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

[Laurent Vivier <lvivier@redhat.com>]

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()).

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);
     }

Laurent