Merge tag 'netfs-prep-20220318' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull netfs updates from David Howells:
 "Netfs prep for write helpers.

  Having had a go at implementing write helpers and content encryption
  support in netfslib, it seems that the netfs_read_{,sub}request
  structs and the equivalent write request structs were almost the same
  and so should be merged, thereby requiring only one set of
  alloc/get/put functions and a common set of tracepoints.

  Merging the structs also has the advantage that if a bounce buffer is
  added to the request struct, a read operation can be performed to fill
  the bounce buffer, the contents of the buffer can be modified and then
  a write operation can be performed on it to send the data wherever it
  needs to go using the same request structure all the way through. The
  I/O handlers would then transparently perform any required crypto.
  This should make it easier to perform RMW cycles if needed.

  The potentially common functions and structs, however, by their names
  all proclaim themselves to be associated with the read side of things.

  The bulk of these changes alter this in the following ways:

   - Rename struct netfs_read_{,sub}request to netfs_io_{,sub}request.

   - Rename some enums, members and flags to make them more appropriate.

   - Adjust some comments to match.

   - Drop "read"/"rreq" from the names of common functions. For
     instance, netfs_get_read_request() becomes netfs_get_request().

   - The ->init_rreq() and ->issue_op() methods become ->init_request()
     and ->issue_read(). I've kept the latter as a read-specific
     function and in another branch added an ->issue_write() method.

  The driver source is then reorganised into a number of files:

        fs/netfs/buffered_read.c        Create read reqs to the pagecache
        fs/netfs/io.c                   Dispatchers for read and write reqs
        fs/netfs/main.c                 Some general miscellaneous bits
        fs/netfs/objects.c              Alloc, get and put functions
        fs/netfs/stats.c                Optional procfs statistics.

  and future development can be fitted into this scheme, e.g.:

        fs/netfs/buffered_write.c       Modify the pagecache
        fs/netfs/buffered_flush.c       Writeback from the pagecache
        fs/netfs/direct_read.c          DIO read support
        fs/netfs/direct_write.c         DIO write support
        fs/netfs/unbuffered_write.c     Write modifications directly back

  Beyond the above changes, there are also some changes that affect how
  things work:

   - Make fscache_end_operation() generally available.

   - In the netfs tracing header, generate enums from the symbol ->
     string mapping tables rather than manually coding them.

   - Add a struct for filesystems that uses netfslib to put into their
     inode wrapper structs to hold extra state that netfslib is
     interested in, such as the fscache cookie. This allows netfslib
     functions to be set in filesystem operation tables and jumped to
     directly without having to have a filesystem wrapper.

   - Add a member to the struct added above to track the remote inode
     length as that may differ if local modifications are buffered. We
     may need to supply an appropriate EOF pointer when storing data (in
     AFS for example).

   - Pass extra information to netfs_alloc_request() so that the
     ->init_request() hook can access it and retain information to
     indicate the origin of the operation.

   - Make the ->init_request() hook return an error, thereby allowing a
     filesystem that isn't allowed to cache an inode (ceph or cifs, for
     example) to skip readahead.

   - Switch to using refcount_t for subrequests and add tracepoints to
     log refcount changes for the request and subrequest structs.

   - Add a function to consolidate dispatching a read request. Similar
     code is used in three places and another couple are likely to be
     added in the future"

Link: https://lore.kernel.org/all/2639515.1648483225@warthog.procyon.org.uk/

* tag 'netfs-prep-20220318' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  afs: Maintain netfs_i_context::remote_i_size
  netfs: Keep track of the actual remote file size
  netfs: Split some core bits out into their own file
  netfs: Split fs/netfs/read_helper.c
  netfs: Rename read_helper.c to io.c
  netfs: Prepare to split read_helper.c
  netfs: Add a function to consolidate beginning a read
  netfs: Add a netfs inode context
  ceph: Make ceph_init_request() check caps on readahead
  netfs: Change ->init_request() to return an error code
  netfs: Refactor arguments for netfs_alloc_read_request
  netfs: Adjust the netfs_failure tracepoint to indicate non-subreq lines
  netfs: Trace refcounting on the netfs_io_subrequest struct
  netfs: Trace refcounting on the netfs_io_request struct
  netfs: Adjust the netfs_rreq tracepoint slightly
  netfs: Split netfs_io_* object handling out
  netfs: Finish off rename of netfs_read_request to netfs_io_request
  netfs: Rename netfs_read_*request to netfs_io_*request
  netfs: Generate enums from trace symbol mapping lists
  fscache: export fscache_end_operation()

1 files changed, 92 insertions, 48 deletions

diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst
index 4f373a8ec47b..69f00179fdfe 100644
--- a/Documentation/filesystems/netfs_library.rst
+++ b/Documentation/filesystems/netfs_library.rst
@@ -7,6 +7,8 @@ Network Filesystem Helper Library
 .. Contents:
 
  - Overview.
+ - Per-inode context.
+   - Inode context helper functions.
  - Buffered read helpers.
    - Read helper functions.
    - Read helper structures.
@@ -28,6 +30,69 @@ Note that the library module doesn't link against local caching directly, so
 access must be provided by the netfs.
 
