From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:55107 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725905AbfHNIG5 (ORCPT ); Wed, 14 Aug 2019 04:06:57 -0400 Date: Wed, 14 Aug 2019 18:05:47 +1000 From: Dave Chinner Subject: Re: [RFC PATCH v2 01/19] fs/locks: Export F_LAYOUT lease to user space Message-ID: <20190814080547.GJ6129@dread.disaster.area> References: <20190809225833.6657-1-ira.weiny@intel.com> <20190809225833.6657-2-ira.weiny@intel.com> <20190809235231.GC7777@dread.disaster.area> <20190812173626.GB19746@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190812173626.GB19746@iweiny-DESK2.sc.intel.com> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Ira Weiny Cc: Andrew Morton , Jason Gunthorpe , Dan Williams , Matthew Wilcox , Jan Kara , Theodore Ts'o , John Hubbard , Michal Hocko , linux-xfs@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org On Mon, Aug 12, 2019 at 10:36:26AM -0700, Ira Weiny wrote: > On Sat, Aug 10, 2019 at 09:52:31AM +1000, Dave Chinner wrote: > > On Fri, Aug 09, 2019 at 03:58:15PM -0700, ira.weiny@intel.com wrote: > > > + /* > > > + * NOTE on F_LAYOUT lease > > > + * > > > + * LAYOUT lease types are taken on files which the user knows that > > > + * they will be pinning in memory for some indeterminate amount of > > > + * time. > > > > Indeed, layout leases have nothing to do with pinning of memory. > > Yep, Fair enough. I'll rework the comment. > > > That's something an application taht uses layout leases might do, > > but it largely irrelevant to the functionality layout leases > > provide. What needs to be done here is explain what the layout lease > > API actually guarantees w.r.t. the physical file layout, not what > > some application is going to do with a lease. e.g. > > > > The layout lease F_RDLCK guarantees that the holder will be > > notified that the physical file layout is about to be > > changed, and that it needs to release any resources it has > > over the range of this lease, drop the lease and then > > request it again to wait for the kernel to finish whatever > > it is doing on that range. > > > > The layout lease F_RDLCK also allows the holder to modify > > the physical layout of the file. If an operation from the > > lease holder occurs that would modify the layout, that lease > > holder does not get notification that a change will occur, > > but it will block until all other F_RDLCK leases have been > > released by their holders before going ahead. > > > > If there is a F_WRLCK lease held on the file, then a F_RDLCK > > holder will fail any operation that may modify the physical > > layout of the file. F_WRLCK provides exclusive physical > > modification access to the holder, guaranteeing nothing else > > will change the layout of the file while it holds the lease. > > > > The F_WRLCK holder can change the physical layout of the > > file if it so desires, this will block while F_RDLCK holders > > are notified and release their leases before the > > modification will take place. > > > > We need to define the semantics we expose to userspace first..... > > Agreed. I believe I have implemented the semantics you describe above. Do I > have your permission to use your verbiage as part of reworking the comment and > commit message? Of course. :) Cheers, Dave. -- Dave Chinner david@fromorbit.com