diff mbox series

[bpf-next,v4,1/7] bpf: add bpf_skc_to_mptcp_sock_proto

Message ID 20220513224827.662254-2-mathew.j.martineau@linux.intel.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series bpf: mptcp: Support for mptcp_sock | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1820 this patch: 1820
netdev/cc_maintainers warning 10 maintainers not CCed: kafai@fb.com john.fastabend@gmail.com pabeni@redhat.com kuba@kernel.org yhs@fb.com kpsingh@kernel.org davem@davemloft.net songliubraving@fb.com rostedt@goodmis.org mingo@redhat.com
netdev/build_clang success Errors and warnings before: 196 this patch: 196
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1830 this patch: 1830
netdev/checkpatch warning WARNING: added, moved or deleted file(s), does MAINTAINERS need updating? WARNING: line length of 87 exceeds 80 columns WARNING: line length of 94 exceeds 80 columns
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
bpf/vmtest-bpf-next-PR success PR summary
bpf/vmtest-bpf-next-VM_Test-1 success Logs for Kernel LATEST on ubuntu-latest with gcc
bpf/vmtest-bpf-next-VM_Test-2 success Logs for Kernel LATEST on ubuntu-latest with llvm-15
bpf/vmtest-bpf-next-VM_Test-3 success Logs for Kernel LATEST on z15 with gcc

Commit Message

Mat Martineau May 13, 2022, 10:48 p.m. UTC 
From: Geliang Tang <geliang.tang@suse.com>

This patch implements a new struct bpf_func_proto, named
bpf_skc_to_mptcp_sock_proto. Define a new bpf_id BTF_SOCK_TYPE_MPTCP,
and a new helper bpf_skc_to_mptcp_sock(), which invokes another new
helper bpf_mptcp_sock_from_subflow() in net/mptcp/bpf.c to get struct
mptcp_sock from a given subflow socket.

v2: Emit BTF type, add func_id checks in verifier.c and bpf_trace.c,
remove build check for CONFIG_BPF_JIT

Co-developed-by: Nicolas Rybowski <nicolas.rybowski@tessares.net>
Signed-off-by: Nicolas Rybowski <nicolas.rybowski@tessares.net>
Co-developed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
---
 include/linux/bpf.h            |  1 +
 include/linux/btf_ids.h        |  3 ++-
 include/net/mptcp.h            |  6 ++++++
 include/uapi/linux/bpf.h       |  7 +++++++
 kernel/bpf/verifier.c          |  1 +
 kernel/trace/bpf_trace.c       |  2 ++
 net/core/filter.c              | 18 ++++++++++++++++++
 net/mptcp/Makefile             |  2 ++
 net/mptcp/bpf.c                | 22 ++++++++++++++++++++++
 scripts/bpf_doc.py             |  2 ++
 tools/include/uapi/linux/bpf.h |  7 +++++++
 11 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 net/mptcp/bpf.c

Comments

Martin KaFai Lau May 17, 2022, 1:07 a.m. UTC | #1 
On Fri, May 13, 2022 at 03:48:21PM -0700, Mat Martineau wrote:
[ ... ]

> diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> index 8b1afd6f5cc4..2ba09de955c7 100644
> --- a/include/net/mptcp.h
> +++ b/include/net/mptcp.h
> @@ -284,4 +284,10 @@ static inline int mptcpv6_init(void) { return 0; }
>  static inline void mptcpv6_handle_mapped(struct sock *sk, bool mapped) { }
>  #endif
>  
> +#if defined(CONFIG_MPTCP) && defined(CONFIG_BPF_SYSCALL)
> +struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk);
Can this be inline ?

