From patchwork Mon Aug 31 13:45:48 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 11746381 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0BD7913B1 for ; Mon, 31 Aug 2020 13:48:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E8DFF208CA for ; Mon, 31 Aug 2020 13:48:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727861AbgHaNry (ORCPT ); Mon, 31 Aug 2020 09:47:54 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:43642 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727783AbgHaNr3 (ORCPT ); Mon, 31 Aug 2020 09:47:29 -0400 Received: from ip5f5af70b.dynamic.kabel-deutschland.de ([95.90.247.11] helo=wittgenstein.fritz.box) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1kCk8y-00062w-R6; Mon, 31 Aug 2020 13:46:44 +0000 From: Christian Brauner To: linux-kernel@vger.kernel.org Cc: Christian Brauner , "Peter Zijlstra (Intel)" , Ingo Molnar , Thomas Gleixner , Oleg Nesterov , "Eric W. Biederman" , Kees Cook , Sargun Dhillon , Aleksa Sarai , linux-kselftest@vger.kernel.org, Josh Triplett , Jens Axboe , linux-api@vger.kernel.org, Christian Brauner Subject: [PATCH 1/4] pidfd: support PIDFD_NONBLOCK in pidfd_open() Date: Mon, 31 Aug 2020 15:45:48 +0200 Message-Id: <20200831134551.1599689-2-christian.brauner@ubuntu.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200831134551.1599689-1-christian.brauner@ubuntu.com> References: <20200831134551.1599689-1-christian.brauner@ubuntu.com> MIME-Version: 1.0 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Introduce PIDFD_NONBLOCK to support non-blocking pidfd file descriptors. Ever since the introduction of pidfds and more advanced async io various programming languages such as Rust have grown support for async event libraries. These libraries are created to help build epoll-based event loops around file descriptors. A common pattern is to automatically make all file descriptors they manage to O_NONBLOCK. For such libraries the EAGAIN error code is treated specially. When a function is called that returns EAGAIN the function isn't called again until the event loop indicates the the file descriptor is ready. Supporting EAGAIN when waiting on pidfds makes such libraries just work with little effort. In the following patch we will extend waitid() internally to support non-blocking pidfds. Link: https://lore.kernel.org/lkml/20200811181236.GA18763@localhost/ Link: https://github.com/joshtriplett/async-pidfd Cc: Kees Cook Cc: Sargun Dhillon Cc: Oleg Nesterov Suggested-by: Josh Triplett Signed-off-by: Christian Brauner --- include/uapi/linux/pidfd.h | 12 ++++++++++++ kernel/pid.c | 12 +++++++----- 2 files changed, 19 insertions(+), 5 deletions(-) create mode 100644 include/uapi/linux/pidfd.h diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h new file mode 100644 index 000000000000..5406fbc13074 --- /dev/null +++ b/include/uapi/linux/pidfd.h @@ -0,0 +1,12 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ + +#ifndef _UAPI_LINUX_PIDFD_H +#define _UAPI_LINUX_PIDFD_H + +#include +#include + +/* Flags for pidfd_open(). */ +#define PIDFD_NONBLOCK O_NONBLOCK + +#endif /* _UAPI_LINUX_PIDFD_H */ diff --git a/kernel/pid.c b/kernel/pid.c index b2562a7ce525..74ddbff1a6ba 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -43,6 +43,7 @@ #include #include #include +#include struct pid init_struct_pid = { .count = REFCOUNT_INIT(1), @@ -522,7 +523,8 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns) /** * pidfd_create() - Create a new pid file descriptor. * - * @pid: struct pid that the pidfd will reference + * @pid: struct pid that the pidfd will reference + * @flags: flags to pass * * This creates a new pid file descriptor with the O_CLOEXEC flag set. * @@ -532,12 +534,12 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns) * Return: On success, a cloexec pidfd is returned. * On error, a negative errno number will be returned. */ -static int pidfd_create(struct pid *pid) +static int pidfd_create(struct pid *pid, unsigned int flags) { int fd; fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid), - O_RDWR | O_CLOEXEC); + flags | O_RDWR | O_CLOEXEC); if (fd < 0) put_pid(pid); @@ -565,7 +567,7 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags) int fd; struct pid *p; - if (flags) + if (flags & ~PIDFD_NONBLOCK) return -EINVAL; if (pid <= 0) @@ -576,7 +578,7 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags) return -ESRCH; if (pid_has_task(p, PIDTYPE_TGID)) - fd = pidfd_create(p); + fd = pidfd_create(p, flags); else fd = -EINVAL;