Re: [PATCH bpf-next v2] bpf, unix: Guard sk_msg-dependent code behind CONFIG_NET_SOCK_MSG

[Jakub Sitnicki <jakub@cloudflare.com>]

On Tue, Jun 23, 2026 at 12:33 PM -07, Alexei Starovoitov wrote:
> On Tue, Jun 23, 2026 at 12:31 PM Kuniyuki Iwashima <kuniyu@google.com> wrote:
>>
>> On Tue, Jun 23, 2026 at 12:21 PM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>> >
>> > On Tue, Jun 23, 2026 at 09:08 AM -07, Kuniyuki Iwashima wrote:
>> > > On Tue, Jun 23, 2026 at 4:20 AM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>> > >>
>> > >> Prepare to decouple BPF_SYSCALL config option from NET_SOCK_MSG. When
>> > >> completed all code paths related to sockmap-based redirects should be
>> > >> guarded by BPF_SYSCALL && NET_SOCK_MSG to allow users to opt out by
>> > >> disabling NET_SOCK_MSG. The implementation of sockmap as a container for
>> > >> socket references would remain under BPF_SYSCALL.
>> > >>
>> > >> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
>> > >> ---
>> > >> Changes in v2:
>> > >> - Handle prot->recvmsg being NULL (Sashiko)
>> > >> - Elaborate on the end goal in description
>> > >> - Link to v1: https://patch.msgid.link/20260622-bpf-sk_msg-split-unix-v1-1-d7e0cb7bb03b@cloudflare.com
>> > >> ---
>> > >>  net/unix/af_unix.c  | 4 ++--
>> > >>  net/unix/unix_bpf.c | 6 ++++++
>> > >>  2 files changed, 8 insertions(+), 2 deletions(-)
>> > >>
>> > >> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
>> > >> index f7a9d55eee8a..84c11c60c75f 100644
>> > >> --- a/net/unix/af_unix.c
>> > >> +++ b/net/unix/af_unix.c
>> > >> @@ -2675,7 +2675,7 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg, size_t si
>> > >>  #ifdef CONFIG_BPF_SYSCALL
>> > >>         const struct proto *prot = READ_ONCE(sk->sk_prot);
>> > >>
>> > >> -       if (prot != &unix_dgram_proto)
>> > >> +       if (prot->recvmsg)
>> > >
>> > > There is no reason to have this dead branch when
>> > > CONFIG_BPF_SYSCALL && !NET_SOCK_MSG.
>> > >
>> > > Let's compile out all sockmap code when both configs
>> > > are not enabled.
>> > >
>> > > Since AF_UNIX differs from TCP/UDP, it can take the
>> > > simpler approach.
>> >
>> > Okay, will put the whole file behind hidden config option like so:
>> >
>> > --- a/net/unix/Kconfig
>> > +++ b/net/unix/Kconfig
>> > @@ -30,3 +30,8 @@ config UNIX_DIAG
>> >         help
>> >           Support for UNIX socket monitoring interface used by the ss tool.
>> >           If unsure, say Y.
>> > +
>> > +config UNIX_BPF
>>
>> Maybe UNIX_BPF_SOCKMAP or something.
>> bpf_iter is supported without this config.
>
> I don't like where it's going.
> I strongly dislike new config knobs.
> I'd rather remove existing knobs.
> What is the motivation?

The goal is to compile out sockmap bits that use sk_msg.
NET_SOCK_MSG is natural, exisiting candidate.
New knob wasn't my idea.

Alternatively, we can do this to avoid the extra knob:

ifdef CONFIG_BPF_SYSCALL
unix-$(CONFIG_NET_SOCK_MSG) += unix_bpf.o
endif