On Tue, 2022-08-16 at 16:15 +0100, David Howells wrote: > Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > I think we'll just have to ensure that before we expose this for any > > filesystem that it conforms to some minimum standards. i.e.: it must > > change if there are data or metadata changes to the inode, modulo atime > > changes due to reads on regular files or readdir on dirs. > > > > The local filesystems, ceph and NFS should all be fine. I guess that > > just leaves AFS. If it can't guarantee that, then we might want to avoid > > exposing the counter for it. > > AFS monotonically increments the counter on data changes; doesn't make any > change for metadata changes (other than the file size). > > But you can't assume NFS works as per your suggestion as you don't know what's > backing it (it could be AFS, for example - there's a converter for that). > In that case, the NFS server must synthesize a proper change attr. The NFS spec mandates that it change on most metadata changes. > Further, for ordinary disk filesystems, two data changes may get elided and > only increment the counter once. > Not a problem as long as nothing queried the counter in between the changes. > And then there's mmap... > Not sure how that matters here. > It might be better to reduce the scope of your definition and just say that it > must change if there's a data change and may also be changed if there's a > metadata change. > I'd prefer that we mandate that it change on metadata changes as well. That's what most of the in-kernel users want, and what most of the existing filesystems provide. If AFS can't give that guarantee then we can just omit exposing i_version on it. -- Jeff Layton <jlayton@xxxxxxxxxx>
