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Fri, 10 Apr 2020 22:43:01 +0000 Subject: Re: [RFC PATCH bpf-next 05/16] bpf: create file or anonymous dumpers To: Alexei Starovoitov CC: Andrii Nakryiko , , Martin KaFai Lau , , Alexei Starovoitov , Daniel Borkmann , References: <20200408232520.2675265-1-yhs@fb.com> <20200408232526.2675664-1-yhs@fb.com> <20200410030017.errh35srmbmd7uk5@ast-mbp.dhcp.thefacebook.com> From: Yonghong Song Message-ID: Date: Fri, 10 Apr 2020 15:42:42 -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: <20200410030017.errh35srmbmd7uk5@ast-mbp.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MWHPR22CA0044.namprd22.prod.outlook.com (2603:10b6:300:69::30) To MW3PR15MB3883.namprd15.prod.outlook.com (2603:10b6:303:51::22) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from MacBook-Pro-52.local (2620:10d:c090:400::5:e0e4) by MWHPR22CA0044.namprd22.prod.outlook.com (2603:10b6:300:69::30) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2900.15 via Frontend Transport; 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X-Microsoft-Antispam-Message-Info: aOKoFIS+W/hlKnW6E1nUI/ffCBwge1V0q7ExtTl1NAD0QBgo8IIOO2o1yCpJlmAFAFbAyZUQUDzl0kpUvJTX9D4xmIyKKBQLe+Xm40Qr09pu/+GEEl2a3Kr6UFitwfsOTFgewx2GN1oLhlaOKesUZpWWDU3WVHCiJNRA+0Wqio7ahYkwp35FbNT1p4i+AXmDyMMrCASlCOqUvY7OHIh2t6+ctzfrI+Tf0jpEqabL5OXsrmlz2zIcVtKCxAIyXIObtFm2gc5dQd555BjWi7dfGTNxmHShyxDU6UFgRGH2815GqJnksW9l7T9amgO3YiTj45nRnPgrqhbRA+fd5U3tAfd2cpWVmeCG/gRl9j3HbgUJ2Q66DrGpHJE21ynnhFYNv0tPDLbl1vnwz0q6HkYPOovmoIrwF5PDsom6dWMhM7T9MtmC+SawnQVfW/Sw8NyP X-MS-Exchange-AntiSpam-MessageData: gxt5AKghxVUAYM+zBJ+ZWNLAuXY65Tm6huxQZY5Yp5WBCxMidUAc7x53mlklZG9y7Ly3ivk1XmFuIAuyspXRcGPUWj1yuu4PF77quyd2QsrRCfqzPtc29HUHhYklvcsqyBgJVuh9u3gjKysxc/b96djnfdIe5wHwYooAwgqLrrr7wJpt5dIYi+d57xjRqyB1 X-MS-Exchange-CrossTenant-Network-Message-Id: e01b2d4c-bf99-458b-0e43-08d7dda0860f X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Apr 2020 22:43:01.2263 (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: KiMyqLYgpldwkxsc6UvBolBPKgf2DVDp2mPUtBMVYAjycf+oXKcjvK4oNO98hRaH X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR15MB3977 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.676 definitions=2020-04-10_10:2020-04-09,2020-04-10 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 phishscore=0 mlxscore=0 priorityscore=1501 malwarescore=0 suspectscore=0 adultscore=0 lowpriorityscore=0 spamscore=0 bulkscore=0 clxscore=1015 mlxlogscore=999 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004100160 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 4/9/20 8:00 PM, Alexei Starovoitov wrote: > On Wed, Apr 08, 2020 at 04:25:26PM -0700, Yonghong Song wrote: >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >> index 0f1cbed446c1..b51d56fc77f9 100644 >> --- a/include/uapi/linux/bpf.h >> +++ b/include/uapi/linux/bpf.h >> @@ -354,6 +354,7 @@ enum { >> /* Flags for accessing BPF object from syscall side. */ >> BPF_F_RDONLY = (1U << 3), >> BPF_F_WRONLY = (1U << 4), >> + BPF_F_DUMP = (1U << 5), > ... >> static int bpf_obj_pin(const union bpf_attr *attr) >> { >> - if (CHECK_ATTR(BPF_OBJ) || attr->file_flags != 0) >> + if (CHECK_ATTR(BPF_OBJ) || attr->file_flags & ~BPF_F_DUMP) >> return -EINVAL; >> >> + if (attr->file_flags == BPF_F_DUMP) >> + return bpf_dump_create(attr->bpf_fd, >> + u64_to_user_ptr(attr->dumper_name)); >> + >> return bpf_obj_pin_user(attr->bpf_fd, u64_to_user_ptr(attr->pathname)); >> } > > I think kernel can be a bit smarter here. There is no need for user space > to pass BPF_F_DUMP flag to kernel just to differentiate the pinning. > Can prog attach type be used instead? Think again. I think a flag is still useful. Suppose that we have the following scenario: - the current directory /sys/fs/bpf/ - user says pin a tracing/dump (target task) prog to "p1" It is not really clear whether user wants to pin to /sys/fs/bpf/p1 or user wants to pin to /sys/kernel/bpfdump/task/p1 unless we say that a tracing/dump program cannot pin to /sys/fs/bpf which seems unnecessary restriction. What do you think?