> +#else
> +static inline struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk) { return NULL; }
> +#endif
> +
>  #endif /* __NET_MPTCP_H */

[ ... ]

> diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
> new file mode 100644
> index 000000000000..535602ba2582
> --- /dev/null
> +++ b/net/mptcp/bpf.c
> @@ -0,0 +1,22 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Multipath TCP
> + *
> + * Copyright (c) 2020, Tessares SA.
> + * Copyright (c) 2022, SUSE.
> + *
> + * Author: Nicolas Rybowski <nicolas.rybowski@tessares.net>
> + */
> +
> +#define pr_fmt(fmt) "MPTCP: " fmt
> +
> +#include <linux/bpf.h>
> +#include "protocol.h"
> +
> +struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
> +{
> +	if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
> +		return mptcp_sk(mptcp_subflow_ctx(sk)->conn);
> +
> +	return NULL;
> +}
> +EXPORT_SYMBOL(bpf_mptcp_sock_from_subflow);
Is EXPORT_SYMBOL needed ?
Geliang Tang May 17, 2022, 5:26 a.m. UTC | #2 
Martin KaFai Lau <kafai@fb.com> 于2022年5月17日周二 09:07写道：
>
> On Fri, May 13, 2022 at 03:48:21PM -0700, Mat Martineau wrote:
> [ ... ]
>
> > diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> > index 8b1afd6f5cc4..2ba09de955c7 100644
> > --- a/include/net/mptcp.h
> > +++ b/include/net/mptcp.h
> > @@ -284,4 +284,10 @@ static inline int mptcpv6_init(void) { return 0; }
> >  static inline void mptcpv6_handle_mapped(struct sock *sk, bool mapped) { }
> >  #endif
> >
> > +#if defined(CONFIG_MPTCP) && defined(CONFIG_BPF_SYSCALL)
> > +struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk);
> Can this be inline ?

This function can't be inline since it uses struct mptcp_subflow_context.

mptcp_subflow_context is defined in net/mptcp/protocol.h, and we don't
want to export it to user space in net/mptcp/protocol.h.

>
> > +#else
> > +static inline struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk) { return NULL; }
> > +#endif
> > +
> >  #endif /* __NET_MPTCP_H */
>
> [ ... ]
>
> > diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
> > new file mode 100644
> > index 000000000000..535602ba2582
> > --- /dev/null
> > +++ b/net/mptcp/bpf.c
> > @@ -0,0 +1,22 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Multipath TCP
> > + *
> > + * Copyright (c) 2020, Tessares SA.
> > + * Copyright (c) 2022, SUSE.
> > + *
> > + * Author: Nicolas Rybowski <nicolas.rybowski@tessares.net>
> > + */
> > +
> > +#define pr_fmt(fmt) "MPTCP: " fmt
> > +
> > +#include <linux/bpf.h>
> > +#include "protocol.h"
> > +
> > +struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
> > +{
> > +     if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
> > +             return mptcp_sk(mptcp_subflow_ctx(sk)->conn);
> > +
> > +     return NULL;
> > +}
> > +EXPORT_SYMBOL(bpf_mptcp_sock_from_subflow);
> Is EXPORT_SYMBOL needed ?

Will drop in v5.

Thanks,
-Geliang

>
Alexei Starovoitov May 17, 2022, 5 p.m. UTC | #3 
On Mon, May 16, 2022 at 10:26 PM Geliang Tang <geliangtang@gmail.com> wrote:
>
> Martin KaFai Lau <kafai@fb.com> 于2022年5月17日周二 09:07写道：
> >
> > On Fri, May 13, 2022 at 03:48:21PM -0700, Mat Martineau wrote:
> > [ ... ]
> >
> > > diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> > > index 8b1afd6f5cc4..2ba09de955c7 100644
> > > --- a/include/net/mptcp.h
> > > +++ b/include/net/mptcp.h
> > > @@ -284,4 +284,10 @@ static inline int mptcpv6_init(void) { return 0; }
> > >  static inline void mptcpv6_handle_mapped(struct sock *sk, bool mapped) { }
> > >  #endif
> > >
> > > +#if defined(CONFIG_MPTCP) && defined(CONFIG_BPF_SYSCALL)
> > > +struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk);
> > Can this be inline ?
>
> This function can't be inline since it uses struct mptcp_subflow_context.
>
> mptcp_subflow_context is defined in net/mptcp/protocol.h, and we don't
> want to export it to user space in net/mptcp/protocol.h.

