netdev - Re: [RFC bpf-next 0/5] Extend SOCKMAP to store listening sockets

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Message-ID: <20191028204255.jmkraj3xlp346xz4@kafai-mbp.dhcp.thefacebook.com>
Date:   Mon, 28 Oct 2019 20:42:59 +0000
From:   Martin Lau <kafai@...com>
To:     Jakub Sitnicki <jakub@...udflare.com>
CC:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kernel-team@...udflare.com" <kernel-team@...udflare.com>
Subject: Re: [RFC bpf-next 0/5] Extend SOCKMAP to store listening sockets

On Mon, Oct 28, 2019 at 01:35:26PM +0100, Jakub Sitnicki wrote:
> On Mon, Oct 28, 2019 at 06:52 AM CET, Martin Lau wrote:
> > On Tue, Oct 22, 2019 at 01:37:25PM +0200, Jakub Sitnicki wrote:
> >> This patch set is a follow up on a suggestion from LPC '19 discussions to
> >> make SOCKMAP (or a new map type derived from it) a generic type for storing
> >> established as well as listening sockets.
> >>
> >> We found ourselves in need of a map type that keeps references to listening
> >> sockets when working on making the socket lookup programmable, aka BPF
> >> inet_lookup [1].  Initially we repurposed REUSEPORT_SOCKARRAY but found it
> >> problematic to extend due to being tightly coupled with reuseport
> >> logic (see slides [2]).
> >> So we've turned our attention to SOCKMAP instead.
> >>
> >> As it turns out the changes needed to make SOCKMAP suitable for storing
> >> listening sockets are self-contained and have use outside of programming
> >> the socket lookup. Hence this patch set.
> >>
> >> With these patches SOCKMAP can be used in SK_REUSEPORT BPF programs as a
> >> drop-in replacement for REUSEPORT_SOCKARRAY for TCP. This can hopefully
> >> lead to code consolidation between the two map types in the future.
> > What is the plan for UDP support in sockmap?
> 
> It's on our road-map because without SOCKMAP support for UDP we won't be
> able to move away from TPROXY [1] and custom SO_BINDTOPREFIX extension
> [2] for steering new UDP flows to receiving sockets. Also we would like
> to look into using SOCKMAP for connected UDP socket splicing in the
> future [3].
> 
> I was planning to split work as follows:
> 
> 1. SOCKMAP support for listening sockets (this series)
> 2. programmable socket lookup for TCP (cut-down version of [4])
> 3. SOCKMAP support for UDP (work not started)
hmm...It is hard to comment how the full UDP sockmap may
work out without a code attempt because I am not fluent in
sock_map ;)

>From a quick look, it seems there are quite a few things to do.
For example, the TCP_SKB_CB(skb) usage and how that may look
like in UDP.  "struct udp_skb_cb" is 28 bytes while "struct napi_gro_cb"
seems to be 48 bytes already which may need a closer look.

> 4. programmable socket lookup for UDP (rest of [4])
> 
> I'm open to suggestions on how to organize it.
> 
> >> Having said that, the main intention here is to lay groundwork for using
> >> SOCKMAP in the next iteration of programmable socket lookup patches.
> > What may be the minimal to get only lookup work for UDP sockmap?
> > .close() and .unhash()?
> 
> John would know better. I haven't tried doing it yet.
> 
> From just reading the code - override the two proto ops you mentioned,
> close and unhash, and adapt the socket checks in SOCKMAP.
Do your use cases need bpf prog attached to sock_map?

If not, would it be cleaner to delicate another map_type
for lookup-only use case to have both TCP and UDP support.

> 
> -Jakub
> 
> [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__blog.cloudflare.com_how-2Dwe-2Dbuilt-2Dspectrum_&d=DwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=VQnoQ7LvghIj0gVEaiQSUw&m=lSo-FsOeNl_8znZZ07H8I6ZYAinPKTR5C3Cn_Ol3QYQ&s=DZgW8-2Xl1P8NU59ji4ieQLzwWpx4t3gGq_tqB0l3Bo&e= 
> [2] https://lore.kernel.org/netdev/1458699966-3752-1-git-send-email-gilberto.bertin@gmail.com/
> [3] https://lore.kernel.org/bpf/20190828072250.29828-1-jakub@cloudflare.com/
> [4] https://urldefense.proofpoint.com/v2/url?u=https-3A__blog.cloudflare.com_sockmap-2Dtcp-2Dsplicing-2Dof-2Dthe-2Dfuture_&d=DwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=VQnoQ7LvghIj0gVEaiQSUw&m=lSo-FsOeNl_8znZZ07H8I6ZYAinPKTR5C3Cn_Ol3QYQ&s=NerUqb4j7IsGBTcni6Yxk40wf6kTkckHXn3Nx5i4mCU&e=