From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757623AbbCDAxv (ORCPT ); Tue, 3 Mar 2015 19:53:51 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:58112 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757287AbbCDAxt (ORCPT ); Tue, 3 Mar 2015 19:53:49 -0500 Date: Wed, 4 Mar 2015 00:53:47 +0000 From: Al Viro To: Dan Ehrenberg Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, gwendal@chromium.org, ezequiel@vanguardiasur.com.ar Subject: Re: [RFC PATCH] vfs: Use 12:20 bit major:minor in stat everywhere Message-ID: <20150304005347.GU29656@ZenIV.linux.org.uk> References: <1425429420-13142-1-git-send-email-dehrenberg@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1425429420-13142-1-git-send-email-dehrenberg@chromium.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 03, 2015 at 04:37:00PM -0800, Dan Ehrenberg wrote: > Previously, stat on 32-bit platforms used old-style encoding and > validation of major-minor pairs, with 8:8 bits. However, dev_t is > 32-bits on these platforms, and coreutils seems to be treating the > values as 12:20 new-style values. The only reason to use the old > version is in the implementation of a legacy filesystem format which > only has 16 bits of space. Communicating a 12:20 value to userspace > when sizeof dev_t == 4 can be done on either a 32-bit or 64-bit > platform. > > This patch removes the artificial restriction in major:minor size. > The only backwards incompatibility which results is sometimes stat > succeeds if -EOVERFLOW would be returned otherwise. The legacy > old-style stat call is retained as-is. Umm... You do realize that coreutils are _very_ far from being the only userland programs handling the data returned by stat(2), right? What's to guarantee that your ABI change won't break any of those?