 
+Per-Inode Context
+=================
+
+The network filesystem helper library needs a place to store a bit of state for
+its use on each netfs inode it is helping to manage.  To this end, a context
+structure is defined::
+
+	struct netfs_i_context {
+		const struct netfs_request_ops *ops;
+		struct fscache_cookie	*cache;
+	};
+
+A network filesystem that wants to use netfs lib must place one of these
+directly after the VFS ``struct inode`` it allocates, usually as part of its
+own struct.  This can be done in a way similar to the following::
+
+	struct my_inode {
+		struct {
+			/* These must be contiguous */
+			struct inode		vfs_inode;
+			struct netfs_i_context  netfs_ctx;
+		};
+		...
+	};
+
+This allows netfslib to find its state by simple offset from the inode pointer,
+thereby allowing the netfslib helper functions to be pointed to directly by the
+VFS/VM operation tables.
+
+The structure contains the following fields:
+
+ * ``ops``
+
+   The set of operations provided by the network filesystem to netfslib.
+
+ * ``cache``
+
+   Local caching cookie, or NULL if no caching is enabled.  This field does not
+   exist if fscache is disabled.
+
+
+Inode Context Helper Functions
+------------------------------
+
+To help deal with the per-inode context, a number helper functions are
+provided.  Firstly, a function to perform basic initialisation on a context and
+set the operations table pointer::
+
+	void netfs_i_context_init(struct inode *inode,
+				  const struct netfs_request_ops *ops);
+
+then two functions to cast between the VFS inode structure and the netfs
+context::
+
+	struct netfs_i_context *netfs_i_context(struct inode *inode);
+	struct inode *netfs_inode(struct netfs_i_context *ctx);
+
+and finally, a function to get the cache cookie pointer from the context
+attached to an inode (or NULL if fscache is disabled)::
+
+	struct fscache_cookie *netfs_i_cookie(struct inode *inode);
+
+
 Buffered Read Helpers
 =====================
 
@@ -70,38 +135,22 @@ Read Helper Functions
 
 Three read helpers are provided::
 
-	void netfs_readahead(struct readahead_control *ractl,
-			     const struct netfs_read_request_ops *ops,
-			     void *netfs_priv);
+	void netfs_readahead(struct readahead_control *ractl);
 	int netfs_readpage(struct file *file,
-			   struct folio *folio,
-			   const struct netfs_read_request_ops *ops,
-			   void *netfs_priv);
+			   struct page *page);
 	int netfs_write_begin(struct file *file,
 			      struct address_space *mapping,
 			      loff_t pos,
 			      unsigned int len,
 			      unsigned int flags,
 			      struct folio **_folio,
-			      void **_fsdata,
-			      const struct netfs_read_request_ops *ops,
-			      void *netfs_priv);
-
-Each corresponds to a VM operation, with the addition of a couple of parameters
-for the use of the read helpers:
+			      void **_fsdata);
 
- * ``ops``
-
-   A table of operations through which the helpers can talk to the filesystem.
-
- * ``netfs_priv``
+Each corresponds to a VM address space operation.  These operations use the
+state in the per-inode context.
 
-   Filesystem private data (can be NULL).
-
-Both of these values will be stored into the read request structure.
-
-For ->readahead() and ->readpage(), the network filesystem should just jump
-into the corresponding read helper; whereas for ->write_begin(), it may be a
+For ->readahead() and ->readpage(), the network filesystem just point directly
+at the corresponding read helper; whereas for ->write_begin(), it may be a
 little more complicated as the network filesystem might want to flush
 conflicting writes or track dirty data and needs to put the acquired folio if
 an error occurs after calling the helper.
@@ -116,7 +165,7 @@ occurs, the request will get partially completed if sufficient data is read.
 
