[PATCH 04/11] VFS: introduce dentry_lookup_continue()

[NeilBrown]

On Wed, 13 Aug 2025, Al Viro wrote:
> On Tue, Aug 12, 2025 at 12:25:07PM +1000, NeilBrown wrote:
> > A few callers operate on a dentry which they already have - unlike the
> > normal case where a lookup proceeds an operation.
> > 
> > For these callers dentry_lookup_continue() is provided where other
> > callers would use dentry_lookup().  The call will fail if, after the
> > lock was gained, the child is no longer a child of the given parent.
> > 
> > There are a couple of callers that want to lock a dentry in whatever
> > its current parent is.  For these a NULL parent can be passed, in which
> > case ->d_parent is used.  In this case the call cannot fail.
> > 
> > The idea behind the name is that the actual lookup occurred some time
> > ago, and now we are continuing with an operation on the dentry.
> > 
> > When the operation completes done_dentry_lookup() must be called.  An
> > extra reference is taken when the dentry_lookup_continue() call succeeds
> > and will be dropped by done_dentry_lookup().
> > 
> > This will be used in smb/server, ecryptfs, and overlayfs, each of which
> > have their own lock_parent() or parent_lock() or similar; and a few
> > other places which lock the parent but don't check if the parent is
> > still correct (often because rename isn't supported so parent cannot be
> > incorrect).
> 
> I would really like the see the conversion of these callers.  You are
> asking for a buy-in for a primitive with specific semantics; that's
> hard to review without seeing how it will be used.
> 

All, or just some?
I use dentry_lookup_continue() in:
  cachefiles: 4 times
  ecryptfs: once
  overlayfs: twice
  smb/server: once
  apparmor: once

Maybe I could include all in the one patch...

NeilBrown