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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 D6C1CC55186 for ; Thu, 23 Apr 2020 00:48:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B198D2075A for ; Thu, 23 Apr 2020 00:48:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726050AbgDWAsR (ORCPT ); Wed, 22 Apr 2020 20:48:17 -0400 Received: from relay1-d.mail.gandi.net ([217.70.183.193]:2817 "EHLO relay1-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725846AbgDWAsR (ORCPT ); Wed, 22 Apr 2020 20:48:17 -0400 X-Originating-IP: 50.39.163.217 Received: from localhost (50-39-163-217.bvtn.or.frontiernet.net [50.39.163.217]) (Authenticated sender: josh@joshtriplett.org) by relay1-d.mail.gandi.net (Postfix) with ESMTPSA id 9A5F1240008; Thu, 23 Apr 2020 00:48:10 +0000 (UTC) Date: Wed, 22 Apr 2020 17:48:07 -0700 From: Josh Triplett To: Miklos Szeredi Cc: Michael Kerrisk , io-uring@vger.kernel.org, "linux-fsdevel@vger.kernel.org" , lkml , Alexander Viro , Arnd Bergmann , Jens Axboe , Aleksa Sarai , linux-man , Linux API Subject: Re: [PATCH v5 2/3] fs: openat2: Extend open_how to allow userspace-selected fds Message-ID: <20200423004807.GC161058@localhost> References: <9873b8bd7d14ff8cd2a5782b434b39f076679eeb.1587531463.git.josh@joshtriplett.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Wed, Apr 22, 2020 at 09:55:56AM +0200, Miklos Szeredi wrote: > On Wed, Apr 22, 2020 at 8:06 AM Michael Kerrisk (man-pages) > wrote: > > > > [CC += linux-api] > > > > On Wed, 22 Apr 2020 at 07:20, Josh Triplett wrote: > > > > > > Inspired by the X protocol's handling of XIDs, allow userspace to select > > > the file descriptor opened by openat2, so that it can use the resulting > > > file descriptor in subsequent system calls without waiting for the > > > response to openat2. > > > > > > In io_uring, this allows sequences like openat2/read/close without > > > waiting for the openat2 to complete. Multiple such sequences can > > > overlap, as long as each uses a distinct file descriptor. > > If this is primarily an io_uring feature, then why burden the normal > openat2 API with this? This feature was inspired by io_uring; it isn't exclusively of value with io_uring. (And io_uring doesn't normally change the semantics of syscalls.) > This would also allow Implementing a private fd table for io_uring. > I.e. add a flag interpreted by file ops (IORING_PRIVATE_FD), including > openat2 and freely use the private fd space without having to worry > about interactions with other parts of the system. I definitely don't want to add a special kind of file descriptor that doesn't work in normal syscalls taking file descriptors. A file descriptor allocated via O_SPECIFIC_FD is an entirely normal file descriptor, and works anywhere a file descriptor normally works.