Re: [Xen-devel] [PATCH] libxc: really tolerate empty PV records

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 27/02/18 14:51, Jan Beulich wrote:
> Commit 119ee4d773 ("tools/libxc: Tolerate specific zero-content records
> in migration v2 streams") meant tolerate those, but failed to set rc
> accordingly.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

> ---
> This is what is currently breaking save/restore on the 4.8 branch; I
> haven't checked yet why the sending side produces an empty record there.
> I wonder whether that's related to f1a0a8c3fe ("tools/libxc: Fix
> restoration of PV MSRs after migrate") not having been backported yet.
> Otoh the latter is missing on 4.7 too, yet there save/restore doesn't
> fail.

It will be 72efb1df6 "Avoid generating inappropriate zero-content
records" which is missing.

It triggers when there are a non-zero maximum number of MSRs, but zero
MSRs to tend after Xen skips the empty MSRs.

~Andrew

>
> --- a/tools/libxc/xc_sr_restore_x86_pv.c
> +++ b/tools/libxc/xc_sr_restore_x86_pv.c
> @@ -770,6 +770,7 @@ static int handle_x86_pv_vcpu_blob(struc
>      {
>          DBGPRINTF("Skipping empty %s record for vcpu %u\n",
>                    rec_type_to_str(rec->type), vhdr->vcpu_id);
> +        rc = 0;
>          goto out;
>      }
>  
>
>
>


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