netdev - Re: [net-next v2 2/2] tcp: Add receive timestamp support for receive zerocopy.

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Date:   Mon, 1 Feb 2021 18:20:23 -0800
From:   Arjun Roy <arjunroy@...gle.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Arjun Roy <arjunroy.kdev@...il.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [net-next v2 2/2] tcp: Add receive timestamp support for receive zerocopy.

On Mon, Feb 1, 2021 at 6:06 PM David Ahern <dsahern@...il.com> wrote:
>
> On 1/24/21 11:15 PM, Leon Romanovsky wrote:
> > On Fri, Jan 22, 2021 at 10:55:45PM -0700, David Ahern wrote:
> >> On 1/22/21 9:07 PM, Jakub Kicinski wrote:
> >>> On Wed, 20 Jan 2021 16:41:48 -0800 Arjun Roy wrote:
> >>>> diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
> >>>> index 768e93bd5b51..b216270105af 100644
> >>>> --- a/include/uapi/linux/tcp.h
> >>>> +++ b/include/uapi/linux/tcp.h
> >>>> @@ -353,5 +353,9 @@ struct tcp_zerocopy_receive {
> >>>>    __u64 copybuf_address;  /* in: copybuf address (small reads) */
> >>>>    __s32 copybuf_len; /* in/out: copybuf bytes avail/used or error */
> >>>>    __u32 flags; /* in: flags */
> >>>> +  __u64 msg_control; /* ancillary data */
> >>>> +  __u64 msg_controllen;
> >>>> +  __u32 msg_flags;
> >>>> +  /* __u32 hole;  Next we must add >1 u32 otherwise length checks fail. */
> >>>
> >>> Well, let's hope nobody steps on this landmine.. :)
> >>>
> >>
> >> Past suggestions were made to use anonymous declarations - e.g., __u32
> >> :32; - as a way of reserving the space for future use. That or declare
> >> '__u32 resvd', check that it must be 0 and makes it available for later
> >> (either directly or with a union).
> >
> > This is the schema (reserved field without union) used by the RDMA UAPIs from
> > the beginning (>20 years already) and it works like a charm.
> >
> > Highly recommend :).
> >
>
> agreed.
>
> Arjun: would you mind following up with a patch to make this hole
> explicit and usable for the next extension? Thanks,

Will do.

-Arjun