From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from zeniv.linux.org.uk ([195.92.253.2]:38508 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726412AbeJRHbN (ORCPT ); Thu, 18 Oct 2018 03:31:13 -0400 Date: Thu, 18 Oct 2018 00:33:05 +0100 From: Al Viro To: David Laight Cc: 'Phillip Potter' , "dushistov@mail.ru" , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH] fs: ufs: Remove switch statement from ufs_set_de_type function Message-ID: <20181017233305.GC32577@ZenIV.linux.org.uk> References: <20181017100809.GA9070@pathfinder> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Oct 17, 2018 at 10:11:47AM +0000, David Laight wrote: > From: Phillip Potter > > Sent: 17 October 2018 11:08 > > > > Remove switch statement from ufs_set_de_type function in fs/ufs/util.h > > header and replace with simple assignment. For each case, S_IFx >> 12 > > is equal to DT_x, so in valid cases (mode & S_IFMT) >> 12 should give > > us the correct file type. For invalid cases, upper layer validation > > catches this anyway, so this improves readability and arguably > > performance by assigning (mode & S_IFMT) >> 12 directly. > > > ... > > - case S_IFIFO: > > - de->d_u.d_44.d_type = DT_FIFO; > > - break; > > - default: > > - de->d_u.d_44.d_type = DT_UNKNOWN; > > - } > > + de->d_u.d_44.d_type = (mode & S_IFMT) >> S_SHIFT; > > This requires that the two sets of constants are correctly aligned. They are. BSD folks had (sanely, IMO) put the 'type' bits of st_mode into directory entry verbatim. Again, "symbolic constant" != "can be expected to change"... If, e.g., some port decides to change S_IFIFO, they'll have no end of fun accessing ext*, xfs, ufs, etc. since that value is stored in the on-disk inode and in effect pinned down by that. All S_... constants are universal and going to remain unchanged on any Unices.