From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932744AbdEXSBw (ORCPT ); Wed, 24 May 2017 14:01:52 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:56933 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754408AbdEXSBt (ORCPT ); Wed, 24 May 2017 14:01:49 -0400 Authentication-Results: kernel.org; dkim=none (message not signed) header.d=none;kernel.org; dmarc=none action=none header.from=fb.com; Date: Wed, 24 May 2017 11:01:07 -0700 From: Shaohua Li To: Tejun Heo CC: Christoph Hellwig , , , , Subject: Re: [PATCH 5/5] kernfs: add exportfs operations Message-ID: <20170524180106.GA85439@evv-mbp.dhcp.thefacebook.com> References: <3d3a0860317afa0fb722c1a6df58e04593fc700a.1495490800.git.shli@fb.com> <20170523074019.GC29525@infradead.org> <20170523185711.GB13222@htj.duckdns.org> <20170524173822.GB13151@infradead.org> <20170524173939.GJ24798@htj.duckdns.org> <20170524174138.GA28155@infradead.org> <20170524174604.GK24798@htj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; 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So maybe you just need > > to send the full patch so that reviewers get the full picture. > > Here's a simple scenario. Let's say blktrace now exposes the cgroup > inode and generation numbers per trace. Userland tool now wants to > show that in a human readable format but it can only map back the > inode and generation numbers to the path by scanning the cgroup tree. > So, the goal is having a token which is not path which uniquely > identifies a cgroup and the ability to map that back to cgroup path. > We can add a dedicated interface to cgroup root, for example, and > allow querying by echoing inode and generation numbers into it but > that's kinda clumsy. blktrace is the target I'm working on, because we can't use pid to determine where a bio comes from, so we show an ID. Userspace tool can use the ID to find the cgroup path. Or an BPF program can use the ID to filter trace. Regardless how we implement the ID, it should be something like an inode number and generation number. And since we already had existing syscall to map between fhandle and path, I choose the exportfs operations. I'll post a full patch set later. Thanks, Shaohua