Wrapfs: vm_ops operations

Includes necessary address_space workaround ops.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>

diff --git a/fs/wrapfs/mmap.c b/fs/wrapfs/mmap.c
new file mode 100644 (file)
index 0000000..0c72ef4
--- /dev/null
+++ b/fs/wrapfs/mmap.c
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 1998-2010 Erez Zadok
+ * Copyright (c) 2009     Shrikar Archak
+ * Copyright (c) 2003-2010 Stony Brook University
+ * Copyright (c) 2003-2010 The Research Foundation of SUNY
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include "wrapfs.h"
+
+static int wrapfs_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+       int err;
+       struct file *file, *lower_file;
+       const struct vm_operations_struct *lower_vm_ops;
+       struct vm_area_struct lower_vma;
+
+       memcpy(&lower_vma, vma, sizeof(struct vm_area_struct));
+       file = lower_vma.vm_file;
+       lower_vm_ops = WRAPFS_F(file)->lower_vm_ops;
+       BUG_ON(!lower_vm_ops);
+
+       lower_file = wrapfs_lower_file(file);
+       /*
+        * XXX: vm_ops->fault may be called in parallel.  Because we have to
+        * resort to temporarily changing the vma->vm_file to point to the
+        * lower file, a concurrent invocation of wrapfs_fault could see a
+        * different value.  In this workaround, we keep a different copy of
+        * the vma structure in our stack, so we never expose a different
+        * value of the vma->vm_file called to us, even temporarily.  A
+        * better fix would be to change the calling semantics of ->fault to
+        * take an explicit file pointer.
+        */
+       lower_vma.vm_file = lower_file;
+       err = lower_vm_ops->fault(&lower_vma, vmf);
+       return err;
+}
+
+/*
+ * XXX: the default address_space_ops for wrapfs is empty.  We cannot set
+ * our inode->i_mapping->a_ops to NULL because too many code paths expect
+ * the a_ops vector to be non-NULL.
+ */
+const struct address_space_operations wrapfs_aops = {
+       /* empty on purpose */
+};
+
+const struct vm_operations_struct wrapfs_vm_ops = {
+       .fault          = wrapfs_fault,
+};