[PATCH 5/8] net: define IPPROTO_SMBDIRECT and SOL_SMBDIRECT constants

This patch adds IPPROTO_SMBDIRECT and SOL_SMBDIRECT constants to the
networking subsystem. These definitions are essential for applications
to set socket options and protocol identifiers related to the SMBDIRECT
protocol, defined in [MS-SMBD] by Microsoft. It is used as wrapper
around RDMA in order to provide a transport for SMB3, but Microsoft also
uses it as transport for other protocols.

SMBDIRECT works over Infiniband, RoCE and iWarp.
RoCEv2 is based on IP/UDP and iWarp is based on IP/TCP,
so these use IP addresses natively.
Infiniband and RoCEv1 require IPOIB in order to be used for
SMBDIRECT.

So instead of adding a PF_SMBDIRECT, which would only use AF_INET[6],
we use IPPROTO_SMBDIRECT instead, this uses a number not
allocated from IANA, as it would not appear in an IP header.

This is similar to IPPROTO_SMC, IPPROTO_MPTCP and IPPROTO_QUIC,
which are linux specific values for the socket() syscall.

  socket(AF_INET, SOCK_STREAM, IPPROTO_SMBDIRECT);
  socket(AF_INET6, SOCK_STREAM, IPPROTO_SMBDIRECT);

This will allow the existing smbdirect code used by
cifs.ko and ksmbd.ko to be moved behind the socket layer,
so that there's less special handling. Only sock_sendmsg()
sock_recvmsg() are used, so that the main stream handling
is done all the same for tcp, smbdirect and later also quic.

The special RDMA read/write handling will be via direct
function calls as they are currently done for the in kernel
consumers.

As a start __sock_create(kern=0)/sk->sk_kern_sock == 0 will
still cause a -EPROTONOSUPPORT. So only in kernel consumers
will be supported for now.

Once I have developed a stable interface for the RDMA read/write
handling using sendmsg/recvmsg with MSG_OOB and msg_control,
it will also exposed to userspace in order to allow Samba to
use it.

As the numbers of IPPROTO_QUIC (261) and SOL_QUIC (288) [1]
are already used in various (released) userspace applications,
I used 289 for SOL_SMBDIRECT instead of 288.

[1]
https://lore.kernel.org/quic/0cb58f6fcf35ac988660e42704dae9960744a0a7.1763994509.git.lucien.xin@gmail.com/T/#u

Cc: Steve French <[email protected]>
Cc: Tom Talpey <[email protected]>
Cc: Long Li <[email protected]>
Cc: Namjae Jeon <[email protected]>
Cc: David Howells <[email protected]>
Cc: Henrique Carvalho <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: David S. Miller <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: Simon Horman <[email protected]>
Cc: Kuniyuki Iwashima <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Cc: [email protected]
Cc: Xin Long <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Stefan Metzmacher <[email protected]>
---
 include/linux/socket.h  | 2 ++
 include/uapi/linux/in.h | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index ec715ad4bf25..e00cbfdaa8d6 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -401,6 +401,8 @@ struct ucred {
 #define SOL_MCTP	285
 #define SOL_SMC		286
 #define SOL_VSOCK	287
+/* 288 reserved for SOL_QUIC */
+#define SOL_SMBDIRECT	289
 
 /* IPX options */
 #define IPX_TYPE	1
diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
index ced0fc3c3aa5..933d243b1780 100644
--- a/include/uapi/linux/in.h
+++ b/include/uapi/linux/in.h
@@ -85,6 +85,8 @@ enum {
 #define IPPROTO_RAW		IPPROTO_RAW
   IPPROTO_SMC = 256,		/* Shared Memory Communications		*/
 #define IPPROTO_SMC		IPPROTO_SMC
+  IPPROTO_SMBDIRECT = 257,	/* RDMA based transport (mostly used by SMB3) */
+#define IPPROTO_SMBDIRECT	IPPROTO_SMBDIRECT
   IPPROTO_MPTCP = 262,		/* Multipath TCP connection		*/
 #define IPPROTO_MPTCP		IPPROTO_MPTCP
   IPPROTO_MAX
-- 
2.43.0