QEMUFile *f, void
> *opaque)
>      /* Iteration header */
>      if (!spapr->htab_shift) {
>          qemu_put_be32(f, -1);
> -        return 0;
> +        return 1;
>      } else {
>          qemu_put_be32(f, 0);
>      }
> @@ -1866,7 +1866,7 @@ static int htab_save_complete(QEMUFile *f, void
> *opaque)
>      /* Iteration header */
>      if (!spapr->htab_shift) {
>          qemu_put_be32(f, -1);
> -        return 0;
> +        return 1;
>      } else {
>          qemu_put_be32(f, 0);
>      }

Can you polish this up and submit for merge, please?

-- 
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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