filesystems/nfs/rpc-cache.rst

21   - mapping from IP address to client name
22   - mapping from client name and filesystem to export options
23   - mapping from UID to list of GIDs, to work around NFS's limitation
25   - mappings between local UID/GID and remote UID/GID for sites that
27   - mapping from network identify to public key for crypto authentication.
31    - general cache lookup with correct locking
32    - supporting 'NEGATIVE' as well as positive entries
33    - allowing an EXPIRED time on cache items, and removing
34      items after they expire, and are no longer in-use.
35    - making requests to user-space to fill in cache entries
36    - allowing user-space to directly set entries in the cache
37    - delaying RPC requests that depend on as-yet incomplete
38      cache entries, and replaying those requests when the cache entry
40    - clean out old entries as they expire.
43 ----------------
45 -  A cache needs a datum to store.  This is in the form of a
51 -  A cache needs a "cache_detail" structure that
89       Format a request to be send to user-space for an item
98       cache entry.  It is in 'buf' of length 'len'.
104 -  A cache needs to be registered using cache_register().  This
109 -------------
113 This will be passed to ->match to identify the target entry.  If no
114 entry is found, a new entry will be create, added to the cache, and
118 if the data is valid, and may initiate an up-call to get fresh data.
119 cache_check will return -ENOENT in the entry is negative or if an up
120 call is needed but not possible, -EAGAIN if an upcall is pending,
129 revisited (->revisit).  It is expected that this method will
141 ------------------
156   - a key
157   - an expiry time
158   - a content.
165 lookup fails, or when it succeeds but finds an entry that may soon
167 user-space.  These requests appear in the channel file.
174 Thus a user-space helper is likely to::
186 Each cache should define a "cache_parse" method which takes a message
187 written from user-space and processes it.  It should return an error
190 Each cache should also define a "cache_request" method which
198   entry will fail.  This is partly for backward compatibility: The
203 -----------------------
214 -  If a field begins '\x' then it must contain an even number of
217 -  otherwise a \ in the field must be followed by 3 octal digits