link: add test for UDP iter

[lmb]

Ensure that we can create a global UDP iterator.

[lmb]

@aditighag it's possible to create an iterator, but we'll have to add support for passing a netns fd. I can take a stab at that if you have code with proposed UAPI somewhere.

[aditighag]

Sorry, I missed your ping.

it's possible to create an iterator, but we'll have to add support for passing a netns fd. I can take a stab at that if you have code with proposed UAPI somewhere.

The current default behavior is for users to enter network namespaces that they wish to iterate sockets over. So if a user wishes to iterate over all host-wide sockets, they'll need to run BPF programs with targets iter/{tcp,udp} in all netns's on the host. Maybe I'm missing something, but given that the kernel doesn't support a global iterator, what's your proposal from the library as a loader agent?

[lmb]

Maybe I'm missing something, but given that the kernel doesn't support a global iterator, what's your proposal from the library as a loader agent?

Maybe I misremembered, I thought the plan was to add UAPI which allows specifiying the netns when creating the iterator, with a special value meaning "global iterator"? If that isn't in the cards we don't need to / shouldn't change the lib.

[aditighag]

The details around the UAPI extensions are still tbd. If the TCP/UDP iterators are getting loaded by the library as expected, then it's all good for now.