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Date: Sat, 28 Mar 2015 23:16:36 +0100
From: Daniel Borkmann <daniel@iogearbox.net>
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To: Alexei Starovoitov <ast@plumgrid.com>, He Kuang <hekuang@huawei.com>
CC: wangnan0@huawei.com, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] bpf: Suggestion on bpf syscall interface
References: <55169240.7040103@huawei.com> <5516E32B.6030502@plumgrid.com>
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On 03/28/2015 06:21 PM, Alexei Starovoitov wrote:
> On 3/28/15 4:36 AM, He Kuang wrote:
>> Hi, Alexei
>>
>> In our end-end IO module project, we use bpf maps to record
>> configurations. According to current bpf syscall interface, we
>> should specify map_fd to lookup/update bpf maps, so we are
>> restricted to do config in the same user program.
>
> you can pass map_fd and prog_fd from one process to another via normal
> scm_rights mechanism.

+1, I've just tried that out in the context of a different work and
works like a charm.

>> My suggestion is to export this kind of operations to sysfs, so
>> we can load&attach bpf progs and config it seperately. We
>> implement this feature in our demo project. What's your opinion
>> on this?
>
> Eventually we may use single sysfs file for lsmod-like listings, but I
> definitely don't want to create parallel interface to maps via sysfs.

Yes, that would be a bad design decision. Btw, even more lightweight
for kernel-side would be to just implement .show_fdinfo() for the anon
indoes on the map/prog store and have some meta information exported
from there. You can then grab that via /proc/<pid>/fdinfo/<fd>, I
would consider such a thing a slow-path operation anyway, and you would
also get the app info using it for free.

> It's way too expensive and not really suitable for binary key/values.

+1