Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Song Liu <songliubraving@fb.com>
To:     Namhyung Kim <namhyung@kernel.org>
CC:     Song Liu <song@kernel.org>,
        Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>, Martin Lau <kafai@fb.com>,
        Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: Add bpf_read_raw_record() helper
Thread-Topic: [PATCH bpf-next] bpf: Add bpf_read_raw_record() helper
Thread-Index: AQHYtzPeWFYcAGzsN0Wstq4jJDfNwK3AJloAgAAJpYCAAA9aAIAAO0MAgAAulQCAAAilAIAAsuMAgAAazgCAAAnxgIAADKuAgAAYuoA=
Date:   Fri, 26 Aug 2022 20:58:48 +0000
Message-ID: <FD49F694-10FA-4346-8303-E1E185C3E6E4@fb.com>
References: <20220823210354.1407473-1-namhyung@kernel.org>
 <CAEf4Bzbd0-jGFCSCJu3eDxxom42xnH9Tevq0n50-AajjHb5t3g@mail.gmail.com>
 <A9E2E766-E8A2-4E2E-A661-922400D2674D@fb.com>
 <CAEf4BzbGf6FuM7VcnA7HKb33HJeJjrDuydC4h1_tCUB8sPCW2g@mail.gmail.com>
 <E215461A-01E7-4677-A404-C4439D66A7AF@fb.com>
 <CAM9d7cgigkU8quUMpScL=Xt8+WLDVXKiF5xdKiz7BbDPibSNjg@mail.gmail.com>
 <CAPhsuW5V1U_UTHQw9E80vCTeP4Jqg9Ta8B+7o3pybKB=8CGRFA@mail.gmail.com>
 <CAM9d7cjTtOkRHLOosxHN8PcbVbhTK=uLDGjw8N5=1QiTHcd6rQ@mail.gmail.com>
 <C7F3F33B-4A8E-428C-9FED-FB635955C2B1@fb.com>
 <FCC75F8E-4C2F-42A4-B582-9BE3BB87E15A@fb.com>
 <CAM9d7cj6YNTL+u38PZjhPF2Qg_BYiJ1NMmDkPDx3N3Xe+ZTbyA@mail.gmail.com>
In-Reply-To: <CAM9d7cj6YNTL+u38PZjhPF2Qg_BYiJ1NMmDkPDx3N3Xe+ZTbyA@mail.gmail.com>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?6u/GQVURjFN3xbtGR1fjPIPtI3krgzoTQMx8Vhj4UqaBNFNbWt66K4LDl8qW?=
 =?us-ascii?Q?zF7RzdVA7pd0eY/hxFeTeaA8wsfi2fze8ojq8CRHvPv1dmnQBJy+n7FvRbYk?=
 =?us-ascii?Q?ie40LoE991wFJjQrTpT8TD2yaE4AJjhf3v5yY0iiza39Y0Y0RdRqCa5Bw+TJ?=
 =?us-ascii?Q?N3SKRufYcJKNxablezbNG+f8ULc2bqdNC8GnExEpeRl3Z1nUO7uuaJ6t7C52?=
 =?us-ascii?Q?mRYOwERzb+4hIgsvINh2LWxSyBvFm2hzEBzAcW73txj0ixQz7l6CLK/FcX3R?=
 =?us-ascii?Q?/V2BxHDqSjptIglJeMmllJFuXalD6MctMkyD6uasYXUi/n12X4bCp7lk+WSS?=
 =?us-ascii?Q?Mrc6GS1VEq3Am59bmOF5qzyTaS2KttkAORExfDSLjeg8MSX9oSF6yAo2pYS6?=
 =?us-ascii?Q?g6+1dDDb9iF5AbhRL5B5+1ZCJPOjcbRxb3RXP4HIga2kU/T9gIL4rjhgCaa4?=
 =?us-ascii?Q?VMqceLcyvKAlP8SauuMbYT6DiQTeJDmNSno6HY4iQSPeVEBtdBzboOc5sj8Q?=
 =?us-ascii?Q?aJ3BklV/4L/EVHLliV5vaQYKdEHNgqAUSAkd5Tnhufd+lNB9PSgPg1YBDSM3?=
 =?us-ascii?Q?8wxP78/k05FY2R0RE6n/7FHlMJF0sxxb9gu6Za9tyCWCxSVcPoTp76XjBuT7?=
 =?us-ascii?Q?XNNNHN/4wMAqGoa4pU6jwLtg61QHN4UZ1IQBfh6xJSJFsOVIy53dMcCZPX93?=
 =?us-ascii?Q?bZ9QqqaMdyWZgWWXMPZrY7kCpZDZ+L8IVzpVCVpxdk7xHfnZXpMLOL7JhEdl?=
 =?us-ascii?Q?F5XGG9YRAlevnzYnJalEYqH2X2pgjT2k/H/61EWFt7CQFnUwf6BQPva/vDU5?=
 =?us-ascii?Q?cw6hnRfiTj5q8kSMFjbJsr1aX8Cpe9sIZrwJ3GqhLFCdUNGhYM/NE9bxuPME?=
 =?us-ascii?Q?k6gW44h0PszsMKpw8lBXmDxc7yALm9oTyffnhzbpTfgmPhZLOfNVbc4qRbbY?=
 =?us-ascii?Q?aAXGVwJ2zpfto1FzZKJF0HAfhFJolJRn4I8Foj+SelWXgM5ldg1NH642QUxc?=
 =?us-ascii?Q?NpDDQE1X7DFpdNZqp3cV6IqC+QP4jY+t1loZlnAku9mmQlSNUXbmvuiPbM1L?=
