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 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 18BABC6778F for ; Fri, 27 Jul 2018 21:51:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CA6C520842 for ; Fri, 27 Jul 2018 21:51:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CA6C520842 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 S2389876AbeG0XPc convert rfc822-to-8bit (ORCPT ); Fri, 27 Jul 2018 19:15:32 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35534 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2389804AbeG0XPb (ORCPT ); Fri, 27 Jul 2018 19:15:31 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2FFA77DAC3; Fri, 27 Jul 2018 21:51:42 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-116.rdu2.redhat.com [10.10.120.116]) by smtp.corp.redhat.com (Postfix) with ESMTP id 333FA111AF20; Fri, 27 Jul 2018 21:51:41 +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: References: <153271267980.9458.7640156373438016898.stgit@warthog.procyon.org.uk> <153271287586.9458.6001928723332685410.stgit@warthog.procyon.org.uk> To: Andy Lutomirski Cc: dhowells@redhat.com, Al Viro , Linux API , Linus Torvalds , Linux FS Devel , LKML Subject: Re: [PATCH 29/38] vfs: syscall: Add fsconfig() for configuring and managing a context [ver #10] MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <7033.1532728300.1@warthog.procyon.org.uk> Content-Transfer-Encoding: 8BIT Date: Fri, 27 Jul 2018 22:51:40 +0100 Message-ID: <7034.1532728300@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 27 Jul 2018 21:51:42 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 27 Jul 2018 21:51:42 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.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: > Unless I'm rather confused, you have two or possibly three ways to > pass in an open fd. Can you clarify what the difference is and/or > remove all but one of them? No, they're not equivalent. > > (*) fsconfig_set_path: A non-empty path is specified. The parameter must > > be expecting a path object. value points to a NUL-terminated string > > that is the path and aux is a file descriptor at which to start a > > relative lookup or AT_FDCWD. So, an example: fsconfig(fd, fsconfig_set_path, "source", "/dev/sda1", AT_FDCWD); I don't want to require that the caller open /dev/sda1 and pass in an fd as that might prevent the filesystem from "holding" it exclusively. > > (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH > > implied. You can't do: fsconfig(fd, fsconfig_set_path, "source", "", dir_fd); because AT_EMPTY_PATH cannot be specified directly[*]. What you do instead is: fsconfig(fd, fsconfig_set_path_empty, "source", "", dir_fd); [*] Not without a 6-arg syscall or some other way of passing it. I *could* require that the caller must call open(O_PATH) or openat(O_PATH) before calling fsconfig() - so you don't pass a string, but only a path-fd. > > (*) fsconfig_set_fd: An open file descriptor is specified. value must > > be NULL and aux indicates the file descriptor. See fd=%u on fuse. I think it's cleaner to do: fsconfig(fd, fsconfig_set_fd, "source", NULL, control_fd); saying explicitly that there's an open file to be passed rather than: fsconfig(fd, fsconfig_set_path, "source", NULL, control_fd); which indicates that you are actually providing a path. David