From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [RFC PATCH 1/5] bpf: add PHYS_DEV prog type for early driver filter Date: Mon, 04 Apr 2016 15:36:58 +0200 Message-ID: <57026DFA.3090201@iogearbox.net> References: <1459560118-5582-1-git-send-email-bblanco@plumgrid.com> <1459560118-5582-2-git-send-email-bblanco@plumgrid.com> <57022A85.6040002@iogearbox.net> <20160404150700.1456ae80@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: Brenden Blanco , davem@davemloft.net, netdev@vger.kernel.org, tom@herbertland.com, alexei.starovoitov@gmail.com, gerlitz@mellanox.com, john.fastabend@gmail.com To: Jesper Dangaard Brouer Return-path: Received: from www62.your-server.de ([213.133.104.62]:33802 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752017AbcDDNhH (ORCPT ); Mon, 4 Apr 2016 09:37:07 -0400 In-Reply-To: <20160404150700.1456ae80@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 04/04/2016 03:07 PM, Jesper Dangaard Brouer wrote: > On Mon, 04 Apr 2016 10:49:09 +0200 Daniel Borkmann wrote: >> On 04/02/2016 03:21 AM, Brenden Blanco wrote: >>> Add a new bpf prog type that is intended to run in early stages of the >>> packet rx path. Only minimal packet metadata will be available, hence a new >>> context type, struct xdp_metadata, is exposed to userspace. So far only >>> expose the readable packet length, and only in read mode. >>> >>> The PHYS_DEV name is chosen to represent that the program is meant only >>> for physical adapters, rather than all netdevs. >>> >>> While the user visible struct is new, the underlying context must be >>> implemented as a minimal skb in order for the packet load_* instructions >>> to work. The skb filled in by the driver must have skb->len, skb->head, >>> and skb->data set, and skb->data_len == 0. >>> > [...] >> >> Do you plan to support bpf_skb_load_bytes() as well? I like using >> this API especially when dealing with larger chunks (>4 bytes) to >> load into stack memory, plus content is kept in network byte order. >> >> What about other helpers such as bpf_skb_store_bytes() et al that >> work on skbs. Do you intent to reuse them as is and thus populate >> the per cpu skb with needed fields (faking linear data), or do you >> see larger obstacles that prevent for this? > > Argh... maybe the minimal pseudo/fake SKB is the wrong "signal" to send > to users of this API. > > The hole idea is that an SKB is NOT allocated yet, and not needed at > this level. If we start supporting calling underlying SKB functions, > then we will end-up in the same place (performance wise). I'm talking about the current skb-related BPF helper functions we have, so the question is how much from that code we have we can reuse under these constraints (obviously things like the tunnel helpers are a different story) and if that trade-off is acceptable for us. I'm also thinking that, for example, if you need to parse the packet data anyway for a drop verdict, you might as well pass some meta data (that is set in the real skb later on) for those packets that go up the stack.