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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next v2 3/6] bpf: support attaching freplace programs to multiple attach points
Date: Mon, 20 Jul 2020 15:57:27 -0700	[thread overview]
Message-ID: <20200720225727.zs7x63u3f3kw3apt@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <87imemct2d.fsf@toke.dk>

On Fri, Jul 17, 2020 at 12:52:10PM +0200, Toke Høiland-Jørgensen wrote:
> 
> > It's a circular reference, obviously.
> > Need to think through the complications and locking.
> 
> Yup, will do so when I get back to this. One other implication of this
> change: If we make the linked_prog completely dynamic you can no longer
> do:
> 
> link_fd = bpf_raw_tracepoint_open(prog);
> close(link_fd);
> link_fd = bpf_raw_tracepoint_open(prog):
> 
> since after that close(), the original linked_prog will be gone. Unless
> we always leave at least one linked_prog alive? But then we can't
> guarantee that it's the target that was supplied on program load if it
> was reattached. Is that acceptable?

I think both options are fine.
We can start with simple case where close would destroy the last link
and if somebody complains we can keep 'at least one alive'.
This is such low level implementation detail that I don't think any user
can reliably count on it staying this way.

  reply	other threads:[~2020-07-20 22:57 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-15 13:08 [PATCH bpf-next v2 0/6] bpf: Support multi-attach for freplace programs Toke Høiland-Jørgensen
2020-07-15 13:09 ` [PATCH bpf-next v2 1/6] bpf: change logging calls from verbose() to bpf_log() and use log pointer Toke Høiland-Jørgensen
2020-07-16 10:10   ` Dan Carpenter
2020-07-16 10:10     ` Dan Carpenter
2020-07-16 10:10     ` Dan Carpenter
2020-07-15 13:09 ` [PATCH bpf-next v2 2/6] bpf: verifier: refactor check_attach_btf_id() Toke Høiland-Jørgensen
2020-07-15 13:09 ` [PATCH bpf-next v2 3/6] bpf: support attaching freplace programs to multiple attach points Toke Høiland-Jørgensen
2020-07-15 20:44   ` Alexei Starovoitov
2020-07-16 10:50     ` Toke Høiland-Jørgensen
2020-07-17  2:05       ` Alexei Starovoitov
2020-07-17 10:52         ` Toke Høiland-Jørgensen
2020-07-20 22:57           ` Alexei Starovoitov [this message]
2020-07-20  5:02         ` Andrii Nakryiko
2020-07-20 23:34           ` Alexei Starovoitov
2020-07-21  3:48             ` Andrii Nakryiko
2020-07-22  0:29               ` Alexei Starovoitov
2020-07-22  6:02                 ` Andrii Nakryiko
2020-07-23  0:32                   ` Alexei Starovoitov
2020-07-23  0:56                     ` Andrii Nakryiko
2020-07-16 10:14   ` Dan Carpenter
2020-07-16 10:14     ` Dan Carpenter
2020-07-16 10:14     ` Dan Carpenter
2020-07-15 13:09 ` [PATCH bpf-next v2 4/6] tools: add new members to bpf_attr.raw_tracepoint in bpf.h Toke Høiland-Jørgensen
2020-07-15 13:09 ` [PATCH bpf-next v2 5/6] libbpf: add support for supplying target to bpf_raw_tracepoint_open() Toke Høiland-Jørgensen
2020-07-15 13:09 ` [PATCH bpf-next v2 6/6] selftests: add test for multiple attachments of freplace program Toke Høiland-Jørgensen
2020-07-15 20:59 [PATCH bpf-next v2 3/6] bpf: support attaching freplace programs to multiple attach points kernel test robot

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