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

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

[1] See 

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>

  - Address missed comments from Juergen

Not all :-(

  - Address comments from Juergen


+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




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