Re: [Xen-devel] [PATCH for-4.9 4/4] docs: Clarify the expected behaviour of zero-content records

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.03.17 at 18:32, <andrew.cooper3@xxxxxxxxxx> wrote:
> @@ -631,6 +631,11 @@ The set of valid records depends on the guest 
> architecture and type.  No
>  assumptions should be made about the ordering or interleaving of
>  independent records.  Record dependencies are noted below.
>  
> +Some records are used for signalling, and explicitly have zero length.  All
> +other records contain data relevent to the migration.  Data records with no

relevant?

> +content should be elided on the source side, as they their presence serves no

Stray "they"?

> +purpose, but result in extra work for the restore side.

results?

> @@ -719,3 +724,12 @@ restored.
>  The image header may only be extended by _appending_ additional
>  fields.  In particular, the `marker`, `id` and `version` fields must
>  never change size or location.
> +
> +
> +Errata
> +======
> +
> +1. For compatibility with older code, the receving side of a stream should
> +   tolerate and ignore variable sized records with zero content.  Xen 
> releases
> +   between 4.6 and 4.8 could end up generating valid HVM\_PARAMS or
> +   X86\_PV\_VCPU\_{EXTENDED,XSAVE,MSRS} records with 0 content.

Also elsewhere in the series you use expressions similar to this "0
content", but especially here (with no code next to it) it is rather
ambiguous: Do you mean zero-length content, or non-zero-length
content being all zero, or both?

Jan


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