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Fri, 27 Mar 2020 22:28:23 +0000 Subject: Re: [PATCH bpf-next v2] libbpf: Add getter for pointer to data area for internal maps To: =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , Andrii Nakryiko CC: Daniel Borkmann , bpf , Networking References: <20200326151741.125427-1-toke@redhat.com> <20200327125818.155522-1-toke@redhat.com> <87tv29l9ia.fsf@toke.dk> From: Alexei Starovoitov Message-ID: Date: Fri, 27 Mar 2020 15:28:20 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 In-Reply-To: <87tv29l9ia.fsf@toke.dk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: CO2PR07CA0046.namprd07.prod.outlook.com (2603:10b6:100::14) To MW3PR15MB3772.namprd15.prod.outlook.com (2603:10b6:303:4c::14) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21c1::129f] (2620:10d:c090:400::5:4ef7) by CO2PR07CA0046.namprd07.prod.outlook.com (2603:10b6:100::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2856.19 via Frontend Transport; Fri, 27 Mar 2020 22:28:22 +0000 X-Originating-IP: [2620:10d:c090:400::5:4ef7] X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 0958c873-c105-498f-dfd1-08d7d29e2901 X-MS-TrafficTypeDiagnostic: MW3PR15MB3994: X-Microsoft-Antispam-PRVS: X-FB-Source: Internal X-MS-Oob-TLC-OOBClassifiers: OLM:7219; X-Forefront-PRVS: 0355F3A3AE X-Forefront-Antispam-Report: SFV:NSPM;SFS:(10019020)(366004)(39860400002)(376002)(396003)(346002)(136003)(316002)(36756003)(31686004)(52116002)(66946007)(66574012)(110136005)(2906002)(66556008)(54906003)(66476007)(5660300002)(4326008)(478600001)(6486002)(53546011)(81166006)(81156014)(86362001)(31696002)(186003)(2616005)(8676002)(8936002)(16526019);DIR:OUT;SFP:1102;SCL:1;SRVR:MW3PR15MB3994;H:MW3PR15MB3772.namprd15.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords; Received-SPF: None (protection.outlook.com: fb.com does not designate permitted sender hosts) X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: hni8VtF5q4sV3zddR3vuj2IcfX5IbGFHMpGFP60sxvltAPNgWFl5rv/gjywLbrmbIVDys6SUVxuy4i8kFIoYi1p2StIa9HhsHm1vUPx45TxOmMISwK+guCnkdioABRa/KK3aXBPg7z6swYQv6AM+6ln3z5B8xazovOHNIzD21tDndbB9TBiSC/pWei6EPp5eFer6T+qqXYjXeELQxz2mLQWkNP51CkVU40DEQkcHus2bFLFqJ5uOXmcsfHRp6t+8/mvpKOuckXwtlnowGg6D+oTxp81XmmOwfsL9L1zTguAAFc9lhriwZeD6zov7+AhcfZpQNBs2QbOWsxxCRI612SZgFZ1qddqllEJ8hvJu751lkeDms0WN+ltOoChZfDq0gDYSjeHEwhBtlYbsulqNlzMswWvrndngvUixRYAiH87xFOQ9BhrF0Ya+AsLtBA6y X-MS-Exchange-AntiSpam-MessageData: HNUnegBe1BRSvoXbNh5s6uDCna6kK02unm+QKqK8+F0rouL15/LRs3rKFyeds3EYhRn0uChKj9gYaHEnT9kbQ8aefCYGFpqhi3S7fzdzy+l+CbTVla/L4Y9TV11aF20lMjpuxcKYElE2NM2hl8MH4ylxUZy2Va+IXZigWhTSHaiYdMusGz6pOxJO4pjg9+kV X-MS-Exchange-CrossTenant-Network-Message-Id: 0958c873-c105-498f-dfd1-08d7d29e2901 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Mar 2020 22:28:23.2671 (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: oEOE0ZDasBly0lV+3Eezw1Q//JkTUyGs8r1i7DG4qEzgsLlGYQ8RwyBblfLZ/1T+ X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR15MB3994 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.645 definitions=2020-03-27_09:2020-03-27,2020-03-27 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 bulkscore=0 spamscore=0 clxscore=1015 mlxlogscore=999 priorityscore=1501 lowpriorityscore=0 phishscore=0 adultscore=0 impostorscore=0 suspectscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003270185 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 3/27/20 3:26 PM, Toke Høiland-Jørgensen wrote: > Andrii Nakryiko writes: > >> On Fri, Mar 27, 2020 at 5:58 AM Toke Høiland-Jørgensen wrote: >>> >>> For internal maps (most notably the maps backing global variables), libbpf >>> uses an internal mmaped area to store the data after opening the object. >>> This data is subsequently copied into the kernel map when the object is >>> loaded. >>> >>> This adds a getter for the pointer to that internal data store. This can be >>> used to modify the data before it is loaded into the kernel, which is >>> especially relevant for RODATA, which is frozen on load. This same pointer >>> is already exposed to the auto-generated skeletons, so access to it is >>> already API; this just adds a way to get at it without pulling in the full >>> skeleton infrastructure. >>> >>> Signed-off-by: Toke Høiland-Jørgensen >>> --- >>> v2: >>> - Add per-map getter for data area instead of a global rodata getter for bpf_obj >>> >>> tools/lib/bpf/libbpf.c | 9 +++++++++ >>> tools/lib/bpf/libbpf.h | 1 + >>> tools/lib/bpf/libbpf.map | 1 + >>> 3 files changed, 11 insertions(+) >>> >>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c >>> index 085e41f9b68e..a0055f8908fd 100644 >>> --- a/tools/lib/bpf/libbpf.c >>> +++ b/tools/lib/bpf/libbpf.c >>> @@ -6756,6 +6756,15 @@ void *bpf_map__priv(const struct bpf_map *map) >>> return map ? map->priv : ERR_PTR(-EINVAL); >>> } >>> >>> +void *bpf_map__data_area(const struct bpf_map *map, size_t *size) >> >> I'm not entirely thrilled about "data_area" name. This is entirely for >> providing initial value for maps, so maybe something like >> bpf_map__init_value() or something along those lines? >> >> Actually, how about a different API altogether: >> >> bpf_map__set_init_value(struct bpf_map *map, void *data, size_t size)? >> >> Application will have to prepare data of correct size, which will be >> copied to libbpf's internal storage. It also doesn't expose any of >> internal pointer. I don't think extra memcopy is a big deal here. >> Thoughts? > > Huh, yeah, that's way better. Why didn't I think of that? Think maybe I > was too focused on doing this the same way the skeleton code is. I'll > send a v3 :) Could you please add a selftest as well? I'm not excited about new features without tests.