Re: dcache: abstract take_name_snapshot() interface

[Al Viro <viro@zeniv.linux.org.uk>]

On Tue, Jan 14, 2020 at 08:06:56PM +0200, Amir Goldstein wrote:
> > // NOTE: release_dentry_name_snapshot() will be needed for both copies.
> > clone_name_snapshot(struct name_snapshot *to, const struct name_snapshot *from)
> > {
> >         to->name = from->name;
> >         if (likely(to->name.name == from->inline_name)) {
> >                 memcpy(to->inline_name, from->inline_name,
> >                         to->name.len);
> >                 to->name.name = to->inline_name;
> >         } else {
> >                 struct external_name *p;
> >                 p = container_of(to->name.name, struct external_name, name[0]);
> >                 atomic_inc(&p->u.count);
> >         }
> > }
> >
> > and be done with that.  Avoids any extensions or tree-wide renamings, etc.
> 
> I started with something like this but than in one of the early
> revisions I needed
> to pass some abstract reference around before cloning the name into the event,
> but with my current patches I can get away with a simple:
> 
> if (data_type == FANOTIFY_EVENT_NAME)
>     clone_name_snapshot(&event->name, data);
> else if (dentry)
>     take_dentry_name_snapshot(&event->name, dentry);
> 
> So that simple interface should be good enough for my needs.

I really think it would be safer that way; do you want me to throw that into
vfs.git (#work.dcache, perhaps)?  I don't have anything going on in the
vicinity, so it's not likely to cause conflicts either way and nothing I'd
seen posted on fsdevel seems to be likely to step into it, IIRC, so...
Up to you.