From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753509AbaBYXmK (ORCPT ); Tue, 25 Feb 2014 18:42:10 -0500 Received: from mail-pb0-f41.google.com ([209.85.160.41]:48991 "EHLO mail-pb0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753093AbaBYXmI (ORCPT ); Tue, 25 Feb 2014 18:42:08 -0500 Date: Tue, 25 Feb 2014 15:41:20 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Dave Chinner cc: Andrew Morton , "Theodore Ts'o" , Namjae Jeon , viro@zeniv.linux.org.uk, bpm@sgi.com, adilger.kernel@dilger.ca, jack@suse.cz, mtk.manpages@gmail.com, lczerner@redhat.com, linux-fsdevel@vger.kernel.org, xfs@oss.sgi.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Namjae Jeon , Ashish Sangwan Subject: Re: [PATCH v5 1/10] fs: Add new flag(FALLOC_FL_COLLAPSE_RANGE) for fallocate In-Reply-To: <20140223213606.GE4317@dastard> Message-ID: References: <1392741464-20029-1-git-send-email-linkinjeon@gmail.com> <20140222140625.GD26637@thunk.org> <20140223213606.GE4317@dastard> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 24 Feb 2014, Dave Chinner wrote: > On Sat, Feb 22, 2014 at 09:06:25AM -0500, Theodore Ts'o wrote: > > On Wed, Feb 19, 2014 at 01:37:43AM +0900, Namjae Jeon wrote: > > > + /* > > > + * There is no need to overlap collapse range with EOF, in which case > > > + * it is effectively a truncate operation > > > + */ > > > + if ((mode & FALLOC_FL_COLLAPSE_RANGE) && > > > + (offset + len >= i_size_read(inode))) > > > + return -EINVAL; > > > + > > > > I wonder if we should just translate a collapse range that is > > equivalent to a truncate operation to, in fact, be a truncate > > operation? > > Trying to collapse a range that extends beyond EOF, IMO, is likely > to only happen if the DVR/NLE application is buggy. Hence I think > that telling the application it is doing something that is likely to > be wrong is better than silently truncating the file.... I do agree with Ted on this point. This is not an xfs ioctl added for one DVR/NLE application, it's a mode of a Linux system call. We do not usually reject with an error when one system call happens to ask for something which can already be accomplished another way; nor nanny our callers. It seems natural to me that COLLAPSE_RANGE should support beyond EOF; unless that adds significantly to implementation difficulties? Actually, is it even correct to fail at EOF? What if fallocation with FALLOC_FL_KEEP_SIZE was used earlier, to allocate beyond EOF: shouldn't it be possible to shift that allocation down, along with the EOF, rather than leave it behind as a stranded island? Hugh