fscache: Implement cookie invalidation

Add a function to invalidate the cache behind a cookie:

	void fscache_invalidate(struct fscache_cookie *cookie,
				const void *aux_data,
				loff_t size,
				unsigned int flags)

This causes any cached data for the specified cookie to be discarded.  If
the cookie is marked as being in use, a new cache object will be created if
possible and future I/O will use that instead.  In-flight I/O should be
abandoned (writes) or reconsidered (reads).  Each time it is called
cookie->inval_counter is incremented and this can be used to detect
invalidation at the end of an I/O operation.

The coherency data attached to the cookie can be updated and the cookie
size should be reset.  One flag is available, FSCACHE_INVAL_DIO_WRITE,
which should be used to indicate invalidation due to a DIO write on a
file.  This will temporarily disable caching for this cookie.

Changes
=======
ver #2:
 - Should only change to inval state if can get access to cache.

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/163819602231.215744.11206598147269491575.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906909707.143852.18056070560477964891.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967107447.1823006.5945029409592119962.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021512640.640689.11418616313147754172.stgit@warthog.procyon.org.uk/ # v4

1 files changed, 31 insertions, 0 deletions

diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index e6c321e5bf73..0f36d1fac237 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -39,6 +39,8 @@ struct fscache_cookie;
 #define FSCACHE_ADV_WRITE_CACHE		0x00 /* Do cache if written to locally */
 #define FSCACHE_ADV_WRITE_NOCACHE	0x02 /* Don't cache if written to locally */
 
+#define FSCACHE_INVAL_DIO_WRITE		0x01 /* Invalidate due to DIO write */
+
 /*
  * Data object state.
  */
@@ -47,6 +49,7 @@ enum fscache_cookie_state {
 	FSCACHE_COOKIE_STATE_LOOKING_UP,	/* The cache object is being looked up */
 	FSCACHE_COOKIE_STATE_CREATING,		/* The cache object is being created */
 	FSCACHE_COOKIE_STATE_ACTIVE,		/* The cache is active, readable and writable */
+	FSCACHE_COOKIE_STATE_INVALIDATING,	/* The cache is being invalidated */
 	FSCACHE_COOKIE_STATE_FAILED,		/* The cache failed, withdraw to clear */
 	FSCACHE_COOKIE_STATE_LRU_DISCARDING,	/* The cookie is being discarded by the LRU */
 	FSCACHE_COOKIE_STATE_WITHDRAWING,	/* The cookie is being withdrawn */
@@ -153,6 +156,7 @@ extern struct fscache_cookie *__fscache_acquire_cookie(
 extern void __fscache_use_cookie(struct fscache_cookie *, bool);
 extern void __fscache_unuse_cookie(struct fscache_cookie *, const void *, const loff_t *);
 extern void __fscache_relinquish_cookie(struct fscache_cookie *, bool);
+extern void __fscache_invalidate(struct fscache_cookie *, const void *, loff_t, unsigned int);
 
 /**
  * fscache_acquire_volume - Register a volume as desiring caching services
@@ -327,4 +331,31 @@ void __fscache_update_cookie(struct fscache_cookie *cookie, const void *aux_data
 	set_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &cookie->flags);
 }
 
+/**
+ * fscache_invalidate - Notify cache that an object needs invalidation
+ * @cookie: The cookie representing the cache object
+ * @aux_data: The updated auxiliary data for the cookie (may be NULL)
+ * @size: The revised size of the object.
+ * @flags: Invalidation flags (FSCACHE_INVAL_*)
+ *
+ * Notify the cache that an object is needs to be invalidated and that it
+ * should abort any retrievals or stores it is doing on the cache.  This
+ * increments inval_counter on the cookie which can be used by the caller to
+ * reconsider I/O requests as they complete.
+ *
+ * If @flags has FSCACHE_INVAL_DIO_WRITE set, this indicates that this is due
+ * to a direct I/O write and will cause caching to be disabled on this cookie
+ * until it is completely unused.
+ *
+ * See Documentation/filesystems/caching/netfs-api.rst for a complete
+ * description.
+ */
+static inline
+void fscache_invalidate(struct fscache_cookie *cookie,
+			const void *aux_data, loff_t size, unsigned int flags)
+{
+	if (fscache_cookie_enabled(cookie))
+		__fscache_invalidate(cookie, aux_data, size, flags);
+}
+
 #endif /* _LINUX_FSCACHE_H */