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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 3F259C04AAF for ; Tue, 21 May 2019 12:09:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F3A3217D4 for ; Tue, 21 May 2019 12:09:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727999AbfEUMJu convert rfc822-to-8bit (ORCPT ); Tue, 21 May 2019 08:09:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53008 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726344AbfEUMJt (ORCPT ); Tue, 21 May 2019 08:09:49 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CAE443179162; Tue, 21 May 2019 12:09:38 +0000 (UTC) Received: from oldenburg2.str.redhat.com (dhcp-192-219.str.redhat.com [10.33.192.219]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8854750A63; Tue, 21 May 2019 12:09:30 +0000 (UTC) From: Florian Weimer To: Christian Brauner Cc: viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, jannh@google.com, oleg@redhat.com, tglx@linutronix.de, torvalds@linux-foundation.org, arnd@arndb.de, shuah@kernel.org, dhowells@redhat.com, tkjos@android.com, ldv@altlinux.org, miklos@szeredi.hu, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 1/2] open: add close_range() References: <20190521113448.20654-1-christian@brauner.io> Date: Tue, 21 May 2019 14:09:29 +0200 In-Reply-To: <20190521113448.20654-1-christian@brauner.io> (Christian Brauner's message of "Tue, 21 May 2019 13:34:47 +0200") Message-ID: <87tvdoau12.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Tue, 21 May 2019 12:09:49 +0000 (UTC) Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org * Christian Brauner: > +/** > + * __close_range() - Close all file descriptors in a given range. > + * > + * @fd: starting file descriptor to close > + * @max_fd: last file descriptor to close > + * > + * This closes a range of file descriptors. All file descriptors > + * from @fd up to and including @max_fd are closed. > + */ > +int __close_range(struct files_struct *files, unsigned fd, unsigned max_fd) > +{ > + unsigned int cur_max; > + > + if (fd > max_fd) > + return -EINVAL; > + > + rcu_read_lock(); > + cur_max = files_fdtable(files)->max_fds; > + rcu_read_unlock(); > + > + /* cap to last valid index into fdtable */ > + if (max_fd >= cur_max) > + max_fd = cur_max - 1; > + > + while (fd <= max_fd) > + __close_fd(files, fd++); > + > + return 0; > +} This seems rather drastic. How long does this block in kernel mode? Maybe it's okay as long as the maximum possible value for cur_max stays around 4 million or so. Solaris has an fdwalk function: So a different way to implement this would expose a nextfd system call to userspace, so that we can use that to implement both fdwalk and closefrom. But maybe fdwalk is just too obscure, given the existence of /proc. I'll happily implement closefrom on top of close_range in glibc (plus fallback for older kernels based on /proc—with an abort in case that doesn't work because the RLIMIT_NOFILE hack is unreliable unfortunately). Thanks, Florian