On Tue, 10 Jul 2007 20:19:16 -0400 Mingming Cao <cmm@xxxxxxxxxx> wrote: > On Tue, 2007-07-10 at 18:22 -0700, Andrew Morton wrote: > > On Tue, 10 Jul 2007 18:09:40 -0400 Mingming Cao <cmm@xxxxxxxxxx> wrote: > > > > > On Tue, 2007-07-10 at 16:30 -0700, Andrew Morton wrote: > > > > On Sun, 01 Jul 2007 03:37:04 -0400 > > > > Mingming Cao <cmm@xxxxxxxxxx> 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() That assumes an mtime update for every write(). OK, so two writes in a single nanosecond won't be happening. But in that case why is this code: static inline struct timespec ext4_current_time(struct inode *inode) { return (inode->i_sb->s_time_gran < NSEC_PER_SEC) ? current_fs_time(inode->i_sb) : CURRENT_TIME_SEC; } checking (s_time_gran < NSEC_PER_SEC) ?? Overall it is a bit unpleasing to rely upon mtime updates for a correct NFS server implementation: if we were to later decrease s_time_gran (as we might do, for performance reasons), the NFS server implementation starts reporting incorrect information. > > 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? That would work. - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html