linux-kernel - Re: [PATCH RFC v4 net-next 03/26] bpf: introduce syscall(BPF, ...) and BPF maps

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Message-ID: <CAE40pdcCqu6zBqDgAXBpKHzX=y7hXtz83yEadYTE2yACiqyT3g@mail.gmail.com>
Date:	Thu, 14 Aug 2014 15:28:35 -0700
From:	Brendan Gregg <brendan.d.gregg@...il.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	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>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>, linux-api@...r.kernel.org,
	netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v4 net-next 03/26] bpf: introduce syscall(BPF, ...)
 and BPF maps

On Wed, Aug 13, 2014 at 12:57 AM, Alexei Starovoitov <ast@...mgrid.com> wrote:
[...]
> maps can have different types: hash, bloom filter, radix-tree, etc.
>
> The map is defined by:
>   . type
>   . max number of elements
>   . key size in bytes
>   . value size in bytes

Can values be strings or byte arrays? How would user-level bpf read
them? The two types of uses I'm thinking are:

A. Constructing a custom string in kernel-context, and using that as
the value. Eg, a truncated filename, or a dotted quad IP address, or
the raw contents of a packet.
B. I have a pointer to an existing buffer or string, eg a filename,
that will likely be around for some time (>1s). Instead of the value
storing the string, it could just be a ptr, so long as user-level bpf
has a way to read it.

Also, can keys be strings? I'd ask about multiple keys, but if they
can be a string, I can delimit in the key (eg, "PID:filename").
Thanks,

Brendan

-- 
http://www.brendangregg.com
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