[RFC 06/19] netfs: add type field to struct netfs_read_request

[Jeffle Xu <jefflexu@linux.alibaba.com>]

fscache/cachefiles used to serve as a local cache for remote fs.
This patch set introduces a new use case, in which local read-only
fs could implement demand read with fscache.

Thus 'type' field is used to distinguish which mode netfs API works in.

Besides, in demand-read case, local fs using fscache for demand-read
can't offer and also doesn't need the file handle of the netfs file. The
input folio of netfs_readpage() is may not a page cache inside the
address space of the netfs file, and may be just a temporary page
containing the data. What netfs API needs to do is just move data from
backing file the the input folio. Thus buffer the folio in 'struct
netfs_read_request'.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 include/linux/netfs.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index b46c39d98bbd..638ea5d63869 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -148,6 +148,11 @@ struct netfs_read_subrequest {
 #define NETFS_SREQ_NO_PROGRESS		4	/* Set if we didn't manage to read any data */
 };
 
+enum netfs_read_request_type {
+	NETFS_TYPE_CACHE,
+	NETFS_TYPE_DEMAND,
+};
+
 /*
  * Descriptor for a read helper request.  This is used to make multiple I/O
  * requests on a variety of sources and then stitch the result together.
@@ -156,6 +161,7 @@ struct netfs_read_request {
 	struct work_struct	work;
 	struct inode		*inode;		/* The file being accessed */
 	struct address_space	*mapping;	/* The mapping being accessed */
+	struct folio		*folio;
 	struct netfs_cache_resources cache_resources;
 	struct list_head	subrequests;	/* Requests to fetch I/O from disk or net */
 	void			*netfs_priv;	/* Private data for the netfs */
@@ -177,6 +183,7 @@ struct netfs_read_request {
 #define NETFS_RREQ_FAILED		4	/* The request failed */
 #define NETFS_RREQ_IN_PROGRESS		5	/* Unlocked when the request completes */
 	const struct netfs_read_request_ops *netfs_ops;
+	enum netfs_read_request_type type;
 };
 
 /*
-- 
2.27.0