netdev - Re: [PATCH v2 bpf-next 15/15] selftests/bpf: bpf

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Message-ID: <20220804000417.gmaqry4ecgjlpcvf@kafai-mbp.dhcp.thefacebook.com>
Date:   Wed, 3 Aug 2022 17:04:17 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     sdf@...gle.com
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, kernel-team@...com,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH v2 bpf-next 15/15] selftests/bpf: bpf_setsockopt tests

On Wed, Aug 03, 2022 at 04:30:54PM -0700, sdf@...gle.com wrote:
> > +struct sock_common {
> > +	unsigned short	skc_family;
> > +	unsigned long	skc_flags;
> > +	unsigned char	skc_reuse:4;
> > +	unsigned char	skc_reuseport:1;
> > +	unsigned char	skc_ipv6only:1;
> > +	unsigned char	skc_net_refcnt:1;
> > +} __attribute__((preserve_access_index));
> > +
> > +struct sock {
> > +	struct sock_common	__sk_common;
> > +	__u16			sk_type;
> > +	__u16			sk_protocol;
> > +	int			sk_rcvlowat;
> > +	__u32			sk_mark;
> > +	unsigned long		sk_max_pacing_rate;
> > +	unsigned int		keepalive_time;
> > +	unsigned int		keepalive_intvl;
> > +} __attribute__((preserve_access_index));
> > +
> > +struct tcp_options_received {
> > +	__u16 user_mss;
> > +} __attribute__((preserve_access_index));
> 
> I'm assuming you're not using vmlinux here because it doesn't bring
> it most of the defines? Should we add missing stuff to bpf_tracing_net.h
> instead?
Ah, actually my first attempt was to use vmlinux.h and had
all defines ready for addition to bpf_tracing_net.h. 

However, I hit an issue in reading bitfield.  It is why the
bitfield in the tcp_sock below is sandwiched between __u32.
I think it is likely LLVM and/or CO-RE related. Yonghong is
helping to investigate it.

In the mean time, I define those mini struct here.
Once the bitfield issue is resolved, we can go back to
use vmlinux.h.

> 
> > +struct ipv6_pinfo {
> > +	__u16			recverr:1,
> > +				sndflow:1,
> > +				repflow:1,
> > +				pmtudisc:3,
> > +				padding:1,
> > +				srcprefs:3,
> > +				dontfrag:1,
> > +				autoflowlabel:1,
> > +				autoflowlabel_set:1,
> > +				mc_all:1,
> > +				recverr_rfc4884:1,
> > +				rtalert_isolate:1;
> > +}  __attribute__((preserve_access_index));
> > +
> > +struct inet_sock {
> > +	/* sk and pinet6 has to be the first two members of inet_sock */
> > +	struct sock		sk;
> > +	struct ipv6_pinfo	*pinet6;
> > +} __attribute__((preserve_access_index));
> > +
> > +struct inet_connection_sock {
> > +	__u32			  icsk_user_timeout;
> > +	__u8			  icsk_syn_retries;
> > +} __attribute__((preserve_access_index));
> > +
> > +struct tcp_sock {
> > +	struct inet_connection_sock	inet_conn;
> > +	struct tcp_options_received rx_opt;
> > +	__u8	save_syn:2,
> > +		syn_data:1,
> > +		syn_fastopen:1,
> > +		syn_fastopen_exp:1,
> > +		syn_fastopen_ch:1,
> > +		syn_data_acked:1,
> > +		is_cwnd_limited:1;
> > +	__u32	window_clamp;
> > +	__u8	nonagle     : 4,
> > +		thin_lto    : 1,
> > +		recvmsg_inq : 1,
> > +		repair      : 1,
> > +		frto        : 1;
> > +	__u32	notsent_lowat;
> > +	__u8	keepalive_probes;
> > +	unsigned int		keepalive_time;
> > +	unsigned int		keepalive_intvl;
> > +} __attribute__((preserve_access_index));
> > +
> > +struct socket {
> > +	struct sock *sk;
> > +} __attribute__((preserve_access_index));
> > +
> > +struct loop_ctx {
> > +	void *ctx;
> > +	struct sock *sk;
> > +};
> > +
> > +static int __bpf_getsockopt(void *ctx, struct sock *sk,
> > +			    int level, int opt, int *optval,
> > +			    int optlen)
> > +{
> > +	if (level == SOL_SOCKET) {
> > +		switch (opt) {
> > +		case SO_REUSEADDR:
> > +			*optval = !!(sk->__sk_common.skc_reuse);
> > +			break;
> > +		case SO_KEEPALIVE:
> > +			*optval = !!(sk->__sk_common.skc_flags & (1UL << 3));
> > +			break;
> > +		case SO_RCVLOWAT:
> > +			*optval = sk->sk_rcvlowat;
> > +			break;
> 
> What's the idea with the options above? Why not allow them in
> bpf_getsockopt instead?
I am planning to refactor the bpf_getsockopt also,
so trying to avoid adding more dup code at this point
while they can directly be read from sk through PTR_TO_BTF_ID.

btw, since we are on bpf_getsockopt(), do you still see a usage on
bpf_getsockopt() for those 'integer-value' optnames that can be
easily read from the sk pointer ?

> 
> > +		case SO_MARK:
> > +			*optval = sk->sk_mark;
> > +			break;
> 
> SO_MARK should be handled by bpf_getsockopt ?
Good point, will remove SO_MARK case.

Thanks for the review!