On Mon, 2023-07-03 at 14:25 -0700, John Fastabend wrote:
Jörn-Thorben Hinz wrote:
BPF applications, e.g., a TCP congestion control, might benefit from precise packet timestamps. These timestamps are already available in __sk_buff and bpf_sock_ops, but could not be requested: A BPF program was not allowed to set SO_TIMESTAMPING* on a socket. This change enables BPF programs to actively request the generation of timestamps from a stream socket.
To reuse the setget_sockopt BPF prog test for bpf_{get,set}sockopt(SO_TIMESTAMPING_NEW), also implement the missing getsockopt(SO_TIMESTAMPING_NEW) in the network stack.
I reckon the way I added getsockopt(SO_TIMESTAMPING_NEW) causes an API change: For existing users that set SO_TIMESTAMPING_NEW but queried SO_TIMESTAMPING_OLD afterwards, it would now look as if no timestamping flags have been set. Is this an acceptable change? If not, I’m happy to change getsockopt() to only be strict about the newly-implemented getsockopt(SO_TIMESTAMPING_NEW), or not distinguish between SO_TIMESTAMPING_NEW and SO_TIMESTAMPING_OLD at all.
Yeah, I think it would be best if we keep the old behavior and let SO_TIMESTAMPING_OLD return timestamps for both new/old. It looks like it should be relatively easy to implement?
Alright, I guessed that would be preferred.
Yes, if there is no objection to making the added getsockopt(SO_TIMESTAMPING_NEW) this tiny bit more “strict”, it’s just a matter of modifying the if inserted in sk_getsockopt(). (And, well, in the other case I would even remove this if.)
The difference is in the struct that is returned, on 32-bit platforms. Both calls should always be allowed? See also put_cmsg_scm_timestamping64 vs put_cmsg_scm_timestamping.
For the second patch: the _OLD/_NEW was introduced to work around limitations on 32-bit platforms. This is intended to be transparent to users, by defining SO_TIMESTAMPING accordingly.
Can the new BPF code always enforce the 64-bit version, that is, only implement the _NEW variants? And perhaps just call it SO_TIMESTAMPING directly.