Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <afd9317561b1823da2fa473f29723da83247767e.camel@chromium.org>
Subject: Re: [PATCH bpf-next v2 1/3] bpf: Expose bpf_get_socket_cookie to
 tracing programs
From:   Florent Revest <revest@chromium.org>
To:     Martin KaFai Lau <kafai@fb.com>
Cc:     bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
        andrii@kernel.org, kpsingh@chromium.org, revest@google.com,
        linux-kernel@vger.kernel.org
Date:   Tue, 08 Dec 2020 20:40:08 +0100
In-Reply-To: <20201204194748.cqyz7hfx5s5dyszc@kafai-mbp.dhcp.thefacebook.com>
References: <20201203213330.1657666-1-revest@google.com>
         <20201204194748.cqyz7hfx5s5dyszc@kafai-mbp.dhcp.thefacebook.com>
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.36.4-2 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

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 ?