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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@kernel.org>
To:     shaozhengchao <shaozhengchao@huawei.com>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "daniel@iogearbox.net" <daniel@iogearbox.net>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "hawk@kernel.org" <hawk@kernel.org>,
        "john.fastabend@gmail.com" <john.fastabend@gmail.com>,
        "andrii@kernel.org" <andrii@kernel.org>,
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Cc:     "weiyongjun (A)" <weiyongjun1@huawei.com>,
        yuehaibing <yuehaibing@huawei.com>
Subject: Re: =?utf-8?B?562U5aSNOg==?= [PATCH bpf-next] samples/bpf: check
 detach prog exist or
 not in xdp_fwd
In-Reply-To: <f9c85578b94a4a38b3f7b9c796810a30@huawei.com>
References: <20220509005105.271089-1-shaozhengchao@huawei.com>
 <87pmknyr6b.fsf@toke.dk> <f9c85578b94a4a38b3f7b9c796810a30@huawei.com>
Date:   Mon, 09 May 2022 12:55:29 +0200
Message-ID: <87h75zynz2.fsf@toke.dk>
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shaozhengchao <shaozhengchao@huawei.com> writes:

> -----=E9=82=AE=E4=BB=B6=E5=8E=9F=E4=BB=B6-----
> =E5=8F=91=E4=BB=B6=E4=BA=BA: Toke H=C3=B8iland-J=C3=B8rgensen [mailto:tok=
e@kernel.org]=20
> =E5=8F=91=E9=80=81=E6=97=B6=E9=97=B4: 2022=E5=B9=B45=E6=9C=889=E6=97=A5 1=
7:46
> =E6=94=B6=E4=BB=B6=E4=BA=BA: shaozhengchao <shaozhengchao@huawei.com>; bp=
f@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; as=
t@kernel.org; daniel@iogearbox.net; davem@davemloft.net; kuba@kernel.org; h=
awk@kernel.org; john.fastabend@gmail.com; andrii@kernel.org; kafai@fb.com; =
songliubraving@fb.com; yhs@fb.com; kpsingh@kernel.org
> =E6=8A=84=E9=80=81: weiyongjun (A) <weiyongjun1@huawei.com>; shaozhengcha=
o <shaozhengchao@huawei.com>; yuehaibing <yuehaibing@huawei.com>
> =E4=B8=BB=E9=A2=98: Re: [PATCH bpf-next] samples/bpf: check detach prog e=
xist or not in xdp_fwd
>
> Zhengchao Shao <shaozhengchao@huawei.com> writes:
>
>> Before detach the prog, we should check detach prog exist or not.
>
> If we're adding such a check we should also check that it's the *right* p=
rogram. I.e., query the ID for the program name and check that it matches w=
hat the program attached, then obtain an fd and pass that as XDP_EXPECTED_F=
D on detach to make sure it wasn't swapped out in the meantime...
>
> -Toke
>
> Thank you for your reply. When finish running xdp_fwd to attatch prog,
> the program will exit and can't store fd as XDP_EXPECTED_FD.
>
> I think the sample xdp_fwd -d is just detach prog and don't care if
> the fd is expected.

So why are you adding the check? Either keep it the way it is, or add a
proper check that examines the program type; you're right that it
doesn't store the prog FD, but you can still check the program name and
see if it matches to get some idea that it's not a totally separate
program that's loaded. I think doing so would be an improvement to the
sample, but just adding a check if a program is loaded is not, really...

-Toke