 =?us-ascii?Q?gyEksk4KFfc2bc259WkHd8lCJcYxFYhNkJQj5Vn/8QBa2Pok6o/kWlBl42zi?=
 =?us-ascii?Q?S5J8VzvcWL/WOJ951AMltjHwtXwGkKZcH4ISKQdSstaWEKRZMW+KOBlrUvcB?=
 =?us-ascii?Q?nuQcgDwI1wi3EvhMc6V9NU7bCnCdaNL3wV+Ws2FeRD0UPDiu48p7fqrz8LQm?=
 =?us-ascii?Q?PkoyMRlprcyMNDQoc2UVGz4bnKK0mqHZGj8hHe2Vxw+yoYvXWHuMq/faeKqD?=
 =?us-ascii?Q?Eo9zwJGQNw7ST2RrMbGIcR1faF63rDC4mVSt+Wl74foKFkQx01SlkWcWemIP?=
 =?us-ascii?Q?N+GjFeWxjatj7t3kNrjRuCMp5JmLVps4Gq1IIWzBvHQOit6M7UEKcsHk1WJV?=
 =?us-ascii?Q?eoTKFnliR7VBJxkj2qc5SEhXTdh5yISv3j5XUJmI5BfkZJRXNQ6dVyDv+tcq?=
 =?us-ascii?Q?Ccmj8eSTqPcw8NNR1f9wOjcsgyeuuUAwPcXGBA8F2uzXrVelmRCJwReYmtZQ?=
 =?us-ascii?Q?HulVDedGN7+ap9A2k0z0ZOItq7NHWmfV8QQRhuvNKt+FCsBO3KXd9g/3+Swp?=
 =?us-ascii?Q?VNh99Z6FsP+26yNzqGJhc1I=3D?=
Content-Type: text/plain; charset="us-ascii"
Content-ID: <6D089AB07810C24D9E38596F890F64D8@namprd15.prod.outlook.com>
MIME-Version: 1.0
X-OriginatorOrg: fb.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: SA1PR15MB5109.namprd15.prod.outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: fd5d0881-60e4-498c-ab6c-08da87a5c5f6
X-MS-Exchange-CrossTenant-originalarrivaltime: 26 Aug 2022 20:58:48.6352
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: jvGqe3Fa93X+fzzY6kBaDXbtJVAU+RahE9X+RF9iDdtK7vwDCSvKLn51Sij7ECYUmBeocL+5qfqaF3lOmx54ow==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR15MB4395
X-Proofpoint-GUID: lKHw2aZi1xkt_AlvdI57yoqALavoGkcB
X-Proofpoint-ORIG-GUID: lKHw2aZi1xkt_AlvdI57yoqALavoGkcB
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.517,FMLib:17.11.122.1
 definitions=2022-08-26_12,2022-08-25_01,2022-06-22_01
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,
        RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,
        T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


> On Aug 26, 2022, at 12:30 PM, Namhyung Kim <namhyung@kernel.org> wrote:
> 
> On Fri, Aug 26, 2022 at 11:45 AM Song Liu <songliubraving@fb.com> wrote:
> 
>>> And actually, we can just read ctx->data and get the raw record,
>>> right..?
>> 
>> Played with this for a little bit. ctx->data appears to be not
>> reliable sometimes. I guess (not 100% sure) this is because we
>> call bpf program before event->orig_overflow_handler. We can
>> probably add a flag to specify we want to call orig_overflow_handler
>> first.
> 
> I'm not sure.  The sample_data should be provided by the caller
> of perf_event_overflow.  So I guess the bpf program should see
> a valid ctx->data.

Let's dig into this. Maybe we need some small changes in 
pe_prog_convert_ctx_access. 

> Also I want to control calling the orig_overflow_handler based
> on the return value of the BPF program.  So calling the orig
> handler before BPF won't work for me. :)

Interesting. Could you share more information about the use case?

Thanks,
Song