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Firing watches on the nodes that still exist is relatively easy; just walk the tree and look at the nodes with refcount of one. Firing watches on *deleted* nodes is more fun. We add 'modified_in_tx' and 'deleted_in_tx' flags to each node. Nodes with those flags cannot be shared, as they will always be unique to the transaction in which they were created. When xs_node_walk would need to *create* a node as scaffolding and it encounters a deleted_in_tx node, it can resurrect it simply by clearing its deleted_in_tx flag. If that node originally had any *data*, they're gone, and the modified_in_tx flag will have been set when it was first deleted. We then attempt to send appropriate watches when the transaction is committed, properly delete the deleted_in_tx nodes, and remove the modified_in_tx flag from the others. Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Reviewed-by: Paul Durrant <paul@xen.org>