cifs: Implement netfslib hooks

Provide implementation of the netfslib hooks that will be used by netfslib
to ask cifs to set up and perform operations.  Of particular note are

 (*) cifs_clamp_length() - This is used to negotiate the size of the next
     subrequest in a read request, taking into account the credit available
     and the rsize.  The credits are attached to the subrequest.

 (*) cifs_req_issue_read() - This is used to issue a subrequest that has
     been set up and clamped.

 (*) cifs_prepare_write() - This prepares to fill a subrequest by picking a
     channel, reopening the file and requesting credits so that we can set
     the maximum size of the subrequest and also sets the maximum number of
     segments if we're doing RDMA.

 (*) cifs_issue_write() - This releases any unneeded credits and issues an
     asynchronous data write for the contiguous slice of file covered by
     the subrequest.  This should possibly be folded in to all
     ->async_writev() ops and that called directly.

 (*) cifs_begin_writeback() - This gets the cached writable handle through
     which we do writeback (this does not affect writethrough, unbuffered
     or direct writes).

At this point, cifs is not wired up to actually *use* netfslib; that will
be done in a subsequent patch.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

fs/netfs/buffered_write.c

@@ -405,6 +405,9 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 	} while (iov_iter_count(iter));
 
 out:
+	if (likely(written) && ctx->ops->post_modify)
+		ctx->ops->post_modify(inode);
+
 	if (unlikely(wreq)) {
 		ret2 = netfs_end_writethrough(wreq, &wbc, writethrough);
 		wbc_detach_inode(&wbc);
@@ -521,6 +524,7 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
 	struct folio *folio = page_folio(vmf->page);
 	struct file *file = vmf->vma->vm_file;
 	struct inode *inode = file_inode(file);
+	struct netfs_inode *ictx = netfs_inode(inode);
 	vm_fault_t ret = VM_FAULT_RETRY;
 	int err;
 
@@ -567,6 +571,8 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
 		trace_netfs_folio(folio, netfs_folio_trace_mkwrite);
 	netfs_set_group(folio, netfs_group);
 	file_update_time(file);
+	if (ictx->ops->post_modify)
+		ictx->ops->post_modify(inode);
 	ret = VM_FAULT_LOCKED;
 out:
 	sb_end_pagefault(inode->i_sb);

fs/smb/client/Kconfig

@@ -2,6 +2,7 @@
 config CIFS
 	tristate "SMB3 and CIFS support (advanced network filesystem)"
 	depends on INET
+	select NETFS_SUPPORT
 	select NLS
 	select NLS_UCS2_UTILS
 	select CRYPTO

fs/smb/client/cifsfs.c

@@ -1758,7 +1758,7 @@ static int cifs_init_netfs(void)
 {
 	cifs_io_request_cachep =
 		kmem_cache_create("cifs_io_request",
-				  sizeof(struct netfs_io_request), 0,
+				  sizeof(struct cifs_io_request), 0,
 				  SLAB_HWCACHE_ALIGN, NULL);
 	if (!cifs_io_request_cachep)
 		goto nomem_req;

fs/smb/client/cifsfs.h

@@ -84,6 +84,7 @@ extern const struct inode_operations cifs_namespace_inode_operations;
 
 
 /* Functions related to files and directories */
+extern const struct netfs_request_ops cifs_req_ops;
 extern const struct file_operations cifs_file_ops;
 extern const struct file_operations cifs_file_direct_ops; /* if directio mnt */
 extern const struct file_operations cifs_file_strict_ops; /* if strictio mnt */

fs/smb/client/cifsglob.h

@@ -1491,31 +1491,41 @@ struct cifs_aio_ctx {
 	bool			direct_io;
 };
 
+struct cifs_io_request {
+	struct netfs_io_request		rreq;
+	struct cifsFileInfo		*cfile;
+};
+
 /* asynchronous read support */
 struct cifs_io_subrequest {
-	struct netfs_io_subrequest	subreq;
-	struct cifsFileInfo		*cfile;
-	struct address_space		*mapping;
-	struct cifs_aio_ctx		*ctx;
+	union {
+		struct netfs_io_subrequest subreq;
+		struct netfs_io_request *rreq;
+		struct cifs_io_request *req;
+	};
 	ssize_t				got_bytes;
 	pid_t				pid;
+	unsigned int			xid;
 	int				result;
+	bool				have_xid;
+	bool				replay;
 	struct kvec			iov[2];
 	struct TCP_Server_Info		*server;
 #ifdef CONFIG_CIFS_SMB_DIRECT
 	struct smbd_mr			*mr;
 #endif
 	struct cifs_credits		credits;
 
-	enum writeback_sync_modes	sync_mode;
-	bool				uncached;
-	bool				replay;
-	struct bio_vec			*bv;
-
 	// TODO: Remove following elements
 	struct list_head		list;
 	struct completion		done;
 	struct work_struct		work;
+	struct cifsFileInfo		*cfile;
+	struct address_space		*mapping;
+	struct cifs_aio_ctx		*ctx;
+	enum writeback_sync_modes	sync_mode;
+	bool				uncached;
+	struct bio_vec			*bv;
 };
 
 /*