linux-kernel - Re: [PATCH bpf-next v2 1/3] bpf: Expose bpf_get_socket

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Date:   Tue, 08 Dec 2020 20:40:08 +0100
From:   Florent Revest <revest@...omium.org>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kpsingh@...omium.org, revest@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 1/3] bpf: Expose bpf_get_socket_cookie to
 tracing programs

On Fri, 2020-12-04 at 11:47 -0800, Martin KaFai Lau wrote:
> On Thu, Dec 03, 2020 at 10:33:28PM +0100, Florent Revest wrote:
> > +const struct bpf_func_proto
> > bpf_get_socket_cookie_sock_tracing_proto = {
> > +	.func		= bpf_get_socket_cookie_sock,
> > +	.gpl_only	= false,
> > +	.ret_type	= RET_INTEGER,
> > +	.arg1_type      = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
> 
> In tracing where it gets a sk pointer, the sk could be NULL.
> A NULL check is required in the helper. Please refer to
> bpf_skc_to_tcp_sock[_proto] as an example.

Ah, good catch! :) 

> This proto is in general also useful for non tracing context where
> it can get a hold of a sk pointer. (e.g. another similar usage that
> will have a hold on a sk pointer for BPF_PROG_TYPE_SK_REUSEPORT [0]).

Agreed.

> In case if you don't need sleepable at this point as Daniel
> mentioned in another thread.  Does it make sense to rename this
> proto to something like bpf_get_socket_pointer_cookie_proto?

My understanding is that I could have two helpers definitions and
protos, one calling sock_gen_cookie and the other one calling
__sock_gen_cookie. Then I could just use:

return prog->aux->sleepable
       ? bpf_get_socket_pointer_cookie_sleepable_proto
       : bpf_get_socket_pointer_cookie_proto;

Would that work ?