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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 CB1D2ECDFB1 for ; Fri, 13 Jul 2018 07:30:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 854B1208C4 for ; Fri, 13 Jul 2018 07:30:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 854B1208C4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1730644AbeGMHnt convert rfc822-to-8bit (ORCPT ); Fri, 13 Jul 2018 03:43:49 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:47858 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727231AbeGMHnt (ORCPT ); Fri, 13 Jul 2018 03:43:49 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CD1EF402382F; Fri, 13 Jul 2018 07:30:26 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-149.rdu2.redhat.com [10.10.120.149]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5274C1C67A; Fri, 13 Jul 2018 07:30:25 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <5A7CC3BF-5F4E-4624-A129-4BD0434D0747@amacapital.net> References: <5A7CC3BF-5F4E-4624-A129-4BD0434D0747@amacapital.net> <3236C75A-5D74-4BB4-A1EC-06F6E22D810C@amacapital.net> <611054C7-D6E8-4C89-958E-3128C9305E1E@amacapital.net> <20180712223223.GA28610@thunk.org> <153126248868.14533.9751473662727327569.stgit@warthog.procyon.org.uk> <153126264966.14533.3388004240803696769.stgit@warthog.procyon.org.uk> <686E805C-81F3-43D0-A096-50C644C57EE3@amacapital.net> <22370.1531293761@warthog.procyon.org.uk> <7002.1531407244@warthog.procyon.org.uk> <16699.1531426991@warthog.procyon.org.uk> <18233.1531430797@warthog.procyon.org.uk> <22105.1531436081@warthog.procyon.org.uk> <23894.1531438559@warthog.procyon.org.uk> <26064.1531440190@warthog.procyon.org.uk> To: Andy Lutomirski Cc: dhowells@redhat.com, "Theodore Y. Ts'o" , Linus Torvalds , Andrew Lutomirski , Al Viro , Linux API , linux-fsdevel , Linux Kernel Mailing List , Jann Horn Subject: Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9] MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3428.1531467024.1@warthog.procyon.org.uk> Content-Transfer-Encoding: 8BIT Date: Fri, 13 Jul 2018 08:30:24 +0100 Message-ID: <3429.1531467024@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Fri, 13 Jul 2018 07:30:26 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Fri, 13 Jul 2018 07:30:26 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'dhowells@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andy Lutomirski wrote: > > Also you can't currently directly create a bind mount from userspace as you > > can only bind from another path point - which you may not be able to access > > (either by permission failure or because it's not in your mount namespace). > > > > Are you trying to preserve the magic bind semantics with the new API? No, I'm pointing out that you can't emulate this by doing a bind mount from userspace if you can't access the thing you're binding from. Now, we could create a syscall that just picks up an extant superblock using a device and attaches it to a mount for you, but that would have to be at least partially parameterised - which would be very fs-dependent - so that it can know whether or not you're allowed to create another mount to that sb. What you're talking about is emulating sget() in userspace - when we have to do it in the kernel anyway if we still offer mount(2). David