Re: [PATCH net-next v6 3/3] net/smc: Introduce IPPROTO_SMC

[Mat Martineau <martineau@kernel.org>]

On Wed, 5 Jun 2024, D. Wythe wrote:

> From: "D. Wythe" <alibuda@linux.alibaba.com>
>
> This patch allows to create smc socket via AF_INET,
> similar to the following code,
>
> /* create v4 smc sock */
> v4 = socket(AF_INET, SOCK_STREAM, IPPROTO_SMC);
>
> /* create v6 smc sock */
> v6 = socket(AF_INET6, SOCK_STREAM, IPPROTO_SMC);
>
> There are several reasons why we believe it is appropriate here:
>
> 1. For smc sockets, it actually use IPv4 (AF-INET) or IPv6 (AF-INET6)
> address. There is no AF_SMC address at all.
>
> 2. Create smc socket in the AF_INET(6) path, which allows us to reuse
> the infrastructure of AF_INET(6) path, such as common ebpf hooks.
> Otherwise, smc have to implement it again in AF_SMC path.
>
> Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
> Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
> include/uapi/linux/in.h |   2 +
> net/smc/Makefile        |   2 +-
> net/smc/af_smc.c        |  16 ++++-
> net/smc/smc_inet.c      | 169 ++++++++++++++++++++++++++++++++++++++++++++++++
> net/smc/smc_inet.h      |  22 +++++++
> 5 files changed, 208 insertions(+), 3 deletions(-)
> create mode 100644 net/smc/smc_inet.c
> create mode 100644 net/smc/smc_inet.h
>
> diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
> index e682ab6..0c6322b 100644
> --- a/include/uapi/linux/in.h
> +++ b/include/uapi/linux/in.h
> @@ -83,6 +83,8 @@ enum {
> #define IPPROTO_RAW		IPPROTO_RAW
>   IPPROTO_MPTCP = 262,		/* Multipath TCP connection		*/
> #define IPPROTO_MPTCP		IPPROTO_MPTCP
> +  IPPROTO_SMC = 263,		/* Shared Memory Communications		*/
> +#define IPPROTO_SMC		IPPROTO_SMC

Hello,

It's not required to assign IPPROTO_MPTCP+1 as your new IPPROTO_SMC value. 
Making IPPROTO_MAX larger does increase the size of the inet_diag_table. 
Values from 256 to 261 are usable for IPPROTO_SMC without increasing 
IPPROTO_MAX.

Just for background: When we added IPPROTO_MPTCP, we chose 262 because it 
is IPPROTO_TCP+0x100. The IANA reserved protocol numbers are 8 bits wide 
so we knew we would not conflict with any future additions, and in the 
case of MPTCP is was convenient that truncating the proto value to 8 bits 
would match IPPROTO_TCP.

- Mat

>   IPPROTO_MAX
> };