Re: [PATCH v3] docs/designs: re-work the xenstore migration document...

[Jürgen Groß <jgross@xxxxxxxx>]

On 27.04.20 17:06, Paul Durrant wrote:
> From: Paul Durrant <pdurrant@xxxxxxxxxx>
>
> ... to specify a separate migration stream that will also be suitable for
> live update.
>
> The original scope of the document was to support non-cooperative migration
> of guests [1] but, since then, live update of xenstored has been brought into
> scope. Thus it makes more sense to define a separate image format for
> serializing xenstore state that is suitable for both purposes.
>
> The document has been limited to specifying a new image format. The mechanism
> for acquiring the image for live update or migration is not covered as that
> is more appropriately dealt with by a patch to docs/misc/xenstore.txt. It is
> also expected that, when the first implementation of live update or migration
> making use of this specification is committed, that the document is moved from
> docs/designs into docs/specs.
>
> NOTE: It will only be necessary to save and restore state for active xenstore
>        connections, but the documentation for 'RESUME' in xenstore.txt implies
>        otherwise. That command is unused so this patch deletes it from the
>        specification.
>
> [1] See 
> https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/designs/non-cooperative-migration.md
>
> Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
> ---
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Julien Grall <julien@xxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Wei Liu <wl@xxxxxxx>
>
> v3:
>   - Address missed comments from Juergen
Not all :-(

> v2:
>   - Address comments from Juergen
> ---
...

> +### NODE_DATA
> +
> +For live update the image format will contain a `NODE_DATA` record for each
> +node in xenstore. For migration it will only contain a record for the nodes
> +relating to the domain being migrated. The `NODE_DATA` may be related to
> +a _committed_ node (globally visible in xenstored) or a _pending_ node (created
> +or modified by a transaction for which there is also a `TRANSACTION_DATA`
> +record previously present).
>   
> -The `TRANSACTION_START` operation does not allow specification of a
> -`<domid>`; it is assumed that the transaction pertains to the domain that
> -owns the shared ring over which the operation is passed. Neither does it
> -allow a `<transid>` to be specified; it is always chosen by xenstored.
> -Hence, for the tool-stack to be able to open a transaction on behalf of a
> -domain a new operation is needed:
>   
>   ```
> -START_DOMAIN_TRANSACTION    <domid>|<transid>|
> +    0       1       2       3    octet
> ++-------+-------+-------+-------+
> +| conn-id                       |
> ++-------------------------------+
> +| tx-id                         |
> ++---------------+---------------+
> +| access        | perm-count    |
> ++---------------+---------------+
> +| perm1                         |
> ++-------------------------------+
> +...
> ++-------------------------------+
> +| permN                         |
> ++---------------+---------------+
> +| path-len      | value-len     |
> ++---------------+---------------+

path-len and value-len are still after perm1...permN, which makes it
impossible to include them in a struct.

Could you please either move them before the perm array or tell me why
not?


Juergen