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/*
* Copyright (c) 2003-2009 Erez Zadok
* Copyright (c) 2003-2006 Charles P. Wright
* Copyright (c) 2005-2007 Josef 'Jeff' Sipek
* Copyright (c) 2005-2006 Junjiro Okajima
* Copyright (c) 2006 Shaya Potter
* Copyright (c) 2005 Arun M. Krishnakumar
* Copyright (c) 2004-2006 David P. Quigley
* Copyright (c) 2003-2004 Mohammad Nayyer Zubair
* Copyright (c) 2003 Puja Gupta
* Copyright (c) 2003 Harikesavan Krishnan
* Copyright (c) 2003-2009 Stony Brook University
* Copyright (c) 2003-2009 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 "union.h"
/*
* XXX: we need a dummy readpage handler because generic_file_mmap (which we
* use in unionfs_mmap) checks for the existence of
* mapping->a_ops->readpage, else it returns -ENOEXEC. The VFS will need to
* be fixed to allow a file system to define vm_ops->fault without any
* address_space_ops whatsoever.
*
* Otherwise, we don't want to use our readpage method at all.
*/
static int unionfs_readpage(struct file *file, struct page *page)
{
BUG();
return -EINVAL;
}
static int unionfs_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
int err;
struct file *file, *lower_file;
struct vm_operations_struct *lower_vm_ops;
struct vm_area_struct lower_vma;
BUG_ON(!vma);
memcpy(&lower_vma, vma, sizeof(struct vm_area_struct));
file = lower_vma.vm_file;
lower_vm_ops = UNIONFS_F(file)->lower_vm_ops;
BUG_ON(!lower_vm_ops);
lower_file = unionfs_lower_file(file);
BUG_ON(!lower_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 unionfs_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 unionfs 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.
*/
struct address_space_operations unionfs_aops = {
/* empty on purpose */
};
/*
* XXX: we need a second, dummy address_space_ops vector, to be used
* temporarily during unionfs_mmap, because the latter calls
* generic_file_mmap, which checks if ->readpage exists, else returns
* -ENOEXEC.
*/
struct address_space_operations unionfs_dummy_aops = {
.readpage = unionfs_readpage,
};
struct vm_operations_struct unionfs_vm_ops = {
.fault = unionfs_fault,
};
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