Re: [RFC PATCH 4/6] net: sockmap with sk redirect support

On 08/03/2017 09:22 PM, Tom Herbert wrote:

On Thu, Aug 3, 2017 at 4:37 PM, John Fastabend [off-list ref] wrote:

quoted

Recently we added a new map type called dev map used to forward XDP
packets between ports (6093ec2dc313). This patches introduces a
similar notion for sockets.

A sockmap allows users to add participating sockets to a map. When
sockets are added to the map enough context is stored with the
map entry to use the entry with a new helper

  bpf_sk_redirect_map(map, key, flags)

This helper (analogous to bpf_redirect_map in XDP) is given the map
and an entry in the map. When called from a sockmap program, discussed
below, the skb will be sent on the socket using skb_send_sock().

With the above we need a bpf program to call the helper from that will
then implement the send logic. The initial site implemented in this
series is the recv_sock hook. For this to work we implemented a map
attach command to add attributes to a map. In sockmap we add two
programs a parse program and a verdict program. The parse program
uses strparser to build messages and pass them to the verdict program.
The parse program usese normal strparser semantics. The verdict
program is of type SOCKET_FILTER.

The verdict program returns a verdict BPF_OK, BPF_DROP, BPF_REDIRECT.
When BPF_REDIRECT is returned, expected when bpf program uses
bpf_sk_redirect_map(), the sockmap logic will consult per cpu variables
set by the helper routine and pull the sock entry out of the sock map.
This pattern follows the existing redirect logic in cls and xdp
programs.

Hi John,

I'm a bit confused. If the verdict program bpf_mux then? I don't see
any use of BPF_OK,DROP, or REDIRECT. I assume I'm missing something.

Tom

Ah so what I coded and what I wrote don't align perfectly here. The
verdict program _is_ bpf_mux as you guessed. I should rename the code
to use bpf_verdict (or come up with a better name). Calling it bpf_mux
was a hold out from a very specific example program I wrote up.

Then BPF_OK_DROP and BPF_REDIRECT still need to be included in below.

[...]

quoted

+
+static struct smap_psock *smap_peers_get(struct smap_psock *psock,
+                                            struct sk_buff *skb)
+{
+       struct sock *sock;
+       int rc;
+
+       rc = smap_mux_func(psock, skb);
+       if (unlikely(rc < 0))
+               return NULL;
+

replacing the above 3 lines with the following should align the commit
message and code,

	   rc = smap_mux_func(psock, skb);
	   if (rc != BPF_REDIRECT)
		return NULL;

quoted

+       sock = do_sk_redirect_map();
+       if (unlikely(!sock))
+               return NULL;
+
+       return smap_psock_sk(sock);
+}
+

And then in uapi/bpf.h

enum {
	BPF_OK_DROP,
	BPF_REDIRECT,
}

Thanks,
John