On Mon, Mar 29, 2021 at 8:03 AM John Fastabend [off-list ref] wrote:

Alexei Starovoitov wrote:

quoted

On Sun, Mar 28, 2021 at 01:20:00PM -0700, Cong Wang wrote:

quoted

From: Cong Wang <redacted>

We have thousands of services connected to a daemon on every host
via AF_UNIX dgram sockets, after they are moved into VM, we have to
add a proxy to forward these communications from VM to host, because
rewriting thousands of them is not practical. This proxy uses an
AF_UNIX socket connected to services and a UDP socket to connect to
the host. It is inefficient because data is copied between kernel
space and user space twice, and we can not use splice() which only
supports TCP. Therefore, we want to use sockmap to do the splicing
without going to user-space at all (after the initial setup).

Currently sockmap only fully supports TCP, UDP is partially supported
as it is only allowed to add into sockmap. This patchset, as the second
part of the original large patchset, extends sockmap with:
1) cross-protocol support with BPF_SK_SKB_VERDICT; 2) full UDP support.

On the high level, ->read_sock() is required for each protocol to support
sockmap redirection, and in order to do sock proto update, a new ops
->psock_update_sk_prot() is introduced, which is also required. And the
BPF ->recvmsg() is also needed to replace the original ->recvmsg() to
retrieve skmsg. To make life easier, we have to get rid of lock_sock()
in sk_psock_handle_skb(), otherwise we would have to implement
->sendmsg_locked() on top of ->sendmsg(), which is ugly.

Please see each patch for more details.

To see the big picture, the original patchset is available here:
https://github.com/congwang/linux/tree/sockmap
this patchset is also available:
https://github.com/congwang/linux/tree/sockmap2

---
v7: use work_mutex to protect psock->work
    return err in udp_read_sock()
    add patch 6/13
    clean up test case

The feature looks great to me.
I think the selftest is a bit light in terms of coverage, but it's acceptable.

+1

Well, the first half of this patchset still focuses on the existing code, which
is already covered by existing test cases. The second half adds
BPF_SK_SKB_VERDICT and UDP support, which are already covered by
my new test case. And apparently UDP will never support other sockmap
programs like TCP, for example, BPF_SK_SKB_STREAM_PARSER, hence
it of course has much less test cases than TCP. Cross-protocol test case
will be added in the next patchset when AF_UNIX comes in.

If I miss anything, please be specific. Just saying the test case is light does
not help me to understand what I need to add.

Thanks.