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Sun, 19 Apr 2020 05:30:27 +0000 Subject: Re: [RFC PATCH bpf-next v2 00/17] bpf: implement bpf based dumping of kernel data structures To: Alan Maguire , David Ahern CC: Andrii Nakryiko , , Martin KaFai Lau , , Alexei Starovoitov , Daniel Borkmann , References: <20200415192740.4082659-1-yhs@fb.com> <40e427e2-5b15-e9aa-e2cb-42dc1b53d047@gmail.com> From: Yonghong Song Message-ID: <08d95e5f-9b14-4e61-8b71-f7be3b5cc30f@fb.com> Date: Sat, 18 Apr 2020 22:30:24 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: CO2PR04CA0170.namprd04.prod.outlook.com (2603:10b6:104:4::24) To MW3PR15MB3883.namprd15.prod.outlook.com (2603:10b6:303:51::22) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from wongal-imac.dhcp.thefacebook.com (2620:10d:c090:400::5:7ab3) by CO2PR04CA0170.namprd04.prod.outlook.com (2603:10b6:104:4::24) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2921.27 via Frontend Transport; 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For example, Martin wants to dump socket local >> >> If kernel support is needed for bpfdump of kernel data structures, you >> are not really solving the kernel support problem. i.e., to dump >> ipv4_route's you need to modify the relevant proc show function. >> > > I need to dig into this patchset a bit more, but if there is > a need for in-kernel BTF-based structure dumping I've got a > work-in-progress patchset that does this by generalizing the code > that deals with seq output in the verifier. I've posted it > as an RFC in case it has anything useful to offer here: > > https://lore.kernel.org/bpf/1587120160-3030-1-git-send-email-alan.maguire@oracle.com/T/#t > > The idea is that by using different callback function we can achieve > seq, snprintf or other output in-kernel using the kernel BTF data. > I created one consumer as a proof-of-concept; it's a printk pointer > format specifier. Since the dump format is determined in kernel > it's a bit constrained format-wise, but may be good enough for > some cases. The bpfdump work and here in-kernel btf dumping are different. The bpfdump BPF programs are triggered with a user syscall, e.g., cat /sys/kernel/bpfdump/task/my_dumper (also calling open()) or when user open() an anonymous dumper. The BPF program can "print" some data through bpf_seq_printf() helper. These printed data will be received by user space through read() syscall. Your work is greater as it makes kernel print more readable. There is no overlap between your work and bpfdump.