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_HELO_NONE,SPF_PASS 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 6D28FC2BA16 for ; Sat, 4 Apr 2020 05:58:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4AB47206CC for ; Sat, 4 Apr 2020 05:58:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725730AbgDDF6G (ORCPT ); Sat, 4 Apr 2020 01:58:06 -0400 Received: from relay1-d.mail.gandi.net ([217.70.183.193]:42923 "EHLO relay1-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725536AbgDDF6G (ORCPT ); Sat, 4 Apr 2020 01:58:06 -0400 X-Originating-IP: 50.39.173.183 Received: from localhost (50-39-173-183.bvtn.or.frontiernet.net [50.39.173.183]) (Authenticated sender: josh@joshtriplett.org) by relay1-d.mail.gandi.net (Postfix) with ESMTPSA id A1348240005; Sat, 4 Apr 2020 05:58:02 +0000 (UTC) Date: Fri, 3 Apr 2020 22:57:50 -0700 From: Josh Triplett To: io-uring@vger.kernel.org Cc: Jens Axboe Subject: [PATCH v3 0/3] Support userspace-selected fds Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org (Note: numbering this updated version v3, to avoid confusion with Jens' v2 that built on my v1. Jens, if you like this approach, please feel free to stack your additional patches from the io_uring-fd-select branch atop this series. 5.8 material, not intended for the current merge window.) This new version has an API to atomically increase the minimum fd and return the previous minimum, rather than just getting and setting the minimum; this makes it easier to allocate a range. (A library that might initialize after the program has already opened other file descriptors may need to check for existing open fds in the range after reserving it, and reserve more fds if needed; this can be done entirely in userspace, and we can't really do anything simpler in the kernel due to limitations on file-descriptor semantics, so this patch series avoids introducing any extra complexity in the kernel.) This new version also supports a __get_specific_unused_fd_flags call which accepts the limit for RLIMIT_NOFILE as an argument, analogous to __get_unused_fd_flags, since io_uring needs that to correctly handle RLIMIT_NOFILE. Inspired by the X protocol's handling of XIDs, allow userspace to select the file descriptor opened by a call like openat2, so that it can use the resulting file descriptor in subsequent system calls without waiting for the response the initial openat2 syscall. The first patch is independent of the other two; it allows reserving file descriptors below a certain minimum for userspace-selected fd allocation only. The second patch implements userspace-selected fd allocation for openat2, introducing a new O_SPECIFIC_FD flag and an fd field in struct open_how. 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. The third patch adds userspace-selected fd allocation to pipe2 as well. I did this partly as a demonstration of how simple it is to wire up O_SPECIFIC_FD support for a new fd-allocating system call, and partly in the hopes that this may make it more useful to wire up io_uring support for pipe2 in the future. Josh Triplett (3): fs: Support setting a minimum fd for "lowest available fd" allocation fs: openat2: Extend open_how to allow userspace-selected fds fs: pipe2: Support O_SPECIFIC_FD fs/fcntl.c | 2 +- fs/file.c | 62 ++++++++++++++++++++++++++++---- fs/io_uring.c | 3 +- fs/open.c | 6 ++-- fs/pipe.c | 16 ++++++--- include/linux/fcntl.h | 5 +-- include/linux/fdtable.h | 1 + include/linux/file.h | 4 +++ include/uapi/asm-generic/fcntl.h | 4 +++ include/uapi/linux/openat2.h | 2 ++ include/uapi/linux/prctl.h | 3 ++ kernel/sys.c | 5 +++ 12 files changed, 97 insertions(+), 16 deletions(-) -- 2.26.0