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

From: Brendan Gregg
Date: Thu Aug 14 2014 - 18:28:48 EST

On Wed, Aug 13, 2014 at 12:57 AM, Alexei Starovoitov <ast@xxxxxxxxxxxx> 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").


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