fscache: Add a function to begin an cache op from a netfslib request

Add a function to begin an cache read or write operation from a netfslib
I/O request.  This function can then be pointed to directly by the network
filesystem's netfs_request_ops::begin_cache_operation op pointer.

Ideally, netfslib would just call into fscache directly, but that would
cause dependency cycles as fscache calls into netfslib directly.

Signed-off-by: David Howells <dhowells@redhat.com>

fs/9p/vfs_addr.c

@@ -89,25 +89,10 @@ static void v9fs_free_request(struct netfs_io_request *rreq)
 	p9_client_clunk(fid);
 }
 
-/**
- * v9fs_begin_cache_operation - Begin a cache operation for a read
- * @rreq: The read request
- */
-static int v9fs_begin_cache_operation(struct netfs_io_request *rreq)
-{
-#ifdef CONFIG_9P_FSCACHE
-	struct fscache_cookie *cookie = v9fs_inode_cookie(V9FS_I(rreq->inode));
-
-	return fscache_begin_read_operation(&rreq->cache_resources, cookie);
-#else
-	return -ENOBUFS;
-#endif
-}
-
 const struct netfs_request_ops v9fs_req_ops = {
 	.init_request		= v9fs_init_request,
 	.free_request		= v9fs_free_request,
-	.begin_cache_operation	= v9fs_begin_cache_operation,
+	.begin_cache_operation	= fscache_begin_cache_operation,
 	.clamp_length		= v9fs_clamp_length,
 	.issue_read		= v9fs_issue_read,
 };

fs/afs/file.c

@@ -358,18 +358,6 @@ static int afs_init_request(struct netfs_io_request *rreq, struct file *file)
 	return 0;
 }
 
-static int afs_begin_cache_operation(struct netfs_io_request *rreq)
-{
-#ifdef CONFIG_AFS_FSCACHE
-	struct afs_vnode *vnode = AFS_FS_I(rreq->inode);
-
-	return fscache_begin_read_operation(&rreq->cache_resources,
-					    afs_vnode_cache(vnode));
-#else
-	return -ENOBUFS;
-#endif
-}
-
 static int afs_check_write_begin(struct file *file, loff_t pos, unsigned len,
 				 struct folio *folio, void **_fsdata)
 {
@@ -386,7 +374,7 @@ static void afs_free_request(struct netfs_io_request *rreq)
 const struct netfs_request_ops afs_req_ops = {
 	.init_request		= afs_init_request,
 	.free_request		= afs_free_request,
-	.begin_cache_operation	= afs_begin_cache_operation,
+	.begin_cache_operation	= fscache_begin_cache_operation,
 	.check_write_begin	= afs_check_write_begin,
 	.issue_read		= afs_issue_read,
 };

fs/ceph/addr.c

@@ -386,7 +386,7 @@ static void ceph_netfs_free_request(struct netfs_io_request *rreq)
 const struct netfs_request_ops ceph_netfs_ops = {
 	.init_request		= ceph_init_request,
 	.free_request		= ceph_netfs_free_request,
-	.begin_cache_operation	= ceph_begin_cache_operation,
+	.begin_cache_operation	= fscache_begin_cache_operation,
 	.issue_read		= ceph_netfs_issue_read,
 	.expand_readahead	= ceph_netfs_expand_readahead,
 	.clamp_length		= ceph_netfs_clamp_length,

fs/ceph/cache.h

@@ -57,13 +57,6 @@ static inline int ceph_fscache_dirty_folio(struct address_space *mapping,
 	return fscache_dirty_folio(mapping, folio, ceph_fscache_cookie(ci));
 }
 
-static inline int ceph_begin_cache_operation(struct netfs_io_request *rreq)
-{
-	struct fscache_cookie *cookie = ceph_fscache_cookie(ceph_inode(rreq->inode));
-
-	return fscache_begin_read_operation(&rreq->cache_resources, cookie);
-}
-
 static inline bool ceph_is_cache_enabled(struct inode *inode)
 {
 	return fscache_cookie_enabled(ceph_fscache_cookie(ceph_inode(inode)));
@@ -135,11 +128,6 @@ static inline bool ceph_is_cache_enabled(struct inode *inode)
 	return false;
 }
 
-static inline int ceph_begin_cache_operation(struct netfs_io_request *rreq)
-{
-	return -ENOBUFS;
-}
-
 static inline void ceph_fscache_note_page_release(struct inode *inode)
 {
 }

fs/fscache/io.c

@@ -158,6 +158,47 @@ int __fscache_begin_write_operation(struct netfs_cache_resources *cres,
 }
 EXPORT_SYMBOL(__fscache_begin_write_operation);
 
+/**
+ * fscache_begin_cache_operation - Begin a cache op for netfslib
+ * @rreq: The netfs request that wants to access the cache.
+ *
+ * Begin an I/O operation on behalf of the netfs helper library, read or write.
+ * @rreq indicates the netfs operation that wishes to access the cache.
+ *
+ * This is intended to be pointed to directly by the ->begin_cache_operation()
+ * netfs lib operation for the network filesystem.
+ *
+ * @cres->inval_counter is set from @cookie->inval_counter for comparison at
+ * the end of the operation.  This allows invalidation during the operation to
+ * be detected by the caller.
+ *
+ * Returns:
+ * * 0		- Success
+ * * -ENOBUFS	- No caching available
+ * * Other error code from the cache, such as -ENOMEM.
+ */
+int fscache_begin_cache_operation(struct netfs_io_request *rreq)
+{
+	switch (rreq->origin) {
+	case NETFS_READAHEAD:
+	case NETFS_READPAGE:
+	case NETFS_READ_FOR_WRITE:
+		return fscache_begin_operation(&rreq->cache_resources,
+					       netfs_i_cookie(rreq->inode),
+					       FSCACHE_WANT_PARAMS,
+					       fscache_access_io_read);
+	case NETFS_WRITEBACK:
+		return fscache_begin_operation(&rreq->cache_resources,
+					       netfs_i_cookie(rreq->inode),
+					       FSCACHE_WANT_PARAMS,
+					       fscache_access_io_write);
+	case NETFS_DIO_READ:
+	case NETFS_DIO_WRITE:
+	default:
+		return -ENOBUFS;
+	}
+}
+
 /**
  * fscache_dirty_folio - Mark folio dirty and pin a cache object for writeback
  * @mapping: The mapping the folio belongs to.

include/linux/fscache.h

@@ -175,6 +175,12 @@ extern void __fscache_write_to_cache(struct fscache_cookie *, struct address_spa
 				     bool);
 extern void __fscache_clear_page_bits(struct address_space *, loff_t, size_t);
 
+#if __fscache_available
+extern int fscache_begin_cache_operation(struct netfs_io_request *rreq);
+#else
+#define fscache_begin_cache_operation NULL
+#endif
+
 /**
  * fscache_acquire_volume - Register a volume as desiring caching services
  * @volume_key: An identification string for the volume