The above function can be made static inline in a header file.
That doesn't automatically expose it to user space.
Mat Martineau May 19, 2022, 12:38 a.m. UTC | #4 
On Tue, 17 May 2022, Alexei Starovoitov wrote:

> On Mon, May 16, 2022 at 10:26 PM Geliang Tang <geliangtang@gmail.com> wrote:
>>
>> Martin KaFai Lau <kafai@fb.com> 于2022年5月17日周二 09:07写道：
>>>
>>> On Fri, May 13, 2022 at 03:48:21PM -0700, Mat Martineau wrote:
>>> [ ... ]
>>>
>>>> diff --git a/include/net/mptcp.h b/include/net/mptcp.h
>>>> index 8b1afd6f5cc4..2ba09de955c7 100644
>>>> --- a/include/net/mptcp.h
>>>> +++ b/include/net/mptcp.h
>>>> @@ -284,4 +284,10 @@ static inline int mptcpv6_init(void) { return 0; }
>>>>  static inline void mptcpv6_handle_mapped(struct sock *sk, bool mapped) { }
>>>>  #endif
>>>>
>>>> +#if defined(CONFIG_MPTCP) && defined(CONFIG_BPF_SYSCALL)
>>>> +struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk);
>>> Can this be inline ?
>>
>> This function can't be inline since it uses struct mptcp_subflow_context.
>>
>> mptcp_subflow_context is defined in net/mptcp/protocol.h, and we don't
>> want to export it to user space in net/mptcp/protocol.h.
>
> The above function can be made static inline in a header file.
> That doesn't automatically expose it to user space.
>

True, it's not a question of userspace exposure. But making this one 
function inline involves a bunch of churn in the (non-BPF) mptcp headers 
that I'd rather avoid. The definitions in protocol.h are there because 
they aren't relevant outside of the mptcp subsystem code.

Does making this one function inline benefit BPF, specifically, in a 
meaningful way? If not, I'd like to leave it as-is.

--
Mat Martineau
Intel
Martin KaFai Lau May 19, 2022, 5:58 p.m. UTC | #5 
On Wed, May 18, 2022 at 05:38:43PM -0700, Mat Martineau wrote:
> On Tue, 17 May 2022, Alexei Starovoitov wrote:
> 
> > On Mon, May 16, 2022 at 10:26 PM Geliang Tang <geliangtang@gmail.com> wrote:
> > > 
> > > Martin KaFai Lau <kafai@fb.com> 于2022年5月17日周二 09:07写道：
> > > > 
> > > > On Fri, May 13, 2022 at 03:48:21PM -0700, Mat Martineau wrote:
> > > > [ ... ]
> > > > 
> > > > > diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> > > > > index 8b1afd6f5cc4..2ba09de955c7 100644
> > > > > --- a/include/net/mptcp.h
> > > > > +++ b/include/net/mptcp.h
> > > > > @@ -284,4 +284,10 @@ static inline int mptcpv6_init(void) { return 0; }
> > > > >  static inline void mptcpv6_handle_mapped(struct sock *sk, bool mapped) { }
> > > > >  #endif
> > > > > 
> > > > > +#if defined(CONFIG_MPTCP) && defined(CONFIG_BPF_SYSCALL)
> > > > > +struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk);
> > > > Can this be inline ?
> > > 
> > > This function can't be inline since it uses struct mptcp_subflow_context.
> > > 
> > > mptcp_subflow_context is defined in net/mptcp/protocol.h, and we don't
> > > want to export it to user space in net/mptcp/protocol.h.
> > 
> > The above function can be made static inline in a header file.
> > That doesn't automatically expose it to user space.
> > 
> 
> True, it's not a question of userspace exposure. But making this one
> function inline involves a bunch of churn in the (non-BPF) mptcp headers
> that I'd rather avoid. The definitions in protocol.h are there because they
> aren't relevant outside of the mptcp subsystem code.
> 
> Does making this one function inline benefit BPF, specifically, in a
> meaningful way?
I believe this is similar to the already inlined mptcp_subflow_ctx().

> If not, I'd like to leave it as-is.
Sure, it is fine to leave it if the churn is too much.

