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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 F3818C433FE for ; Thu, 10 Dec 2020 00:27:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CDB6D22D04 for ; Thu, 10 Dec 2020 00:27:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726855AbgLJA1l (ORCPT ); Wed, 9 Dec 2020 19:27:41 -0500 Received: from 4.mo7.mail-out.ovh.net ([178.32.122.254]:55055 "EHLO 4.mo7.mail-out.ovh.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726615AbgLJA1l (ORCPT ); Wed, 9 Dec 2020 19:27:41 -0500 X-Greylist: delayed 8398 seconds by postgrey-1.27 at vger.kernel.org; Wed, 09 Dec 2020 19:27:39 EST Received: from player787.ha.ovh.net (unknown [10.108.54.97]) by mo7.mail-out.ovh.net (Postfix) with ESMTP id D7EA41871BE for ; Wed, 9 Dec 2020 23:00:43 +0100 (CET) Received: from sk2.org (82-65-25-201.subs.proxad.net [82.65.25.201]) (Authenticated sender: steve@sk2.org) by player787.ha.ovh.net (Postfix) with ESMTPSA id C87E51931C761; Wed, 9 Dec 2020 22:00:37 +0000 (UTC) Authentication-Results: garm.ovh; auth=pass (GARM-96R0015a9f0d6f-a3f8-409a-918c-52812c8d5d66, 8622D3A4C020BD08BE34C4B7C738CCED01E4E747) smtp.auth=steve@sk2.org From: Stephen Kitt To: linux-man@vger.kernel.org, Alejandro Colomar , Michael Kerrisk Cc: Christian Brauner , linux-kernel@vger.kernel.org, Stephen Kitt Subject: [PATCH v2] close_range.2: new page documenting close_range(2) Date: Wed, 9 Dec 2020 23:00:23 +0100 Message-Id: <20201209220023.17912-1-steve@sk2.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Ovh-Tracer-Id: 5263300591903526162 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedujedrudejkedgudehjecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfqggfjpdevjffgvefmvefgnecuuegrihhlohhuthemucehtddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpefhvffufffkofgggfestdekredtredttdenucfhrhhomhepufhtvghphhgvnhcumfhithhtuceoshhtvghvvgesshhkvddrohhrgheqnecuggftrfgrthhtvghrnhepteegudfgleekieekteeggeetveefueefteeugfduieeitdfhhedtfeefkedvfeefnecukfhppedtrddtrddtrddtpdekvddrieehrddvhedrvddtudenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhhouggvpehsmhhtphdqohhuthdphhgvlhhopehplhgrhigvrhejkeejrdhhrgdrohhvhhdrnhgvthdpihhnvghtpedtrddtrddtrddtpdhmrghilhhfrhhomhepshhtvghvvgesshhkvddrohhrghdprhgtphhtthhopehlihhnuhigqdhmrghnsehvghgvrhdrkhgvrhhnvghlrdhorhhg Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org This documents close_range(2) based on information in 278a5fbaed89dacd04e9d052f4594ffd0e0585de and 60997c3d45d9a67daf01c56d805ae4fec37e0bd8. Signed-off-by: Stephen Kitt --- V2: unsigned int to match the kernel declarations groff and grammar tweaks CLOSE_RANGE_UNSHARE unshares *and* closes Explain that EMFILE and ENOMEM can occur with C_R_U "Conforming to" phrasing Detailed explanation of CLOSE_RANGE_UNSHARE Reading /proc isn't common man2/close_range.2 | 138 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 138 insertions(+) create mode 100644 man2/close_range.2 diff --git a/man2/close_range.2 b/man2/close_range.2 new file mode 100644 index 000000000..403142b33 --- /dev/null +++ b/man2/close_range.2 @@ -0,0 +1,138 @@ +.\" Copyright (c) 2020 Stephen Kitt +.\" +.\" %%%LICENSE_START(VERBATIM) +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and authors of this work. +.\" %%%LICENSE_END +.\" +.TH CLOSE_RANGE 2 2020-12-08 "Linux" "Linux Programmer's Manual" +.SH NAME +close_range \- close all file descriptors in a given range +.SH SYNOPSIS +.nf +.B #include +.PP +.BI "int close_range(unsigned int " first ", unsigned int " last ", unsigned int " flags ); +.fi +.SH DESCRIPTION +The +.BR close_range () +system call closes all open file descriptors from +.I first +to +.I last +(included). +.PP +Errors closing a given file descriptor are currently ignored. +.PP +.I flags +can be set to +.B CLOSE_RANGE_UNSHARE +to unshare the range of file descriptors from any other processes, +before closing them, avoiding races with other threads sharing the +file descriptor table. +.SH RETURN VALUE +On success, +.BR close_range () +returns 0. +On error, \-1 is returned and +.I errno +is set to indicate the cause of the error. +.SH ERRORS +.TP +.B EINVAL +.I flags +is not valid, or +.I first +is greater than +.IR last . +.PP +The following can occur with +.B CLOSE_RANGE_UNSHARE +(when constructing the new descriptor table): +.TP +.B EMFILE +The per-process limit on the number of open file descriptors has been reached +(see the description of +.B RLIMIT_NOFILE +in +.BR getrlimit (2)). +.TP +.B ENOMEM +Insufficient kernel memory was available. +.SH VERSIONS +.BR close_range () +first appeared in Linux 5.9. +.SH CONFORMING TO +.BR close_range () +is a nonstandard function that is also present on FreeBSD. +.SH NOTES +Currently, there is no glibc wrapper for this system call; call it using +.BR syscall (2). +.PP +.B CLOSE_RANGE_UNSHARE +is conceptually equivalent to +.PP +.in +4n +.EX +unshare(CLONE_FILES); +close_range(first, last, 0); +.EE +.in +.PP +but can be more efficient: if the unshared range extends past the +current maximum number of file descriptors allocated in the caller's +file descriptor table (the common case when +.I last +is +.BR ~0U ), +the kernel will unshare a new file descriptor +table for the caller up to +.IR first . +This avoids subsequent close calls entirely; the whole operation is +complete once the table is unshared. +.SH USE CASES +.\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de +.\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8 +.SS Closing file descriptors before exec +File descriptors can be closed safely using +.PP +.in +4n +.EX +/* we don't want anything past stderr here */ +close_range(3, ~0U, CLOSE_RANGE_UNSHARE); +execve(....); +.EE +.in +.SS Closing all open file descriptors +To avoid blindly closing file descriptors in the range of possible +file descriptors, this is sometimes implemented (on Linux) by listing +open file descriptors in +.I /proc/self/fd/ +and calling +.BR close (2) +on each one. +.BR close_range () +can take care of this without requiring +.I /proc +and with a single system call, which provides significant performance +benefits. +.SH SEE ALSO +.BR close (2) base-commit: b5dae3959625f5ff378e9edf9139057d1c06bb55 -- 2.20.1