netdev - Re: [PATCH bpf-next 3/3] libbpf: Add pin option to automount BPF filesystem before pinning

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Message-ID: <87o8y7n8ia.fsf@toke.dk>
Date:   Wed, 23 Oct 2019 10:58:21 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        David Miller <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 3/3] libbpf: Add pin option to automount BPF filesystem before pinning

Andrii Nakryiko <andrii.nakryiko@...il.com> writes:

> On Tue, Oct 22, 2019 at 12:04 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
>>
>> > On Tue, Oct 22, 2019 at 9:08 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>> >>
>> >> From: Toke Høiland-Jørgensen <toke@...hat.com>
>> >>
>> >> While the current map pinning functions will check whether the pin path is
>> >> contained on a BPF filesystem, it does not offer any options to mount the
>> >> file system if it doesn't exist. Since we now have pinning options, add a
>> >> new one to automount a BPF filesystem at the pinning path if that is not
>> >
>> > Next thing we'll be adding extra options to mount BPF FS... Can we
>> > leave the task of auto-mounting BPF FS to tools/applications?
>>
>> Well, there was a reason I put this into a separate patch: I wasn't sure
>> it really fit here. My reasoning is the following: If we end up with a
>> default auto-pinning that works really well, people are going to just
>> use that. And end up really confused when bpffs is not mounted. And it
>> seems kinda silly to make every application re-implement the same mount
>> check and logic.
>>
>> Or to put it another way: If we agree that the reasonable default thing
>> is to just pin things in /sys/fs/bpf, let's make it as easy as possible
>> for applications to do that right.
>>
>
> This reminds me the setrlimit() issue, though.

Heh, yeah. I personally consider the rlimit issue one of the top
usability issues with BPF :/

> And we decided that library shouldn't be manipulating global resources
> on behalf of users. I think this is a similar one.

Hmm, that's a fair point, actually. I do get twitchy watching most
applications just blindly setting rlimit to unlimited before they try to
load BPF programs...

I think I'll just drop this patch for now :)

-Toke