On Thu, 28 Apr 2022 at 06:46, NeilBrown <neilb@xxxxxxx> wrote: > > On Tue, 26 Apr 2022, Daire Byrne wrote: > > On Tue, 26 Apr 2022 at 02:36, NeilBrown <neilb@xxxxxxx> wrote: > > > > > > On Tue, 26 Apr 2022, Daire Byrne wrote: > > > > > > > > I'll stare at fs/nfsd/vfs.c for a bit but I probably lack the > > > > expertise to make it work. > > > > > > Staring at code is good for the soul .... but I'll try to schedule time > > > to work on this patch again - make it work from nfsd and also make it > > > handle rename. > > > > Yea, I stared at it for quite a while this morning and no amount of > > coffee was going to help me figure out how best to proceed. > > yes, it isn't at all straight forward - is it? > We probably need quite a bit of surgery in nfsd/vfs.c to make it more > similar to fs/namei.c. In particularly we will need to use > filename_create() instead of lookup_one_len(). > > There is a potential cost to doing this though. The NFS protocol allows > the server to report the change-id of the directory before and after a > create/unlink operation so that the client can determine if it is the > only one making changes to the directory, and so can keep its cache. > This requires the pre/post to be atomic - which requires an exclusive > lock. > If we change nfsd to use a shared lock on the directory, then it cannot > report atomic pre/post attributes, so the client will have to flush its > cache more often. > > Support parallel creates and atomic attributes we would need to enhance > the filesystem interface so the fs can report the attributes for each > create. Could get messy. > > This doesn't actually matter for NFS re-export because it doesn't > support atomic attributes anyway. It also doesn't matter if multiple > clients are changing tghe one directory. But I think we do want to keep atomic > attributes for exporting other filesystems in other use-cases. > > It's starting to get messy. Not impossible, just messy. Messy takes > longer :-) Thanks for looking Neil. I don't feel quite so dumb admitting that it was way above my level! :) Like I said, this isn't a blocker for us but definitely a nice to have feature. Slow progress is still good progress. Cheers, Daire
