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To: Andrii Nakryiko , Alexei Starovoitov CC: "David S. Miller" , Daniel Borkmann , Andrii Nakryiko , john fastabend , bpf , Kernel Team References: <20210512213256.31203-1-alexei.starovoitov@gmail.com> <20210512213256.31203-17-alexei.starovoitov@gmail.com> From: Alexei Starovoitov Message-ID: Date: Thu, 13 May 2021 15:22:39 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:f822] X-ClientProxiedBy: MWHPR2001CA0006.namprd20.prod.outlook.com (2603:10b6:301:15::16) To BN8PR15MB3282.namprd15.prod.outlook.com (2603:10b6:408:a8::32) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21d6::1acd] (2620:10d:c090:400::5:f822) by MWHPR2001CA0006.namprd20.prod.outlook.com (2603:10b6:301:15::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4087.50 via Frontend Transport; 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Note only mmaped maps qualify. >> Just as bpf_map__set_initial_value() works only for mmaped kconfig. > > This sentence is confusing. bpf_map__set_initial_value() rejects > LIBBPF_MAP_KCONFIG, so it *doesn't* work for kconfig. But your > implementation will return non-NULL pointer for kconfig (it will be > all zeroes before load). So did you intend to match > set_initial_value() semantics or not? Good catch. I'll reword. It was too forward looking and ended up as completely incorrect sentence. The idea was to make getter work for all is_internal and mmaped maps (including kconfig), so that after __open and before __load phase can populate them with correct values. Initially for kconfig I was thinking to do it as part of the loader program, but the kernel doesn't have in memory kconfig. Unzipping and string searching didn't feel like the right task for the loader prog/kernel, so the light skel instead will populate it from user space during __open. At that point we can either fail the __open if /proc/config.gz cannot be open or it doesn't have the fields the prog is looking for or proceed with default values in kconfig map that libbpf populated earlier during light skel and loader prog generation. Depending on that choice the bpf_map__initial_value() should either return initial value for kconfig or not. I think returning it for kconfig map doesn't hurt.