From: Mingming Cao Subject: Re: [EXT4 set 4][PATCH 1/5] i_version:64 bit inode version Date: Tue, 10 Jul 2007 20:19:16 -0400 Message-ID: <1184113156.20193.13.camel@localhost.localdomain> References: <1183275424.4010.126.camel@localhost.localdomain> <20070710163038.ceb2ae94.akpm@linux-foundation.org> <1184105380.3759.65.camel@localhost.localdomain> <20070710182237.e2f88bf3.akpm@linux-foundation.org> Reply-To: cmm@us.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, nfsv4@linux-nfs.org, linux-kernel@vger.kernel.org To: Andrew Morton Return-path: In-Reply-To: <20070710182237.e2f88bf3.akpm@linux-foundation.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: nfsv4-bounces@linux-nfs.org Errors-To: nfsv4-bounces@linux-nfs.org List-Id: linux-ext4.vger.kernel.org On Tue, 2007-07-10 at 18:22 -0700, Andrew Morton wrote: > On Tue, 10 Jul 2007 18:09:40 -0400 Mingming Cao wrote: > > > On Tue, 2007-07-10 at 16:30 -0700, Andrew Morton wrote: > > > On Sun, 01 Jul 2007 03:37:04 -0400 > > > Mingming Cao wrote: > > > > > > > This patch converts the 32-bit i_version in the generic inode to a 64-bit > > > > i_version field. > > > > > > > > > > That's obvious from the patch. But what was the reason for making this > > > (unrelated to ext4) change? > > > > > > > The need is came from NFSv4 > > > > On Fri, 2007-05-25 at 18:25 +0200, Jean noel Cordenner wrote: > > > Hi, > > > > > > This is an update of the i_version patch. > > > The i_version field is a 64bit counter that is set on every inode > > > creation and that is incremented every time the inode data is modified > > > (similarly to the "ctime" time-stamp). > > > The aim is to fulfill a NFSv4 requirement for rfc3530: > > > "5.5. Mandatory Attributes - Definitions > > > Name # DataType Access Description > > > ___________________________________________________________________ > > > change 3 uint64 READ A value created by the > > > server that the client can use to determine if file > > > data, directory contents or attributes of the object > > > have been modified. The servermay return the object's > > > time_metadata attribute for this attribute's value but > > > only if the filesystem object can not be updated more > > > frequently than the resolution of time_metadata. > > > " > > > > > > > > Please update the changelog for this. > > > > > > > Is above description clear to you? > > > > Yes, thanks. It doesn't actually tell us why we want to implement > this attribute and it doesn't tell us what the implications of failing > to do so are, but I guess we can take that on trust from the NFS guys. > > But I suspect the ext4 implementation doesn't actually do this. afaict we > won't update i_version for file overwrites (especially if s_time_gran can > indeed be 1,000,000,000) and of course for MAP_SHARED modifications. What > would be the implications of this? > In the case of overwrite (file date updated), I assume the ctime/mtime is being updated and the inode is being dirtied, so the version number is being updated. vfs_write()->.. ->__generic_file_aio_write_nolock() ->file_update_time() ->mark_inode_dirty_sync() ->__mark_inode_dirty(I_DIRTY_SYNC) ->ext4_dirty_inode() ->ext4_mark_inode_dirty() > And how does the NFS server know that the filesystem implements i_version? > Will a zero-value of i_version have special significance, telling the > server to not send this attribute, perhaps? Bruce raised up this question a few days back when he reviewed this patch, I think the solution is add a superblock flag for fs support inode versioning, probably at VFS layer? Mingming