Re: [bug report] NFS: Support statx_get and statx_set ioctls

[Trond Myklebust <trondmy@hammerspace.com>]

On Wed, 2022-01-12 at 22:30 -0800, Jeremy Allison wrote:
> On Thu, Jan 13, 2022 at 05:52:40AM +0200, Amir Goldstein wrote:
> > 
> > To add one more terminology to the mix - when Samba needed to cope
> > with these two terminologies they came up with itime for
> > "instantiation time"
> > (one may also consider it "immutable time").
> 
> No, that's not what itime is. It's used as the basis
> for the fileid return as MacOSX clients insist on no-reuse
> of inode numbers when a file is deleted then re-created,
> and ext4 will re-use the same inode.

So basically it serves more or less the same purpose as the generation
counter that most Linux filesystems use in the filehandle to provide
similar only-once semantics?

> 
> Samba uses btime for "birth time", and will use statx
> to get it from the filesystem but then store it in
> the dos.attribute EA so it can be modified if the
> client sets it.

Right. That appears to be a difference between Windows and Linux. In
most Linux filesystems, the btime is set by the filesystem at file
creation time, however Windows allows it to be set by the application,
presumably for the purpose of backup/restore?

NFSv4 supports both modes for the btime.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com