Re: [Xen-devel] [PATCH v3 3/6] libxc/migration: Specification update for CHECKPOINT records

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 12/05/15 10:35, Andrew Cooper wrote:
> Checkpointed streams need to signal the end of a consistent view of VM state,
> and the start of the libxl data.
[...]
> --- a/docs/specs/libxc-migration-stream.pandoc
> +++ b/docs/specs/libxc-migration-stream.pandoc
[...]
> @@ -578,6 +578,23 @@ The verify record contains no fields; its body_length is 
> 0.
>  
>  \clearpage
>  
> +CHECKPOINT
> +----------
> +
> +A checkpoint record indicates that the records thusfar in the stream 
> represent

...that all the preceding records in the stream represent...

> +a consistent view of VM state.

> +
> +     0     1     2     3     4     5     6     7 octet
> +    +-------------------------------------------------+
> +
> +The checkpoint record contains no fields; its body_length is 0
> +
> +A stream containing checkpoint records must have indicated itself as a
> +checkpointed stream in the Image Header.  Conversely, a stream not identified
> +as checkpointed must not contain checkpoint records.

This paragraph is stale.

I think you should expand a bit more on this record.  Perhaps:

  If the stream is embedded in a higher level toolstack stream, the
  CHECKPOINT record marks the end of the libxc portion of the stream
  and the stream is handed back to the higher level for further
  processing.

  The higher level stream may then hand the stream back to libxc to
  process another set of records for the next consistent VM state
  snapshot.  This next set of records may be terminated by another
  CHECKPOINT record or an END record.

David

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