On Thu 01-04-21 17:18:05, Amir Goldstein wrote: > > > > > Also I'm somewhat uneasy that it is random (from > > > > > userspace POV) when path event is generated and when not (at least that's > > > > > my impression from the patch - maybe I'm wrong). How difficult would it be > > > > > to get rid of it? I mean what if we just moved say fsnotify_create() call > > > > > wholly up the stack? It would mean more explicit calls to fsnotify_create() > > > > > from filesystems - as far as I'm looking nfsd, overlayfs, cachefiles, > > > > > ecryptfs. But that would seem to be manageable. Also, to maintain sanity, > > > > > > > > 1. I don't think we can do that for all the fsnotify_create() hooks, such as > > > > debugfs for example > > > > 2. It is useless to pass the mount from overlayfs to fsnotify, its a private > > > > mount that users cannot set a mark on anyway and Christian has > > > > promised to propose the same change for cachefiles and ecryptfs, > > > > so I think it's not worth the churn in those call sites > > > > 3. I am uneasy with removing the fsnotify hooks from vfs helpers and > > > > trusting that new callers of vfs_create() will remember to add the high > > > > level hooks, so I prefer the existing behavior remains for such callers > > > > > > > > > > So I read your proposal the wrong way. > > > You meant move fsnotify_create() up *without* passing mount context > > > from overlayfs and friends. > > > > Well, I was thinking that we could find appropriate mount context for > > overlayfs or ecryptfs (which just shows how little I know about these > > filesystems ;) I didn't think of e.g. debugfs. Anyway, if we can make > > mountpoint marks work for directory events at least for most filesystems, I > > think that is OK as well. However it would be then needed to detect whether > > a given filesystem actually supports mount marks for dir events and if not, > > report error from fanotify_mark() instead of silently not generating > > events. > > > > It's not about "filesystems that support mount marks". > mount marks will work perfectly well on overlayfs. > > The thing is if you place a mount mark on the underlying store of > overlayfs (say xfs) and then files are created/deleted by the > overlayfs driver (in xfs) you wont get any events, because > overlayfs uses a private mount clone to perform underlying operations. OK, understood. > So while we CAN get the overlayfs underlying layer mount context > it is irrelevant because no user can setup a mount mark on that > private mount, so no need to bother calling the path hooks. > > This is not the case with nfsd IMO. > With nfsd, when "exporting" a path to clients, nfsd is really exporting > a specific mount (and keeping that mount busy too). > It can even export whole mount topologies. > > But then again, getting the mount context in every nfsd operation > is easy, there is an export context to client requests and the export > context has the exported path. > > Therefore, nfsd is my only user using the vfs helpers that is expected > to call the fsnotify path hooks (other than syscalls). I agree. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
