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()

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