On Wed, May 14, 2014 at 5:05 PM, Simon Horman <[email protected]> wrote: > The sample action is rather generic, allowing arbitrary actions to be > executed based on a probability. However its use, within the Open vSwitch > code-base is limited: only a single user-space action is ever nested. > > A consequence of the current implementation of sample actions is that > depending on weather the sample action executed (due to its probability) > any side-effects of nested actions may or may not be present before > executing subsequent actions. This has the potential to complicate > verification of valid actions by the (kernel) datapath. And indeed adding > support for push and pop MPLS actions inside sample actions is one case > where such case. > > In order to allow all supported actions to be continue to be nested inside > sample actions without the potential need for complex verification code > this patch changes the implementation of the sample action in the kernel > datapath so that sample actions are more like a function call and any side > effects of nested actions are not present when executing subsequent > actions. > > With the above in mind the motivation for this change is twofold: > > * To contain side-effects the sample action in the hope of making it > easier to deal with in the future and; > * To avoid some rather complex verification code introduced in the MPLS > datapath patch. > > Some notes about the implementation: > > * This patch silently changes the behaviour of sample actions whose nested > actions have side-effects. There are no known users of such sample > actions. > > * sample() does not clone the skb for the only known use-case of the sample > action: a single nested userspace action. In such a case a clone is not > needed as the userspace action has no side effects. > > Given that there are no known users of other nested actions and in order > to avoid the complexity of predicting if other sequences of actions have > side-effects in such cases the skb is cloned. > > * As sample() provides a cloned skb in the unlikely case where there are > nested actions other than a single userspace action it is no longer > necessary to clone the skb in do_execute_actions() when executing a > recirculation action just because the keep_skb parameter is set: this > parameter was only set when processing the nested actions of a sample > action. Moreover it is possible to remove the keep_skb parameter of > do_execute_actions entirely. > > * As sample() provides either a cloned skb or one that has had a > reference taken (using keep_skb) to do_execute_actions() > the original skb passed to sample() is never consumed. Thus the > caller of sample() (also do_execute_actions()) can use its generic > error handling to free the skb on error.
This looks good to me but can you provide a signed-off-by line? _______________________________________________ dev mailing list [email protected] http://openvswitch.org/mailman/listinfo/dev
