netdev - Re: [PATCH RFC net-next 03/14] bpf: introduce syscall(BPF, ...) and BPF maps

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Message-ID: <CAMEtUuyKY=haqP11VgXHdfHBkqfB-KxuswygUd7hDPLkOFz9HQ@mail.gmail.com>
Date:	Sat, 28 Jun 2014 23:36:52 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next 03/14] bpf: introduce syscall(BPF, ...) and
 BPF maps

On Sat, Jun 28, 2014 at 6:52 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Sat, Jun 28, 2014 at 1:49 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>>
>> Sorry I don't like 'fd' direction at all.
>> 1. it will make the whole thing very socket specific and 'net' dependent.
>> but the goal here is to be able to use eBPF for tracing in embedded
>> setups. So it's gotta be net independent.
>> 2. sockets are already overloaded with all sorts of stuff. Adding more
>> types of sockets will complicate it a lot.
>> 3. and most important. read/write operations on sockets are not
>> done every nanosecond, whereas lookup operations on bpf maps
>> are done every dozen instructions, so we cannot have any overhead
>> when accessing maps.
>> In other words the verifier is done as static analyzer. I moved all
>> the complexity to verify time, so at run-time the programs are as
>> fast as possible. I'm strongly against run-time checks in critical path,
>> since they kill performance and make the whole approach a lot less usable.
>
> I may have described my suggestion poorly.  I'm suggesting that all of
> these global ids be replaced *for userspace's benefit* with fds.  That
> is, a map would have an associated struct inode, and, when you load an
> eBPF program, you'd pass fds into the kernel instead of global ids.
> The kernel would still compile the eBPF program to use the global ids,
> though.

Hmm. If I understood you correctly, you're suggesting to do it similar
to ipc/mqueue, shmem, sockets do. By registering and mounting
a file system and providing all superblock and inode hooks… and
probably have its own namespace type… hmm… may be. That's
quite a bit of work to put lightly. As I said in the other email the first
step is root only and all these complexity just not worth doing
at this stage.
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