From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48C13ECAC25 for ; Thu, 12 Jul 2018 19:08:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 034E8208E9 for ; Thu, 12 Jul 2018 19:08:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 034E8208E9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732189AbeGLTTh (ORCPT ); Thu, 12 Jul 2018 15:19:37 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:48638 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727082AbeGLTTh (ORCPT ); Thu, 12 Jul 2018 15:19:37 -0400 Received: from localhost (LFbn-1-12247-202.w90-92.abo.wanadoo.fr [90.92.61.202]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 0D60C2C; Thu, 12 Jul 2018 19:08:44 +0000 (UTC) Date: Thu, 12 Jul 2018 21:08:42 +0200 From: Greg KH To: Andy Lutomirski Cc: Al Viro , David Howells , linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9] Message-ID: <20180712190842.GA2000@kroah.com> References: <153126248868.14533.9751473662727327569.stgit@warthog.procyon.org.uk> <153126264966.14533.3388004240803696769.stgit@warthog.procyon.org.uk> <20180712171505.GA23780@kroah.com> <20180712172024.GZ30522@ZenIV.linux.org.uk> <20180712180304.GA27758@kroah.com> <76211EBC-05ED-4FBA-A136-F5EEBFDD9FDF@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <76211EBC-05ED-4FBA-A136-F5EEBFDD9FDF@amacapital.net> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 12, 2018 at 11:30:32AM -0700, Andy Lutomirski wrote: > > > On Jul 12, 2018, at 11:03 AM, Greg KH wrote: > > > >> On Thu, Jul 12, 2018 at 06:20:24PM +0100, Al Viro wrote: > >>> On Thu, Jul 12, 2018 at 07:15:05PM +0200, Greg KH wrote: > >>>> On Tue, Jul 10, 2018 at 11:44:09PM +0100, David Howells wrote: > >>>> Provide an fsopen() system call that starts the process of preparing to > >>>> create a superblock that will then be mountable, using an fd as a context > >>>> handle. fsopen() is given the name of the filesystem that will be used: > >>>> > >>>> int mfd = fsopen(const char *fsname, unsigned int flags); > >>>> > >>>> where flags can be 0 or FSOPEN_CLOEXEC. > >>>> > >>>> For example: > >>>> > >>>> sfd = fsopen("ext4", FSOPEN_CLOEXEC); > >>>> write(sfd, "s /dev/sdb1"); // note I'm ignoring write's length arg > >>>> write(sfd, "o noatime"); > >>>> write(sfd, "o acl"); > >>>> write(sfd, "o user_attr"); > >>>> write(sfd, "o iversion"); > >>>> write(sfd, "o "); > >>>> write(sfd, "r /my/container"); // root inside the fs > >>>> write(sfd, "x create"); // create the superblock > >>> > >>> Ugh, creating configfs again in a syscall form? I know people love > >>> file descriptors, but can't you do this with a configfs entry instead if > >>> you really want to do this type of thing from userspace in this type of > >>> "style"? > >>> > >>> Why reinvent the wheel again? > >> > >> The damn thing REALLY, REALLY depends upon the fs type. How would > >> you map it on configfs? > > > > /sys/kernel/config/fs/ext4/ would work, right? Each fs "type" would be > > listed there. > > > > Anyway, the whole "write a bunch of options and then do a 'create'" is > > exactly the way configfs works. Why not use that? > > > > > > How do you mount configfs in the first place? And how do you use this > in a mount namespace without a private configfs instance or where you > don’t want configfs mounted?-- Ok, fair enough, I missed the part where this is going to replace mount(2). Although you could just use mount(2) to mount configfs on a mount point in the initramfs image and then go from there at boot time :) /me runs away...