FS-Cache: Provide a slab for cookie allocation

Provide a slab from which can be allocated the FS-Cache cookies that will be
presented to the netfs.

Also provide a slab constructor and a function to recursively discard a cookie
and its ancestor chain.

Signed-off-by: David Howells <[email protected]>
Acked-by: Steve Dickson <[email protected]>
Acked-by: Trond Myklebust <[email protected]>
Acked-by: Al Viro <[email protected]>
Tested-by: Daire Byrne <[email protected]>
4 files changed