Re: [Xen-devel] [PATCH v3 2/2] docs/designs: Add a design document for migration of xenstore data

[Jürgen Groß <jgross@xxxxxxxx>]

On 28.01.20 13:28, Paul Durrant wrote:
> This patch details proposes extra migration data and xenstore protocol
> extensions to support non-cooperative live migration of guests.
>
> Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
> ---
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Julien Grall <julien@xxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Wei Liu <wl@xxxxxxx>
>
> v3:
>   - New in v3
> ---
>   docs/designs/xenstore-migration.md | 122 +++++++++++++++++++++++++++++
>   1 file changed, 122 insertions(+)
>   create mode 100644 docs/designs/xenstore-migration.md
>
> diff --git a/docs/designs/xenstore-migration.md 
> b/docs/designs/xenstore-migration.md
> new file mode 100644
> index 0000000000..9020b6ff9a
> --- /dev/null
> +++ b/docs/designs/xenstore-migration.md
> @@ -0,0 +1,122 @@
> +**watch data**
> +
> +
> +`<path>|<token>|`
> +
> +`<path>` again is considered relative and, together with `<token>`, should
> +be suitable to formulate an `ADD_DOMAIN_WATCHES` operation (see below).
> +Note that `<path>` must not be a *special* value (beginning with `@`).
Why not? This is possible for a guest, so it should be possible to
migrate such a watch.

Today it might not make any sense, but we should not block any future
special values which might make sense for a guest to use.

> +
> +
> +### Protocol Extension
> +
> +The `WATCH` operation does not allow specification of a `<domid>`; it is
> +assumed that the watch pertains to the domain that owns the shared ring
> +over which the operation is passed. Hence, for the tool-stack to be able
> +to register a watch on behalf of a domain a new operation is needed:
> +
> +```
> +ADD_DOMAIN_WATCHES      <domid>|<watch>|+
> +
> +Adds watches on behalf of the specified domain.
> +
> +<watch> is a NUL separated tuple of <path>|<token>. <path> must not be
> +@<wspecial>, otherwise the semantics of this operation are identical to
> +the domain issuing WATCH <path>|<token>|.
I wouldn't exclude @<wspecial>.


Juergen

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