[PATCH 0/3} Change ->mkdir() and vfs_mkdir() to return a dentry

[NeilBrown]

This is a small set of patches which are needed before we can make the
locking on directory operations more fine grained.  I think they are
useful even if we don't go that direction.

Some callers of vfs_mkdir() need to operation on the resulting directory
but cannot be guaranteed that the dentry will be hashed and positive on
success - another dentry might have been used.

This patch changes ->mkdir to return a dentry, changes NFS in particular
to return the correct dentry (I believe it is the only filesystem to
possibly not use the given dentry), and changes vfs_mkdir() to return
that dentry, removing the look that a few callers currently need.

I have not Cc: the developers of all the individual filesystems - only
NFS.  I have build-tested all the changes except hostfs.  I can email
them explicitly if/when this is otherwise acceptable.  If anyone sees
this on fs-devel and wants to provide a pre-emptive ack I will collect
those and avoid further posting for those fs.

Thanks,
NeilBrown