Was suggesting because all other bpf_skc_to_* cast helpers
don't have this call-out.  Just in case if those cast helpers will be
inlined by verifier in the future, this won't be the only one that
got left behind.
diff mbox series

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5061ccd8b2dc..c129c2e2dd95 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2229,6 +2229,7 @@  extern const struct bpf_func_proto bpf_skc_to_tcp_timewait_sock_proto;
 extern const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto;
 extern const struct bpf_func_proto bpf_skc_to_udp6_sock_proto;
 extern const struct bpf_func_proto bpf_skc_to_unix_sock_proto;
+extern const struct bpf_func_proto bpf_skc_to_mptcp_sock_proto;
 extern const struct bpf_func_proto bpf_copy_from_user_proto;
 extern const struct bpf_func_proto bpf_snprintf_btf_proto;
 extern const struct bpf_func_proto bpf_snprintf_proto;
diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
index bc5d9cc34e4c..335a19092368 100644
--- a/include/linux/btf_ids.h
+++ b/include/linux/btf_ids.h
@@ -178,7 +178,8 @@  extern struct btf_id_set name;
 	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_UNIX, unix_sock)
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UNIX, unix_sock)			\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_MPTCP, mptcp_sock)
 
 enum {
 #define BTF_SOCK_TYPE(name, str) name,
diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 8b1afd6f5cc4..2ba09de955c7 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -284,4 +284,10 @@  static inline int mptcpv6_init(void) { return 0; }
 static inline void mptcpv6_handle_mapped(struct sock *sk, bool mapped) { }
 #endif
 
+#if defined(CONFIG_MPTCP) && defined(CONFIG_BPF_SYSCALL)
+struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk);
+#else
+static inline struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk) { return NULL; }
+#endif
+
 #endif /* __NET_MPTCP_H */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 0210f85131b3..56688bee20d9 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5172,6 +5172,12 @@  union bpf_attr {
  * 	Return
  * 		Map value associated to *key* on *cpu*, or **NULL** if no entry
  * 		was found or *cpu* is invalid.
+ *
+ * struct mptcp_sock *bpf_skc_to_mptcp_sock(void *sk)
+ *	Description
+ *		Dynamically cast a *sk* pointer to a *mptcp_sock* pointer.
+ *	Return
+ *		*sk* if casting is valid, or **NULL** otherwise.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5370,6 +5376,7 @@  union bpf_attr {
 	FN(ima_file_hash),		\
 	FN(kptr_xchg),			\
 	FN(map_lookup_percpu_elem),     \
+	FN(skc_to_mptcp_sock),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 05c1b6656824..10ed10b24860 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -509,6 +509,7 @@  static bool is_ptr_cast_function(enum bpf_func_id func_id)
 		func_id == BPF_FUNC_skc_to_tcp_sock ||
 		func_id == BPF_FUNC_skc_to_tcp6_sock ||
 		func_id == BPF_FUNC_skc_to_udp6_sock ||
+		func_id == BPF_FUNC_skc_to_mptcp_sock ||
 		func_id == BPF_FUNC_skc_to_tcp_timewait_sock ||
 		func_id == BPF_FUNC_skc_to_tcp_request_sock;
 }
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 7141ca8a1c2d..10b157a6d73e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1705,6 +1705,8 @@  tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_skc_to_udp6_sock_proto;
 	case BPF_FUNC_skc_to_unix_sock:
 		return &bpf_skc_to_unix_sock_proto;
+	case BPF_FUNC_skc_to_mptcp_sock:
+		return &bpf_skc_to_mptcp_sock_proto;
 	case BPF_FUNC_sk_storage_get:
 		return &bpf_sk_storage_get_tracing_proto;
 	case BPF_FUNC_sk_storage_delete:
diff --git a/net/core/filter.c b/net/core/filter.c
index fe0da529d00f..5af58eb48587 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -78,6 +78,7 @@ 
 #include <linux/btf_ids.h>
 #include <net/tls.h>
 #include <net/xdp.h>
+#include <net/mptcp.h>
 
 static const struct bpf_func_proto *
 bpf_sk_base_func_proto(enum bpf_func_id func_id);
@@ -11281,6 +11282,20 @@  const struct bpf_func_proto bpf_skc_to_unix_sock_proto = {
 	.ret_btf_id		= &btf_sock_ids[BTF_SOCK_TYPE_UNIX],
 };
 
