Re: [PATCH bpf-next 1/2] bpf: af_unix: Implement BPF iterator for UNIX domain socket.

[Kuniyuki Iwashima <kuniyu@amazon.co.jp>]

From:   Yonghong Song <yhs@fb.com>
Date:   Thu, 29 Jul 2021 23:24:41 -0700
> On 7/29/21 4:36 PM, Kuniyuki Iwashima wrote:
> > This patch implements the BPF iterator for the UNIX domain socket.
> > 
> > Currently, the batch optimization introduced for the TCP iterator in the
> > commit 04c7820b776f ("bpf: tcp: Bpf iter batching and lock_sock") is not
> > applied.  It will require replacing the big lock for the hash table with
> > small locks for each hash list not to block other processes.
> 
> Thanks for the contribution. The patch looks okay except
> missing seq_ops->stop implementation, see below for more explanation.
> 
> > 
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
> > ---
> >   include/linux/btf_ids.h |  3 +-
> >   net/unix/af_unix.c      | 78 +++++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 80 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
> > index 57890b357f85..bed4b9964581 100644
> > --- a/include/linux/btf_ids.h
> > +++ b/include/linux/btf_ids.h
> > @@ -172,7 +172,8 @@ extern struct btf_id_set name;
> >   	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_TW, tcp_timewait_sock)		\
> >   	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP6, tcp6_sock)			\
> >   	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP, udp_sock)			\
> > -	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP6, udp6_sock)
> > +	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP6, udp6_sock)			\
> > +	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UNIX, unix_sock)
> >   
> >   enum {
> >   #define BTF_SOCK_TYPE(name, str) name,
> > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> > index 89927678c0dc..d45ad87e3a49 100644
> > --- a/net/unix/af_unix.c
> > +++ b/net/unix/af_unix.c
> > @@ -113,6 +113,7 @@
> >   #include <linux/security.h>
> >   #include <linux/freezer.h>
> >   #include <linux/file.h>
> > +#include <linux/btf_ids.h>
> >   
> >   #include "scm.h"
> >   
> > @@ -2935,6 +2936,49 @@ static const struct seq_operations unix_seq_ops = {
> >   	.stop   = unix_seq_stop,
> >   	.show   = unix_seq_show,
> >   };
> > +
> > +#ifdef CONFIG_BPF_SYSCALL
> > +struct bpf_iter__unix {
> > +	__bpf_md_ptr(struct bpf_iter_meta *, meta);
> > +	__bpf_md_ptr(struct unix_sock *, unix_sk);
> > +	uid_t uid __aligned(8);
> > +};
> > +
> > +static int unix_prog_seq_show(struct bpf_prog *prog, struct bpf_iter_meta *meta,
> > +			      struct unix_sock *unix_sk, uid_t uid)
> > +{
> > +	struct bpf_iter__unix ctx;
> > +
> > +	meta->seq_num--;  /* skip SEQ_START_TOKEN */
> > +	ctx.meta = meta;
> > +	ctx.unix_sk = unix_sk;
> > +	ctx.uid = uid;
> > +	return bpf_iter_run_prog(prog, &ctx);
> > +}
> > +
> > +static int bpf_iter_unix_seq_show(struct seq_file *seq, void *v)
> > +{
> > +	struct bpf_iter_meta meta;
> > +	struct bpf_prog *prog;
> > +	struct sock *sk = v;
> > +	uid_t uid;
> > +
> > +	if (v == SEQ_START_TOKEN)
> > +		return 0;
> > +
> > +	uid = from_kuid_munged(seq_user_ns(seq), sock_i_uid(sk));
> > +	meta.seq = seq;
> > +	prog = bpf_iter_get_info(&meta, false);
> > +	return unix_prog_seq_show(prog, &meta, v, uid);
> > +}
> > +
> > +static const struct seq_operations bpf_iter_unix_seq_ops = {
> > +	.start	= unix_seq_start,
> > +	.next	= unix_seq_next,
> > +	.stop	= unix_seq_stop,
> 
> Although it is not required for /proc/net/unix, we should still
> implement bpf_iter version of seq_ops->stop here. The main purpose
> of bpf_iter specific seq_ops->stop is to call bpf program one
> more time after ALL elements have been traversed. Such
> functionality is implemented in all other bpf_iter variants.

Thanks for your review!
I will implement the extra call in the next spin.

Just out of curiosity, is there a specific use case for the last call?