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FS-Cache: Provide proper invalidation

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Provide a proper invalidation method rather than relying on the netfs retiring
the cookie it has and getting a new one.  The problem with this is that isn't
easy for the netfs to make sure that it has completed/cancelled all its
outstanding storage and retrieval operations on the cookie it is retiring.

Instead, have the cache provide an invalidation method that will cancel or wait
for all currently outstanding operations before invalidating the cache, and
will cause new operations to queue up behind that.  Whilst invalidation is in
progress, some requests will be rejected until the cache can stack a barrier on
the operation queue to cause new operations to be deferred behind it.

Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
David Howells
2012-12-20 21:52:36 +00:00
parent 9f10523f89
commit ef778e7ae6
11 changed files with 345 additions and 18 deletions
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46
Documentation/filesystems/caching/netfs-api.txt
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@@ -35,8 +35,9 @@ This document contains the following sections:
(12) Index and data file update
(13) Miscellaneous cookie operations
(14) Cookie unregistration
(15) Index and data file invalidation
(16) FS-Cache specific page flags.
(15) Index invalidation
(16) Data file invalidation
(17) FS-Cache specific page flags.
=============================
@@ -767,13 +768,42 @@ the cookies for "child" indices, objects and pages have been relinquished
first.
================================
INDEX AND DATA FILE INVALIDATION
================================
==================
INDEX INVALIDATION
==================
There is no direct way to invalidate an index subtree or a data file. To do
this, the caller should relinquish and retire the cookie they have, and then
acquire a new one.
There is no direct way to invalidate an index subtree. To do this, the caller
should relinquish and retire the cookie they have, and then acquire a new one.
======================
DATA FILE INVALIDATION
======================
Sometimes it will be necessary to invalidate an object that contains data.
Typically this will be necessary when the server tells the netfs of a foreign
change - at which point the netfs has to throw away all the state it had for an
inode and reload from the server.
To indicate that a cache object should be invalidated, the following function
can be called:
void fscache_invalidate(struct fscache_cookie *cookie);
This can be called with spinlocks held as it defers the work to a thread pool.
All extant storage, retrieval and attribute change ops at this point are
cancelled and discarded. Some future operations will be rejected until the
cache has had a chance to insert a barrier in the operations queue. After
that, operations will be queued again behind the invalidation operation.
The invalidation operation will perform an attribute change operation and an
auxiliary data update operation as it is very likely these will have changed.
Using the following function, the netfs can wait for the invalidation operation
to have reached a point at which it can start submitting ordinary operations
once again:
void fscache_wait_on_invalidate(struct fscache_cookie *cookie);
===========================