[PATCH 00/22] cache cursors: an introduction

[Chuck Lever <cel@citi.umich.edu>]

[ This series is posted for review and comments. ]

The following patch series introduces an abstraction called a "cache
cursor" that will eventually allow us to replace the current
active_cache array with something else.

A cache cursor represents a position inside the cache.  This position
has a cache_entry associated with it, of course, but since the cache
is ordered, a cache cursor also has the concept of next, previous,
and end-of-cache.

With a cache cursor we can build a simple iterator mechanism that
calls a particular function for every entry in the cache, in order.
This allows us to hide further the specifics of the active cache
implementation -- the function gets to see the cache cursor and
an element, but does not have direct access to the cache and cannot
assume it has a particular structure.

Currently the cache cursor type is just a structure with an integer
in it, so it largely mimics the existing implementation.

This patch series is against the "proposed updates" branch, as of
a couple of days ago.  It has been tested via "make test" and I'm
currently using it for my own work without issue.

Signed-off-by: Chuck Lever <cel@netapp.com>
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