netfs: Add a netfs inode context

Add a netfs_i_context struct that should be included in the network
filesystem's own inode struct wrapper, directly after the VFS's inode
struct, e.g.:

	struct my_inode {
		struct {
			/* These must be contiguous */
			struct inode		vfs_inode;
			struct netfs_i_context	netfs_ctx;
		};
	};

The netfs_i_context struct so far contains a single field for the network
filesystem to use - the cache cookie:

	struct netfs_i_context {
		...
		struct fscache_cookie	*cache;
	};

Three functions are provided to help with this:

 (1) void netfs_i_context_init(struct inode *inode,
			       const struct netfs_request_ops *ops);

     Initialise the netfs context and set the operations.

 (2) struct netfs_i_context *netfs_i_context(struct inode *inode);

     Find the netfs context from the VFS inode.

 (3) struct inode *netfs_inode(struct netfs_i_context *ctx);

     Find the VFS inode from the netfs context.

Changes
=======
ver #4)
 - Fix netfs_is_cache_enabled() to check cookie->cache_priv to see if a
   cache is present[3].
 - Fix netfs_skip_folio_read() to zero out all of the page, not just some
   of it[3].

ver #3)
 - Split out the bit to move ceph cap-getting on readahead into
   ceph_init_request()[1].
 - Stick in a comment to the netfs inode structs indicating the contiguity
   requirements[2].

ver #2)
 - Adjust documentation to match.
 - Use "#if IS_ENABLED()" in netfs_i_cookie(), not "#ifdef".
 - Move the cap check from ceph_readahead() to ceph_init_request() to be
   called from netfslib.
 - Remove ceph_readahead() and use  netfs_readahead() directly instead.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com

Link: https://lore.kernel.org/r/8af0d47f17d89c06bbf602496dd845f2b0bf25b3.camel@kernel.org/ [1]
Link: https://lore.kernel.org/r/beaf4f6a6c2575ed489adb14b257253c868f9a5c.camel@kernel.org/ [2]
Link: https://lore.kernel.org/r/3536452.1647421585@warthog.procyon.org.uk/ [3]
Link: https://lore.kernel.org/r/164622984545.3564931.15691742939278418580.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/164678213320.1200972.16807551936267647470.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/164692909854.2099075.9535537286264248057.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/306388.1647595110@warthog.procyon.org.uk/ # v4

1 files changed, 16 insertions, 2 deletions

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 89837e904fa7..54c761bcc8e6 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -6,6 +6,7 @@
  */
 
 #include <linux/netfs.h>
+#include <linux/fscache.h>
 #include <trace/events/netfs.h>
 
 #ifdef pr_fmt
@@ -19,8 +20,6 @@
  */
 struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 					     struct file *file,
-					     const struct netfs_request_ops *ops,
-					     void *netfs_priv,
 					     loff_t start, size_t len,
 					     enum netfs_io_origin origin);
 void netfs_get_request(struct netfs_io_request *rreq, enum netfs_rreq_ref_trace what);
@@ -81,6 +80,21 @@ static inline void netfs_stat_d(atomic_t *stat)
 #define netfs_stat_d(x) do {} while(0)
 #endif
 
+/*
+ * Miscellaneous functions.
+ */
+static inline bool netfs_is_cache_enabled(struct netfs_i_context *ctx)
+{
+#if IS_ENABLED(CONFIG_FSCACHE)
+	struct fscache_cookie *cookie = ctx->cache;
+
+	return fscache_cookie_valid(cookie) && cookie->cache_priv &&
+		fscache_cookie_enabled(cookie);
+#else
+	return false;
+#endif
+}
+
 /*****************************************************************************/
 /*
  * debug tracing