Subject: Re: [PATCH bpf-next v1] bpf, sockmap: Introduce tracing capability for sockmap

From: Jakub Sitnicki <[email-masked]>
Date: Thu, 10 Apr 2025 11:14:50 +0200

On Wed, Apr 09, 2025 at 06:29 PM +08, Jiayuan Chen wrote:
> Sockmap has the same high-performance forwarding capability as XDP, but
> operates at Layer 7.
>
> Introduce tracing capability for sockmap, similar to XDP, to trace the
> execution results of BPF programs without modifying the programs
> themselves, similar to the existing trace_xdp_redirect{_map}.
>
> It is crucial for debugging BPF programs, especially in production
> environments.
>
> Additionally, a header file was added to bpf_trace.h to automatically
> generate tracepoints.
>
> Test results:
> $ echo "1" > /sys/kernel/tracing/events/sockmap/enable
>
> skb:
> sockmap_redirect: sk=00000000d3266a8d, type=skb, family=2, protocol=6, \
> prog_id=73, length=256, action=PASS
>
> msg:
> sockmap_redirect: sk=00000000528c7614, type=msg, family=2, protocol=6, \
> prog_id=185, length=5, action=REDIRECT
>
> tls:
> sockmap_redirect: sk=00000000d04d2224, type=skb, family=2, protocol=6, \
> prog_id=143, length=35, action=PASS
>
> strparser:
> sockmap_skb_strp_parse: sk=00000000ecab0b30, family=2, protocol=6, \
> prog_id=170, size=5
>
> Signed-off-by: Jiayuan Chen <[email-masked]>
> ---
>  MAINTAINERS                    |  1 +
>  include/linux/bpf_trace.h      |  2 +-
>  include/trace/events/sockmap.h | 89 ++++++++++++++++++++++++++++++++++
>  net/core/skmsg.c               |  6 +++
>  4 files changed, 97 insertions(+), 1 deletion(-)
>  create mode 100644 include/trace/events/sockmap.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a7a1d121a83e..578e16d86853 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4420,6 +4420,7 @@ L:	[email-masked]
>  L:	[email-masked]
>  S:	Maintained
>  F:	include/linux/skmsg.h
> +F:	include/trace/events/sockmap.h
>  F:	net/core/skmsg.c
>  F:	net/core/sock_map.c
>  F:	net/ipv4/tcp_bpf.c
> diff --git a/include/linux/bpf_trace.h b/include/linux/bpf_trace.h
> index ddf896abcfb6..896346fb2b46 100644
> --- a/include/linux/bpf_trace.h
> +++ b/include/linux/bpf_trace.h
> @@ -3,5 +3,5 @@
>  #define __LINUX_BPF_TRACE_H__
>  
>  #include <trace/events/xdp.h>
> -
> +#include <trace/events/sockmap.h>
>  #endif /* __LINUX_BPF_TRACE_H__ */
> diff --git a/include/trace/events/sockmap.h b/include/trace/events/sockmap.h
> new file mode 100644
> index 000000000000..2a69b011e88f
> --- /dev/null
> +++ b/include/trace/events/sockmap.h
> @@ -0,0 +1,89 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM sockmap
> +
> +#if !defined(_TRACE_SOCKMAP_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_SOCKMAP_H
> +
> +#include <linux/filter.h>
> +#include <linux/tracepoint.h>
> +#include <linux/bpf.h>
> +#include <linux/skmsg.h>
> +
> +TRACE_DEFINE_ENUM(__SK_DROP);
> +TRACE_DEFINE_ENUM(__SK_PASS);
> +TRACE_DEFINE_ENUM(__SK_REDIRECT);
> +TRACE_DEFINE_ENUM(__SK_NONE);
> +
> +#define show_act(x) \
> +	__print_symbolic(x, \
> +		{ __SK_DROP,		"DROP" }, \
> +		{ __SK_PASS,		"PASS" }, \
> +		{ __SK_REDIRECT,	"REDIRECT" }, \
> +		{ __SK_NONE,		"NONE" })
> +
> +#define trace_sockmap_skmsg_redirect(sk, prog, msg, act)	\
> +	trace_sockmap_redirect((sk), "msg", (prog), (msg)->sg.size, (act))
> +
> +#define trace_sockmap_skb_redirect(sk, prog, skb, act)		\
> +	trace_sockmap_redirect((sk), "skb", (prog), (skb)->len, (act))
> +
> +TRACE_EVENT(sockmap_redirect,
> +	    TP_PROTO(const struct sock *sk, const char *type,
> +		     const struct bpf_prog *prog, int length, int act),
> +	    TP_ARGS(sk, type, prog, length, act),
> +
> +	TP_STRUCT__entry(
> +		__field(const void *, sk)
> +		__field(const char *, type)
> +		__field(__u16, family)
> +		__field(__u16, protocol)
> +		__field(int, prog_id)
> +		__field(int, length)
> +		__field(int, act)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->sk		= sk;
> +		__entry->type		= type;
> +		__entry->family		= sk->sk_family;
> +		__entry->protocol	= sk->sk_protocol;
> +		__entry->prog_id	= prog->aux->id;
> +		__entry->length		= length;
> +		__entry->act		= act;
> +	),
> +
> +	TP_printk("sk=%p, type=%s, family=%d, protocol=%d, prog_id=%d, length=%d, action=%s",
> +		  __entry->sk, __entry->type, __entry->family, __entry->protocol,
> +		  __entry->prog_id, __entry->length,
> +		  show_act(__entry->act))

sk address is useful if you're going to attach a bpf program to the
tracepoint. Not so much if you're printing the recorded trace.

I'd print the netns and the socket inode instead, or in addition to.
These can be cross-referenced against `lsns` and `ss` output.

> +);
> +
> +TRACE_EVENT(sockmap_skb_strp_parse,
> +	    TP_PROTO(const struct sock *sk, const struct bpf_prog *prog,
> +		     int size),
> +	    TP_ARGS(sk, prog, size),
> +
> +	TP_STRUCT__entry(
> +		__field(const void *, sk)
> +		__field(__u16, family)
> +		__field(__u16, protocol)
> +		__field(int, prog_id)
> +		__field(int, size)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->sk		= sk;
> +		__entry->family		= sk->sk_family;
> +		__entry->protocol	= sk->sk_protocol;
> +		__entry->prog_id	= prog->aux->id;
> +		__entry->size		= size;
> +	),
> +
> +	TP_printk("sk=%p, family=%d, protocol=%d, prog_id=%d, size=%d",
> +		  __entry->sk, __entry->family, __entry->protocol,
> +		  __entry->prog_id, __entry->size)
> +);
> +#endif /* _TRACE_SOCKMAP_H */
> +
> +#include <trace/define_trace.h>