fscache: Provide a means to begin an operation

Provide a function to begin a read operation:

	int fscache_begin_read_operation(
		struct netfs_cache_resources *cres,
		struct fscache_cookie *cookie)

This is primarily intended to be called by network filesystems on behalf of
netfslib, but may also be called to use the I/O access functions directly.
It attaches the resources required by the cache to cres struct from the
supplied cookie.

This holds access to the cache behind the cookie for the duration of the
operation and forces cache withdrawal and cookie invalidation to perform
synchronisation on the operation.  cres->inval_counter is set from the
cookie at this point so that it can be compared at the end of the
operation.

Note that this does not guarantee that the cache state is fully set up and
able to perform I/O immediately; looking up and creation may be left in
progress in the background.  The operations intended to be called by the
network filesystem, such as reading and writing, are expected to wait for
the cookie to move to the correct state.

This will, however, potentially sleep, waiting for a certain minimum state
to be set or for operations such as invalidate to advance far enough that
I/O can resume.


Also provide a function for the cache to call to wait for the cache object
to get to a state where it can be used for certain things:

	bool fscache_wait_for_operation(struct netfs_cache_resources *cres,
					enum fscache_want_stage stage);

This looks at the cache resources provided by the begin function and waits
for them to get to an appropriate stage.  There's a choice of wanting just
some parameters (FSCACHE_WANT_PARAM) or the ability to do I/O
(FSCACHE_WANT_READ or FSCACHE_WANT_WRITE).

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819603692.215744.146724961588817028.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906910672.143852.13856103384424986357.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967110245.1823006.2239170567540431836.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021513617.640689.16627329360866150606.stgit@warthog.procyon.org.uk/ # v4

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 1ad56bfd9d72..566497cf5f13 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -67,6 +67,10 @@ struct fscache_cache_ops {
 	/* Invalidate an object */
 	bool (*invalidate_cookie)(struct fscache_cookie *cookie);
 
+	/* Begin an operation for the netfs lib */
+	bool (*begin_operation)(struct netfs_cache_resources *cres,
+				enum fscache_want_state want_state);
+
 	/* Prepare to write to a live cache object */
 	void (*prepare_to_write)(struct fscache_cookie *cookie);
 };
@@ -101,6 +105,8 @@ extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
 extern void fscache_cookie_lookup_negative(struct fscache_cookie *cookie);
 extern void fscache_resume_after_invalidation(struct fscache_cookie *cookie);
 extern void fscache_caching_failed(struct fscache_cookie *cookie);
+extern bool fscache_wait_for_operation(struct netfs_cache_resources *cred,
+				       enum fscache_want_state state);
 
 /**
  * fscache_cookie_state - Read the state of a cookie
@@ -129,4 +135,9 @@ static inline void *fscache_get_key(struct fscache_cookie *cookie)
 		return cookie->key;
 }
 
+static inline struct fscache_cookie *fscache_cres_cookie(struct netfs_cache_resources *cres)
+{
+	return cres->cache_priv;
+}
+
 #endif /* _LINUX_FSCACHE_CACHE_H */