Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754764AbcDMTFu (ORCPT ); Wed, 13 Apr 2016 15:05:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35867 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751463AbcDMTFs (ORCPT ); Wed, 13 Apr 2016 15:05:48 -0400 From: "Richard W.M. Jones" To: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, akpm@linux-foundation.org, luto@kernel.org, viro@zeniv.linux.org.uk, mathieu.desnoyers@efficios.com, zab@redhat.com, emunson@akamai.com, paulmck@linux.vnet.ibm.com, aarcange@redhat.com, josh@joshtriplett.org, xemul@parallels.com, sfr@canb.auug.org.au, milosz@adfin.com, rostedt@goodmis.org, arnd@arndb.de, ebiederm@xmission.com, gorcunov@openvz.org, iulia.manda21@gmail.com, dave.hansen@linux.intel.com, mguzik@redhat.com, adobriyan@gmail.com, dave@stgolabs.net, linux-api@vger.kernel.org, gorcunov@gmail.com, fw@deneb.enyo.de, walters@verbum.org Subject: [PATCH v4 0/3] vfs: Define new syscall umask2 [formerly getumask] Date: Wed, 13 Apr 2016 20:05:33 +0100 Message-Id: <1460574336-18930-1-git-send-email-rjones@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1231 Lines: 37 v3 -> v4: - Rename the syscall: getumask becomes umask2. - Add flags parameter, with one flag (UMASK_GET_MASK). - Expand the rationale for this change in the first commit message. - Add a selftest. - Retest everything. -------------------- It's not possible to read the process umask without also modifying it, which is what umask(2) does. A library cannot read umask safely, especially if the main program might be multithreaded. This patch series adds a new system call "umask2". This adds a flags parameter. Specifying flags=UMASK_GET_MASK allows the umask of the current process to be read without modifying it. This leaves open the possibility in future of adding a per-thread umask, set or read with other flags. This is not implemented. Another approach to this has been attempted before, adding something to /proc, although it didn't go anywhere. See: http://comments.gmane.org/gmane.linux.kernel/1292109 Another way to solve this would be to add a thread-safe getumask to glibc. Since glibc could own the mutex, this would permit libraries linked to this glibc to read umask safely. I should also note that man-pages documents getumask(3), but no version of glibc has ever implemented it. Rich.