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Preserving transactions accross Xenstored Live-Update

Hi Juergen,

I have started to look at preserving transaction accross Live-update in C Xenstored. So far, I managed to transfer transaction that read/write existing nodes.

Now, I am running into trouble to transfer new/deleted node within a transaction with the existing migration format.

C Xenstored will keep track of nodes accessed during the transaction but not the children (AFAICT for performance reason).

Therefore we have the name of the children but not the content (i.e. permission, data...).

I have been exploring a couple of approaches:
   1) Introducing a flag to indicate there is a child but no content.

  * Close to the existing stream.
  * Fairly implementation agnostic.

* Memory overhead as we need to transfer the full path (rather than the child name) * Checking for duplication (if the node was actually accessed) will introduce runtime overhead.

2) Extend XS_STATE_TYPE_NODE (or introduce a new record) to allow transferring the children name for transaction

  * The implementation is more straight forward

   * The stream becomes implementation specific

Neither approach looks very appealing to me. So I would like to request some feedback for other proposals or preference between the two options.

Note that I haven't looked into much detail how transactions works on OCaml Xenstored.


Julien Grall



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