+BPF_CALL_1(bpf_skc_to_mptcp_sock, struct sock *, sk)
+{
+	BTF_TYPE_EMIT(struct mptcp_sock);
+	return (unsigned long)bpf_mptcp_sock_from_subflow(sk);
+}
+
+const struct bpf_func_proto bpf_skc_to_mptcp_sock_proto = {
+	.func		= bpf_skc_to_mptcp_sock,
+	.gpl_only	= false,
+	.ret_type	= RET_PTR_TO_BTF_ID_OR_NULL,
+	.arg1_type	= ARG_PTR_TO_SOCK_COMMON,
+	.ret_btf_id	= &btf_sock_ids[BTF_SOCK_TYPE_MPTCP],
+};
+
 BPF_CALL_1(bpf_sock_from_file, struct file *, file)
 {
 	return (unsigned long)sock_from_file(file);
@@ -11323,6 +11338,9 @@  bpf_sk_base_func_proto(enum bpf_func_id func_id)
 	case BPF_FUNC_skc_to_unix_sock:
 		func = &bpf_skc_to_unix_sock_proto;
 		break;
+	case BPF_FUNC_skc_to_mptcp_sock:
+		func = &bpf_skc_to_mptcp_sock_proto;
+		break;
 	case BPF_FUNC_ktime_get_coarse_ns:
 		return &bpf_ktime_get_coarse_ns_proto;
 	default:
diff --git a/net/mptcp/Makefile b/net/mptcp/Makefile
index e54daceac58b..99dddf08ca73 100644
--- a/net/mptcp/Makefile
+++ b/net/mptcp/Makefile
@@ -10,3 +10,5 @@  obj-$(CONFIG_INET_MPTCP_DIAG) += mptcp_diag.o
 mptcp_crypto_test-objs := crypto_test.o
 mptcp_token_test-objs := token_test.o
 obj-$(CONFIG_MPTCP_KUNIT_TEST) += mptcp_crypto_test.o mptcp_token_test.o
+
+obj-$(CONFIG_BPF_SYSCALL) += bpf.o
diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
new file mode 100644
index 000000000000..535602ba2582
--- /dev/null
+++ b/net/mptcp/bpf.c
@@ -0,0 +1,22 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Multipath TCP
+ *
+ * Copyright (c) 2020, Tessares SA.
+ * Copyright (c) 2022, SUSE.
+ *
+ * Author: Nicolas Rybowski <nicolas.rybowski@tessares.net>
+ */
+
+#define pr_fmt(fmt) "MPTCP: " fmt
+
+#include <linux/bpf.h>
+#include "protocol.h"
+
+struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
+{
+	if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
+		return mptcp_sk(mptcp_subflow_ctx(sk)->conn);
+
+	return NULL;
+}
+EXPORT_SYMBOL(bpf_mptcp_sock_from_subflow);
diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
index 096625242475..d5452f7eb996 100755
--- a/scripts/bpf_doc.py
+++ b/scripts/bpf_doc.py
@@ -633,6 +633,7 @@  class PrinterHelpers(Printer):
             'struct socket',
             'struct file',
             'struct bpf_timer',
+            'struct mptcp_sock',
     ]
     known_types = {
             '...',
@@ -682,6 +683,7 @@  class PrinterHelpers(Printer):
             'struct socket',
             'struct file',
             'struct bpf_timer',
+            'struct mptcp_sock',
     }
     mapped_types = {
             'u8': '__u8',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 0210f85131b3..56688bee20d9 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5172,6 +5172,12 @@  union bpf_attr {
  * 	Return
  * 		Map value associated to *key* on *cpu*, or **NULL** if no entry
  * 		was found or *cpu* is invalid.
+ *
+ * struct mptcp_sock *bpf_skc_to_mptcp_sock(void *sk)
+ *	Description
+ *		Dynamically cast a *sk* pointer to a *mptcp_sock* pointer.
+ *	Return
+ *		*sk* if casting is valid, or **NULL** otherwise.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5370,6 +5376,7 @@  union bpf_attr {
 	FN(ima_file_hash),		\
 	FN(kptr_xchg),			\
 	FN(map_lookup_percpu_elem),     \
+	FN(skc_to_mptcp_sock),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper