From: Lorenz Bauer <lmb@cloudflare.com>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
"Daniel Borkmann" <borkmann@iogearbox.net>,
"Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
"Maciej Żenczykowski" <maze@google.com>,
"Shaun Crampton" <shaun@tigera.io>,
"Lorenzo Bianconi" <lorenzo@kernel.org>,
"Marek Majkowski" <marek@cloudflare.com>,
"John Fastabend" <john.fastabend@gmail.com>,
"Jakub Kicinski" <kuba@kernel.org>,
eyal.birger@gmail.com
Subject: Re: [PATCH bpf-next V3 3/6] bpf: add BPF-helper for MTU checking
Date: Mon, 12 Oct 2020 17:54:50 +0200 [thread overview]
Message-ID: <CACAyw9-Ou=T7d6uDC8yKLNUf+QC5sZg_itOEJfhAinKznDdGCA@mail.gmail.com> (raw)
In-Reply-To: <160216615258.882446.12640007391672866038.stgit@firesoul>
On Thu, 8 Oct 2020 at 16:09, Jesper Dangaard Brouer <brouer@redhat.com> wrote:
...
> + * The *flags* argument can be a combination of one or more of the
> + * following values:
> + *
> + * **BPF_MTU_CHK_RELAX**
> + * This flag relax or increase the MTU with room for one
> + * VLAN header (4 bytes) and take into account net device
> + * hard_header_len. This relaxation is also used by the
> + * kernels own forwarding MTU checks.
> + *
> + * **BPF_MTU_CHK_GSO**
> + * This flag will only works for *ctx* **struct sk_buff**.
> + * If packet context contains extra packet segment buffers
> + * (often knows as frags), then those are also checked
> + * against the MTU size.
Maybe this is a documentation issue, but how / when am I expected to
use these flags? I'm really ignorant when it comes to GSO, but could
BPF_MTU_CHK_GSO be implied when the skb is using GSO?
> + *
> + * The *mtu_result* pointer contains the MTU value of the net
> + * device including the L2 header size (usually 14 bytes Ethernet
> + * header). The net device configured MTU is the L3 size, but as
> + * XDP and TX length operate at L2 this helper include L2 header
> + * size in reported MTU.
What does mtu_result represent in the GSO case? I can imagine there
being some funky interactions between skb->len and the return value,
depending on how this is defined.
> + *
> + * Return
> + * * 0 on success, and populate MTU value in *mtu_result* pointer.
> + *
> + * * < 0 if any input argument is invalid (*mtu_result* not updated)
> + *
> + * MTU violations return positive values, but also populate MTU
> + * value in *mtu_result* pointer, as this can be needed for
> + * implemeting PMTU handing:
> + *
> + * * **BPF_MTU_CHK_RET_FRAG_NEEDED**
> + * * **BPF_MTU_CHK_RET_GSO_TOOBIG**
> + *
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
next prev parent reply other threads:[~2020-10-12 15:55 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-08 14:08 [PATCH bpf-next V3 0/6] bpf: New approach for BPF MTU handling Jesper Dangaard Brouer
2020-10-08 14:09 ` [PATCH bpf-next V3 1/6] bpf: Remove MTU check in __bpf_skb_max_len Jesper Dangaard Brouer
2020-10-09 16:12 ` Daniel Borkmann
2020-10-09 18:26 ` Maciej Żenczykowski
2020-10-10 10:25 ` Jesper Dangaard Brouer
2020-10-08 14:09 ` [PATCH bpf-next V3 2/6] bpf: bpf_fib_lookup return MTU value as output when looked up Jesper Dangaard Brouer
2020-10-09 4:05 ` David Ahern
2020-10-08 14:09 ` [PATCH bpf-next V3 3/6] bpf: add BPF-helper for MTU checking Jesper Dangaard Brouer
2020-10-09 23:29 ` Maciej Żenczykowski
2020-10-21 11:32 ` Jesper Dangaard Brouer
2020-10-12 15:54 ` Lorenz Bauer [this message]
2020-10-08 14:09 ` [PATCH bpf-next V3 4/6] bpf: make it possible to identify BPF redirected SKBs Jesper Dangaard Brouer
2020-10-09 16:47 ` Daniel Borkmann
2020-10-09 18:33 ` Maciej Żenczykowski
2020-10-10 11:09 ` Jesper Dangaard Brouer
2020-10-12 21:04 ` Maciej Żenczykowski
2020-10-08 14:09 ` [PATCH bpf-next V3 5/6] bpf: drop MTU check when doing TC-BPF redirect to ingress Jesper Dangaard Brouer
2020-10-09 23:17 ` Maciej Żenczykowski
2020-10-08 14:09 ` [PATCH bpf-next V3 6/6] net: inline and splitup is_skb_forwardable Jesper Dangaard Brouer
2020-10-09 16:33 ` [PATCH bpf-next V3 0/6] bpf: New approach for BPF MTU handling Jakub Kicinski
2020-10-09 20:49 ` John Fastabend
2020-10-09 21:07 ` Alexei Starovoitov
2020-10-09 21:57 ` Maciej Żenczykowski
2020-10-09 23:00 ` Jakub Kicinski
2020-10-10 10:44 ` Jesper Dangaard Brouer
2020-10-10 16:32 ` Jakub Kicinski
2020-10-10 23:52 ` John Fastabend
2020-10-11 23:30 ` Jakub Kicinski
2020-10-13 20:40 ` Jesper Dangaard Brouer
2020-10-13 23:07 ` Jakub Kicinski
2020-10-13 23:37 ` Alexei Starovoitov
2020-10-13 23:54 ` Maciej Żenczykowski
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