On Thu, 18 Aug 2022, Dave Chinner wrote: > > > Maybe we should just go back to using ctime. ctime is *exactly* what > > NFSv4 wants, as long as its granularity is sufficient to catch every > > single change. Presumably XFS doesn't try to ensure this. How hard > > would it be to get any ctime update to add at least one nanosecond? > > This would be enabled by a mount option, or possibly be a direct request > > from nfsd. > > We can't rely on ctime to be changed during a modification because > O_NOCMTIME exists to enable "user invisible" modifications to be > made. On XFS these still bump iversion, so while they are invisible > to the user, they are still tracked by the filesystem and anything > that wants to know if the inode data/metadata changed. > O_NOCMTIME isn't mentioned in the man page, so it doesn't exist :-( If they are "user invisible", should they then also be "NFS invisible"? I think so. As I understand it, the purpose of O_NOCMTIME is to allow optimisations - do a lot of writes, then update the mtime, thus reducing latency. I think it is perfectly reasonable for all of that to be invisible to NFS. NeilBrown
