1 files changed, 119 insertions, 0 deletions
diff --git a/scullp/mmap.c b/scullp/mmap.c
new file mode 100644
index 0000000..f5166db
--- /dev/null
+++ b/scullp/mmap.c
@@ -0,0 +1,119 @@
+/*  -*- 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/config.h>
+#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;
+}
+