Linux Memory Mapping--mmap kernel 2.6
近几天有个项目需要实现用户层与内核共享内存。在前几篇博客中找到的均是kernel2.4 的。实现过程中，改的痛苦。对kernel源码才，勉强搞定。
后来在此网站(http://www.scs.ch/~frey/linux/memorymap.html)发现原来有一个demo:
#include <linux/config.h>
#include <linux/version.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
#ifdef MODVERSIONS
# include <linux/modversions.h>
#endif
#include <asm/io.h>
/* character device structures */
static dev_t mmap_dev;
static struct cdev mmap_cdev;
/* methods of the character device */
static int mmap_open(struct inode *inode, struct file *filp);
static int mmap_release(struct inode *inode, struct file *filp);
static int mmap_mmap(struct file *filp, struct vm_area_struct *vma);
/* the file operations, i.e. all character device methods */
static struct file_operations mmap_fops = {
.open = mmap_open,
.release = mmap_release,
.mmap = mmap_mmap,
.owner = THIS_MODULE,
};
// internal data
// length of the two memory areas
#define NPAGES 16
// pointer to the vmalloc'd area - alway page aligned
static int *vmalloc_area;
// pointer to the kmalloc'd area, rounded up to a page boundary
static int *kmalloc_area;
// original pointer for kmalloc'd area as returned by kmalloc
static void *kmalloc_ptr;
/* character device open method */
static int mmap_open(struct inode *inode, struct file *filp)
{
return 0;
}
/* character device last close method */
static int mmap_release(struct inode *inode, struct file *filp)
{
return 0;
}
// helper function, mmap's the kmalloc'd area which is physically contiguous
int mmap_kmem(struct file *filp, struct vm_area_struct *vma)
{
int ret;
long length = vma->vm_end - vma->vm_start;
/* check length - do not allow larger mappings than the number of
pages allocated */
if (length > NPAGES * PAGE_SIZE)
return -EIO;
/* map the whole physically contiguous area in one piece */
if ((ret = remap_pfn_range(vma,
vma->vm_start,
virt_to_phys((void *)kmalloc_area) >> PAGE_SHIFT,
length,
vma->vm_page_prot)) < 0) {
return ret;
}
return 0;
}
// helper function, mmap's the vmalloc'd area which is not physically contiguous
int mmap_vmem(struct file *filp, struct vm_area_struct *vma)
{
int ret;
long length = vma->vm_end - vma->vm_start;
unsigned long start = vma->vm_start;
char *vmalloc_area_ptr = (char *)vmalloc_area;
unsigned long pfn;
/* check length - do not allow larger mappings than the number of
pages allocated */
if (length > NPAGES * PAGE_SIZE)
return -EIO;
/* loop over all pages, map it page individually */
while (length > 0) {
pfn = vmalloc_to_pfn(vmalloc_area_ptr);
if ((ret = remap_pfn_range(vma, start, pfn, PAGE_SIZE,
PAGE_SHARED)) < 0) {
return ret;
}
start += PAGE_SIZE;
vmalloc_area_ptr += PAGE_SIZE;
length -= PAGE_SIZE;
}
return 0;
}
/* character device mmap method */
static int mmap_mmap(struct file *filp, struct vm_area_struct *vma)
{
/* at offset 0 we map the vmalloc'd area */
if (vma->vm_pgoff == 0) {
return mmap_vmem(filp, vma);
}
/* at offset NPAGES we map the kmalloc'd area */
if (vma->vm_pgoff == NPAGES) {
return mmap_kmem(filp, vma);
}
/* at any other offset we return an error */
return -EIO;
}
/* module initialization - called at module load time */
static int __init mmap_init(void)
{
int ret = 0;
int i;
/* allocate a memory area with kmalloc. Will be rounded up to a page boundary */
if ((kmalloc_ptr = kmalloc((NPAGES + 2) * PAGE_SIZE, GFP_KERNEL)) == NULL) {
ret = -ENOMEM;
goto out;
}
/* round it up to the page bondary */
kmalloc_area = (int *)((((unsigned long)kmalloc_ptr) + PAGE_SIZE - 1) & PAGE_MASK);
/* allocate a memory area with vmalloc. */
if ((vmalloc_area = (int *)vmalloc(NPAGES * PAGE_SIZE)) == NULL) {
ret = -ENOMEM;
goto out_kfree;
}
/* get the major number of the character device */
if ((ret = alloc_chrdev_region(&mmap_dev, 0, 1, "mmap")) < 0) {
printk(KERN_ERR "could not allocate major number for mmap\n");
goto out_vfree;
}
/* initialize the device structure and register the device with the kernel */
cdev_init(&mmap_cdev, &mmap_fops);
if ((ret = cdev_add(&mmap_cdev, mmap_dev, 1)) < 0) {
printk(KERN_ERR "could not allocate chrdev for mmap\n");
goto out_unalloc_region;
}
/* mark the pages reserved */
for (i = 0; i < NPAGES * PAGE_SIZE; i+= PAGE_SIZE) {
SetPageReserved(vmalloc_to_page((void *)(((unsigned long)vmalloc_area) + i)));
SetPageReserved(virt_to_page(((unsigned long)kmalloc_area) + i));
}
/* store a pattern in the memory - the test application will check for it */
for (i = 0; i < (NPAGES * PAGE_SIZE / sizeof(int)); i += 2) {
vmalloc_area[i] = (0xaffe << 16) + i;
vmalloc_area[i + 1] = (0xbeef << 16) + i;
kmalloc_area[i] = (0xdead << 16) + i;
kmalloc_area[i + 1] = (0xbeef << 16) + i;
}
return ret;
out_unalloc_region:
unregister_chrdev_region(mmap_dev, 1);
out_vfree:
vfree(vmalloc_area);
out_kfree:
kfree(kmalloc_ptr);
out:
return ret;
}
/* module unload */
static void __exit mmap_exit(void)
{
int i;
/* remove the character deivce */
cdev_del(&mmap_cdev);
unregister_chrdev_region(mmap_dev, 1);
/* unreserve the pages */
for (i = 0; i < NPAGES * PAGE_SIZE; i+= PAGE_SIZE) {
SetPageReserved(vmalloc_to_page((void *)(((unsigned long)vmalloc_area) + i)));
SetPageReserved(virt_to_page(((unsigned long)kmalloc_area) + i));
}
/* free the memory areas */
vfree(vmalloc_area);
kfree(kmalloc_ptr);
}
module_init(mmap_init);
module_exit(mmap_exit);
MODULE_DESCRIPTION("mmap demo driver");
MODULE_AUTHOR("Martin Frey <[email protected]>");
MODULE_LICENSE("BSD");