Re: [PATCH v4 bpf-next 11/11] bpf: Test BPF_SK_REUSEPORT_SELECT_OR_MIGRATE.

[Kuniyuki Iwashima]

From:   Martin KaFai Lau <kafai@xxxxxx>
Date:   Tue, 4 May 2021 22:14:08 -0700
> On Tue, Apr 27, 2021 at 12:46:23PM +0900, Kuniyuki Iwashima wrote:
> [ ... ]
> 
> > diff --git a/tools/testing/selftests/bpf/progs/test_migrate_reuseport.c b/tools/testing/selftests/bpf/progs/test_migrate_reuseport.c
> > new file mode 100644
> > index 000000000000..d7136dc29fa2
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/test_migrate_reuseport.c
> > @@ -0,0 +1,51 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Check if we can migrate child sockets.
> > + *
> > + *   1. If reuse_md->migrating_sk is NULL (SYN packet),
> > + *        return SK_PASS without selecting a listener.
> > + *   2. If reuse_md->migrating_sk is not NULL (socket migration),
> > + *        select a listener (reuseport_map[migrate_map[cookie]])
> > + *
> > + * Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx>
> > + */
> > +
> > +#include <stddef.h>
> > +#include <linux/bpf.h>
> > +#include <bpf/bpf_helpers.h>
> > +
> > +struct {
> > +	__uint(type, BPF_MAP_TYPE_REUSEPORT_SOCKARRAY);
> > +	__uint(max_entries, 256);
> > +	__type(key, int);
> > +	__type(value, __u64);
> > +} reuseport_map SEC(".maps");
> > +
> > +struct {
> > +	__uint(type, BPF_MAP_TYPE_HASH);
> > +	__uint(max_entries, 256);
> > +	__type(key, __u64);
> > +	__type(value, int);
> > +} migrate_map SEC(".maps");
> > +
> > +SEC("sk_reuseport/migrate")
> > +int prog_migrate_reuseport(struct sk_reuseport_md *reuse_md)
> > +{
> > +	int *key, flags = 0;
> > +	__u64 cookie;
> > +
> > +	if (!reuse_md->migrating_sk)
> > +		return SK_PASS;
> > +
> 
> It will be useful to check if it is migrating a child sk or
> a reqsk by testing the migrating_sk->state for TCP_ESTABLISHED
> and TCP_NEW_SYN_RECV.  skb can be further tested to check if it is
> selecting for the final ACK.  Global variables can then be
> incremented and the user prog can check that, for example,
> it is indeed testing the TCP_NEW_SYN_RECV code path...etc.
> 
> It will also become a good example for others on how migrating_sk
> can be used.

Exactly, I'll count in which state/path the migration happens and validate
them in userspace.

Thank you.


> 
> 
> > +	cookie = bpf_get_socket_cookie(reuse_md->sk);
> > +
> > +	key = bpf_map_lookup_elem(&migrate_map, &cookie);
> > +	if (!key)
> > +		return SK_DROP;
> > +
> > +	bpf_sk_select_reuseport(reuse_md, &reuseport_map, key, flags);
> > +
> > +	return SK_PASS;
> > +}
> > +
> > +char _license[] SEC("license") = "GPL";
> > -- 
> > 2.30.2
> >