Re: fsnotify path hooks

[Jan Kara <jack@suse.cz>]

On Thu 08-04-21 18:11:31, Amir Goldstein wrote:
> > > FYI, I tried your suggested approach above for fsnotify_xattr(),
> > > but I think I prefer to use an explicit flavor fsnotify_xattr_mnt()
> > > and a wrapper fsnotify_xattr().
> > > Pushed WIP to fsnotify_path_hooks branch. It also contains
> > > some unstashed "fix" patches to tidy up the previous hooks.
> >
> > What's in fsnotify_path_hooks branch looks good to me wrt xattr hooks.
> > I somewhat dislike about e.g. the fsnotify_create() approach you took is
> > that there are separate hooks fsnotify_create() and fsnotify_create_path()
> > which expose what is IMO an internal fsnotify detail of what are different
> > event types. I'd say it is more natural (from VFS POV) to have just a
> > single hook and fill in as much information as available... Also from
> 
> So to be clear, you do NOT want additional wrappers like this and
> you prefer to have the NULL mnt argument explicit in all callers?
> 
> static inline void fsnotify_xattr(struct dentry *dentry)
> {
>         fsnotify_xattr_mnt(NULL, dentry);
> }
> 
> For fsnotify_xattr() it does not matter so much, but fsnotify_create/mkdir()
> have quite a few callers in special filesystems.

Yes, I prefer explicit NULL mnt argument to make it obvious we are going to
miss something in this case. I agree it's going to be somewhat bigger churn
but it isn't that bad (10 + 6 callers).

> > outside view, it is unclear that e.g. vfs_create() will generate some types
> > of fsnotify events but not all while e.g. do_mknodat() will generate all
> > fsnotify events. That's why I'm not sure whether a helper like vfs_create()
> > in your tree is the right abstraction since generating one type of fsnotify
> > event while not generating another type should be a very conscious decision
> > of the implementor - basically if you have no other option.
> 
> I lost you here.

Sorry, I was probably too philosophical here ;)

> Are you ok with vfs_create() vs. vfs_create_nonotify()?

I'm OK with vfs_create_nonotify(). I have a problem with vfs_create()
because it generates inode + fs events but does not generate mount events
which is just strange (although I appreciate the technical reason behind
it :).

> How do you propose to change fsnotify hooks in vfs_create()?

So either pass 'mnt' to vfs_create() - as we discussed, this may be
actually acceptable these days due to idmapped mounts work - and generate
all events there, or make vfs_create() not generate any fsnotify events and
create new vfs_create_notify() which will take the 'mnt' and generate
events. Either is fine with me and more consistent than what you currently
propose. Thoughts?

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR