On Mon 27-05-24 09:29:48, hch@xxxxxxxxxxxxx wrote: > On Mon, May 27, 2024 at 03:38:40PM +0000, Trond Myklebust wrote: > > If your use case isn't NFS servers, then what use case are you > > targeting, and how do you expect those applications to use this API? > > The main user of the open by handle syscalls seems to be fanotify > magic. So some fanotify users may use open_by_handle_at() and name_to_handle_at() but we specifically designed fanotify to not depend on this mount id feature of the API (because it wasn't really usable couple of years ago when we were designing this with Amir). fanotify returns fsid + fhandle in its events and userspace is expected to build a mapping of fsid -> "whatever it needs to identify a filesystem" when placing fanotify marks. If it wants to open file / directory where events happened, then this usually means keeping fsid -> "some open fd on fs" mapping so that it can then use open_by_handle_at() for opening. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