 Additionally, there is::
 
-  * void netfs_subreq_terminated(struct netfs_read_subrequest *subreq,
+  * void netfs_subreq_terminated(struct netfs_io_subrequest *subreq,
 				 ssize_t transferred_or_error,
 				 bool was_async);
 
@@ -132,7 +181,7 @@ Read Helper Structures
 The read helpers make use of a couple of structures to maintain the state of
 the read.  The first is a structure that manages a read request as a whole::
 
-	struct netfs_read_request {
+	struct netfs_io_request {
 		struct inode		*inode;
 		struct address_space	*mapping;
 		struct netfs_cache_resources cache_resources;
@@ -140,7 +189,7 @@ the read.  The first is a structure that manages a read request as a whole::
 		loff_t			start;
 		size_t			len;
 		loff_t			i_size;
-		const struct netfs_read_request_ops *netfs_ops;
+		const struct netfs_request_ops *netfs_ops;
 		unsigned int		debug_id;
 		...
 	};
@@ -187,8 +236,8 @@ The above fields are the ones the netfs can use.  They are:
 The second structure is used to manage individual slices of the overall read
 request::
 
-	struct netfs_read_subrequest {
-		struct netfs_read_request *rreq;
+	struct netfs_io_subrequest {
+		struct netfs_io_request *rreq;
 		loff_t			start;
 		size_t			len;
 		size_t			transferred;
@@ -244,32 +293,26 @@ Read Helper Operations
 The network filesystem must provide the read helpers with a table of operations
 through which it can issue requests and negotiate::
 
-	struct netfs_read_request_ops {
-		void (*init_rreq)(struct netfs_read_request *rreq, struct file *file);
-		bool (*is_cache_enabled)(struct inode *inode);
-		int (*begin_cache_operation)(struct netfs_read_request *rreq);
-		void (*expand_readahead)(struct netfs_read_request *rreq);
-		bool (*clamp_length)(struct netfs_read_subrequest *subreq);
-		void (*issue_op)(struct netfs_read_subrequest *subreq);
-		bool (*is_still_valid)(struct netfs_read_request *rreq);
+	struct netfs_request_ops {
+		void (*init_request)(struct netfs_io_request *rreq, struct file *file);
+		int (*begin_cache_operation)(struct netfs_io_request *rreq);
+		void (*expand_readahead)(struct netfs_io_request *rreq);
+		bool (*clamp_length)(struct netfs_io_subrequest *subreq);
+		void (*issue_read)(struct netfs_io_subrequest *subreq);
+		bool (*is_still_valid)(struct netfs_io_request *rreq);
 		int (*check_write_begin)(struct file *file, loff_t pos, unsigned len,
 					 struct folio *folio, void **_fsdata);
-		void (*done)(struct netfs_read_request *rreq);
+		void (*done)(struct netfs_io_request *rreq);
 		void (*cleanup)(struct address_space *mapping, void *netfs_priv);
 	};
 
 The operations are as follows:
 
- * ``init_rreq()``
+ * ``init_request()``
 
    [Optional] This is called to initialise the request structure.  It is given
    the file for reference and can modify the ->netfs_priv value.
 
- * ``is_cache_enabled()``
-
-   [Required] This is called by netfs_write_begin() to ask if the file is being
-   cached.  It should return true if it is being cached and false otherwise.
-
  * ``begin_cache_operation()``
 
    [Optional] This is called to ask the network filesystem to call into the
@@ -305,7 +348,7 @@ The operations are as follows:
 
    This should return 0 on success and an error code on error.
 
- * ``issue_op()``
+ * ``issue_read()``
 
    [Required] The helpers use this to dispatch a subrequest to the server for
    reading.  In the subrequest, ->start, ->len and ->transferred indicate what
@@ -420,12 +463,12 @@ The network filesystem's ->begin_cache_operation() method is called to set up a
 cache and this must call into the cache to do the work.  If using fscache, for
 example, the cache would call::
 
-	int fscache_begin_read_operation(struct netfs_read_request *rreq,
+	int fscache_begin_read_operation(struct netfs_io_request *rreq,
 					 struct fscache_cookie *cookie);
 
 passing in the request pointer and the cookie corresponding to the file.
 
-The netfs_read_request object contains a place for the cache to hang its
+The netfs_io_request object contains a place for the cache to hang its
 state::
 
 	struct netfs_cache_resources {
@@ -443,7 +486,7 @@ operation table looks like the following::
 		void (*expand_readahead)(struct netfs_cache_resources *cres,
 					 loff_t *_start, size_t *_len, loff_t i_size);
 
-		enum netfs_read_source (*prepare_read)(struct netfs_read_subrequest *subreq,
+		enum netfs_io_source (*prepare_read)(struct netfs_io_subrequest *subreq,
 						       loff_t i_size);
 
 		int (*read)(struct netfs_cache_resources *cres,
@@ -562,4 +605,5 @@ API Function Reference
 ======================
 
 .. kernel-doc:: include/linux/netfs.h
-.. kernel-doc:: fs/netfs/read_helper.c
+.. kernel-doc:: fs/netfs/buffered_read.c
+.. kernel-doc:: fs/netfs/io.c