Re: [Xen-devel] [PATCH 3/4] tools/libxc: Avoid generating inappropriate zero-length records

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Jul 21, 2016 at 06:17:36PM +0100, Andrew Cooper wrote:
> It was never intended for records such as these to be sent with zero content.
> 

Wouldn't it be better to modify write_split_record to ignore zero
content instead of patching up different places?

> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  tools/libxc/xc_sr_save_x86_hvm.c |  4 ++++
>  tools/libxc/xc_sr_save_x86_pv.c  | 12 ++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/tools/libxc/xc_sr_save_x86_hvm.c 
> b/tools/libxc/xc_sr_save_x86_hvm.c
> index ba50a43..5401bf9 100644
> --- a/tools/libxc/xc_sr_save_x86_hvm.c
> +++ b/tools/libxc/xc_sr_save_x86_hvm.c
> @@ -112,6 +112,10 @@ static int write_hvm_params(struct xc_sr_context *ctx)
>          }
>      }
>  
> +    /* No params? Skip this record. */
> +    if ( hdr.count == 0 )
> +        return 0;
> +
>      rc = write_split_record(ctx, &rec, entries, hdr.count * 
> sizeof(*entries));
>      if ( rc )
>          PERROR("Failed to write HVM_PARAMS record");
> diff --git a/tools/libxc/xc_sr_save_x86_pv.c b/tools/libxc/xc_sr_save_x86_pv.c
> index 4a29460..5fb9f2f 100644
> --- a/tools/libxc/xc_sr_save_x86_pv.c
> +++ b/tools/libxc/xc_sr_save_x86_pv.c
> @@ -607,6 +607,10 @@ static int write_one_vcpu_extended(struct xc_sr_context 
> *ctx, uint32_t id)
>          return -1;
>      }
>  
> +    /* No content? Skip the record. */
> +    if ( domctl.u.ext_vcpucontext.size == 0 )
> +        return 0;
> +
>      return write_split_record(ctx, &rec, &domctl.u.ext_vcpucontext,
>                                domctl.u.ext_vcpucontext.size);
>  }
> @@ -662,6 +666,10 @@ static int write_one_vcpu_xsave(struct xc_sr_context 
> *ctx, uint32_t id)
>          goto err;
>      }
>  
> +    /* No xsave state? Skip this record. */
> +    if ( domctl.u.vcpuextstate.size == 0 )
> +        goto out;
> +
>      rc = write_split_record(ctx, &rec, buffer, domctl.u.vcpuextstate.size);
>      if ( rc )
>          goto err;
> @@ -728,6 +736,10 @@ static int write_one_vcpu_msrs(struct xc_sr_context 
> *ctx, uint32_t id)
>          goto err;
>      }
>  
> +    /* No MSRs? Skip this record. */
> +    if ( domctl.u.vcpu_msrs.msr_count == 0 )
> +        goto out;
> +
>      rc = write_split_record(ctx, &rec, buffer,
>                              domctl.u.vcpu_msrs.msr_count *
>                              sizeof(xen_domctl_vcpu_msr_t));
> -- 
> 2.1.4
> 

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