netdev - Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN

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Date:	Thu, 24 Mar 2016 23:40:30 +0100
From:	Yann Ylavic <ylavic.dev@...il.com>
To:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Cc:	Tom Herbert <tom@...bertland.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Willy Tarreau <w@....eu>,
	Tolga Ceylan <tolga.ceylan@...il.com>,
	Craig Gallek <cgallek@...gle.com>,
	Josh Snyder <josh@...e406.com>,
	Aaron Conole <aconole@...heb.org>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN_OFF socket option as
 drain mode

On Thu, Mar 24, 2016 at 6:55 PM, Daniel Borkmann wrote:
> On 03/24/2016 06:26 PM, Tom Herbert wrote:
>>
>> On Thu, Mar 24, 2016 at 10:01 AM, Eric Dumazet wrote:
>>>
>>> Really, when BPF can be the solution, we wont allow adding new stuff in
>>> the kernel in the old way.
>>
>> I completely agree with this, but I wonder if we now need a repository
>> of useful BPF modules. So in the case of implementing functionality
>> like in SO_REUSEPORT_LISTEN_OFF that might just become a common BPF
>> program we could direct people to use.
>
> Good point. There's tools/testing/selftests/net/ containing already
> reuseport
> BPF example, maybe it could be extended.

FWIW, I find:

    const struct bpf_insn prog[] = {
        /* BPF_MOV64_REG(BPF_REG_6, BPF_REG_1) */
        { BPF_ALU64 | BPF_MOV | BPF_X, BPF_REG_6, BPF_REG_1, 0, 0 },
        /* BPF_LD_ABS(BPF_W, 0) R0 = (uint32_t)skb[0] */
        { BPF_LD | BPF_ABS | BPF_W, 0, 0, 0, 0 },
        /* BPF_ALU64_IMM(BPF_MOD, BPF_REG_0, mod) */
        { BPF_ALU64 | BPF_MOD | BPF_K, BPF_REG_0, 0, 0, mod },
        /* BPF_EXIT_INSN() */
        { BPF_JMP | BPF_EXIT, 0, 0, 0, 0 }
    };
(and all the way to make it run)

something quite unintuitive from a web server developper perspective,
simply to make SO_REUSEPORT work with forked TCP listeners (probably
as it should out of the box)...

Regards,
Yann.