[PATCH 0/3] cephfs: prepare for changes to VFS locking

[NeilBrown]

I am working on changes to directory locking.  The medium term goal is
to lift d_alloc_parallel() locking above i_rwsem, so d_alloc_paralle()
can be run unlocked, and consequently cannot be called when ->i_rwsem is
held.

The requires:
 1/ that d_alloc_parallel() not be called while i_rwsem is held and also
    that d_alloc()/d_splice_alias() not be used (unless the filesystems
    doesn't support creating objects).
    cephfs uses d_alloc()/d_splice_alias() when priming the dcache from
    the results of readdir.  A new interface d_alloc_trylock()
    is now available and can be used instead.

 2/ a dentry must not be d_drop()ed while an operation is ongoing, as an
    unlocked d_alloc_parallel() would then be able to create a new
    dentry with the same name.  cephfs calls d_drop() in couple of places
    before d_splice_alias() but this is no longer needed as d_splice_alias()
    handles spliced aliases now.

Patch 3/3 isn't strictly needed here but I'd like to deprecate d_add()
in favour of d_splice_alias() as the latter now does everything the
former can do.  So the last patch removes uses of d_add() from fs/ceph.

The patches depend on patches recently added to the vfs tree.  I would
prefer these land in that tree too with an Acked-by or similar from cifs
maintainers.

Thanks,
NeilBrown

 [PATCH 1/3] cephfs: Use d_alloc_trylock() in
 [PATCH 2/3] cephfs: Don't d_drop() before d_splice_alias()
 [PATCH 3/3] cephfs: stop using d_add()