From: David Chinner Subject: Re: [PATCH 4/7][TAKE5] support new modes in fallocate Date: Wed, 27 Jun 2007 09:18:04 +1000 Message-ID: <20070626231803.GQ31489@sgi.com> References: <20070613235217.GS86004887@sgi.com> <20070614091458.GH5181@schatzie.adilger.int> <20070614120413.GD86004887@sgi.com> <20070614193347.GN5181@schatzie.adilger.int> <20070625132810.GA1951@amitarora.in.ibm.com> <20070625134500.GE1951@amitarora.in.ibm.com> <20070625150320.GA8686@amitarora.in.ibm.com> <20070625214626.GJ5181@schatzie.adilger.int> <20070626103247.GA19870@amitarora.in.ibm.com> <20070626153413.GC6652@schatzie.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: "Amit K. Arora" , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, David Chinner , suparna@in.ibm.com, cmm@us.ibm.com, xfs@oss.sgi.com Return-path: Content-Disposition: inline In-Reply-To: <20070626153413.GC6652@schatzie.adilger.int> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue, Jun 26, 2007 at 11:34:13AM -0400, Andreas Dilger wrote: > On Jun 26, 2007 16:02 +0530, Amit K. Arora wrote: > > On Mon, Jun 25, 2007 at 03:46:26PM -0600, Andreas Dilger wrote: > > > Can you clarify - what is the current behaviour when ENOSPC (or some other > > > error) is hit? Does it keep the current fallocate() or does it free it? > > > > Currently it is left on the file system implementation. In ext4, we do > > not undo preallocation if some error (say, ENOSPC) is hit. Hence it may > > end up with partial (pre)allocation. This is inline with dd and > > posix_fallocate, which also do not free the partially allocated space. > > Since I believe the XFS allocation ioctls do it the opposite way (free > preallocated space on error) this should be encoded into the flags. > Having it "filesystem dependent" just means that nobody will be happy. No, XFs does not free preallocated space on error. it is up to the application to clean up. > What I mean is that any data read from the file should have the "appearance" > of being zeroed (whether zeroes are actually written to disk or not). What > I _think_ David is proposing is to allow fallocate() to return without > marking the blocks even "uninitialized" and subsequent reads would return > the old data from the disk. Correct, but for swap files that's not an issue - no user should be able too read them, and FA_MKSWAP would really need root privileges to execute. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group