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/* -*- C -*-
* mmap.c -- memory mapping for the scullp char module
*
* Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
* Copyright (C) 2001 O'Reilly & Associates
*
* The source code in this file can be freely used, adapted,
* and redistributed in source or binary form, so long as an
* acknowledgment appears in derived source files. The citation
* should list that the code comes from the book "Linux Device
* Drivers" by Alessandro Rubini and Jonathan Corbet, published
* by O'Reilly & Associates. No warranty is attached;
* we cannot take responsibility for errors or fitness for use.
*
* $Id: _mmap.c.in,v 1.13 2004/10/18 18:07:36 corbet Exp $
*/
#include <linux/module.h>
#include <linux/mm.h> /* everything */
#include <linux/errno.h> /* error codes */
#include <asm/pgtable.h>
#include "scullp.h" /* local definitions */
/*
* open and close: just keep track of how many times the device is
* mapped, to avoid releasing it.
*/
void scullp_vma_open(struct vm_area_struct *vma)
{
struct scullp_dev *dev = vma->vm_private_data;
dev->vmas++;
}
void scullp_vma_close(struct vm_area_struct *vma)
{
struct scullp_dev *dev = vma->vm_private_data;
dev->vmas--;
}
/*
* The nopage method: the core of the file. It retrieves the
* page required from the scullp device and returns it to the
* user. The count for the page must be incremented, because
* it is automatically decremented at page unmap.
*
* For this reason, "order" must be zero. Otherwise, only the first
* page has its count incremented, and the allocating module must
* release it as a whole block. Therefore, it isn't possible to map
* pages from a multipage block: when they are unmapped, their count
* is individually decreased, and would drop to 0.
*/
struct page *scullp_vma_nopage(struct vm_area_struct *vma,
unsigned long address, int *type)
{
unsigned long offset;
struct scullp_dev *ptr, *dev = vma->vm_private_data;
struct page *page = NOPAGE_SIGBUS;
void *pageptr = NULL; /* default to "missing" */
down(&dev->sem);
offset = (address - vma->vm_start) + (vma->vm_pgoff << PAGE_SHIFT);
if (offset >= dev->size) goto out; /* out of range */
/*
* Now retrieve the scullp device from the list,then the page.
* If the device has holes, the process receives a SIGBUS when
* accessing the hole.
*/
offset >>= PAGE_SHIFT; /* offset is a number of pages */
for (ptr = dev; ptr && offset >= dev->qset;) {
ptr = ptr->next;
offset -= dev->qset;
}
if (ptr && ptr->data) pageptr = ptr->data[offset];
if (!pageptr) goto out; /* hole or end-of-file */
page = virt_to_page(pageptr);
/* got it, now increment the count */
get_page(page);
if (type)
*type = VM_FAULT_MINOR;
out:
up(&dev->sem);
return page;
}
struct vm_operations_struct scullp_vm_ops = {
.open = scullp_vma_open,
.close = scullp_vma_close,
.nopage = scullp_vma_nopage,
};
int scullp_mmap(struct file *filp, struct vm_area_struct *vma)
{
struct inode *inode = filp->f_dentry->d_inode;
/* refuse to map if order is not 0 */
if (scullp_devices[iminor(inode)].order)
return -ENODEV;
/* don't do anything here: "nopage" will set up page table entries */
vma->vm_ops = &scullp_vm_ops;
vma->vm_flags |= VM_RESERVED;
vma->vm_private_data = filp->private_data;
scullp_vma_open(vma);
return 0;
}
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