On Mon, 30 Jul 2018 03:25:43 -0700, Daniel Colascione wrote:

On Mon, Jul 30, 2018 at 3:04 AM, Daniel Borkmann [off-list ref] wrote:

quoted

Hmm, I don't think such UAPI as above is future-proof. In case we would want
a similar mechanism in future for other maps, we would need a whole new bpf
command or reuse BPF_SYNCHRONIZE_MAP_TO_MAP_REFERENCES as a workaround though
the underlying map may not even be a map-to-map. Additionally, we don't have
any map object at hand in the above, so we couldn't make any finer grained
decisions either. Something like below would be more suitable and leaves room
for extending this further in future.  

YAGNI.  Your proposed mechanism doesn't add anything under the current
implementation. 

FWIW in case of HW offload targeting a particular map may allow users
to avoid a potentially slow sync with all the devices on the system.

It's also not clear how a map-specific synchronization
command is supposed to work in cases where we swap multiple map
references. Do we synchronize_rcu multiple times? Why would we impose
that inefficiency just for the sake of some non-specific future
extensibility? Add some kind of batching layer? The current approach
works for the anticipated use cases.

While my preference is not to talk about map-to-maps at all in the
user API and instead spec the thing as talking about map references in
general, I'd rather have something that talks about
references-to-maps-acquired-from-maps than this interface.