来源：天极网 发表时间：2006-10-28　【ovo.com.cn

下面的程序在启动的时候保留一段内存，然后使用ioremap将它映射到内核虚拟空间，同时又用remap_page_range映射到用户虚拟空间，这样一来，内核和用户都能访问。如果在内核虚拟地址将这段内存初始化串"abcd"，那么在用户虚拟地址能够读出来：

/************mmap_ioremap.c**************/ #include <linux/module.h> #include <linux/kernel.h> #include <linux/errno.h> #include <linux/mm.h> #include <linux/wrapper.h> /* for mem_map_(un)reserve */ #include <asm/io.h> /* for virt_to_phys */ #include <linux/slab.h> /* for kmalloc and kfree */ MODULE_PARM(mem_start, "i"); MODULE_PARM(mem_size, "i"); static int mem_start = 101, mem_size = 10; static char *reserve_virt_addr; static int major; int mmapdrv_open(struct inode *inode, struct file *file); int mmapdrv_release(struct inode *inode, struct file *file); int mmapdrv_mmap(struct file *file, struct vm_area_struct *vma); static struct file_operations mmapdrv_fops = { 　owner: THIS_MODULE, mmap: mmapdrv_mmap, open: mmapdrv_open, release: 　mmapdrv_release, }; int init_module(void) { 　if ((major = register_chrdev(0, "mmapdrv", &mmapdrv_fops)) < 0) 　{ 　　printk("mmapdrv: unable to register character device\n"); 　　return ( - EIO); 　} 　printk("mmap device major = %d\n", major); 　printk("high memory physical address 0x%ldM\n", virt_to_phys(high_memory) / 1024 / 1024); 　reserve_virt_addr = ioremap(mem_start *1024 * 1024, mem_size *1024 * 1024); 　printk("reserve_virt_addr = 0x%lx\n", (unsigned long)reserve_virt_addr); 　if (reserve_virt_addr) 　{ 　　int i; 　　for (i = 0; i < mem_size *1024 * 1024; i += 4) 　　{ 　　　reserve_virt_addr[i] = 'a'; 　　　reserve_virt_addr[i + 1] = 'b'; 　　　reserve_virt_addr[i + 2] = 'c'; 　　　reserve_virt_addr[i + 3] = 'd'; 　　} 　} 　else 　{ 　　unregister_chrdev(major, "mmapdrv"); 　　return - ENODEV; 　} 　return 0; } /* remove the module */ void cleanup_module(void) { 　if (reserve_virt_addr) 　　iounmap(reserve_virt_addr); 　unregister_chrdev(major, "mmapdrv"); 　return ; } int mmapdrv_open(struct inode *inode, struct file *file) { 　MOD_INC_USE_COUNT; 　return (0); } int mmapdrv_release(struct inode *inode, struct file *file) { 　MOD_DEC_USE_COUNT; 　return (0); } int mmapdrv_mmap(struct file *file, struct vm_area_struct *vma) { 　unsigned long offset = vma->vm_pgoff << PAGE_SHIFT; 　unsigned long size = vma->vm_end - vma->vm_start; 　if (size > mem_size *1024 * 1024) 　{ 　　printk("size too big\n"); 　　return ( - ENXIO); 　} 　offset = offset + mem_start * 1024 * 1024; 　/* we do not want to have this area swapped out, lock it */ 　vma->vm_flags |= VM_LOCKED; 　if (remap_page_range(vma, vma->vm_start, offset, size, PAGE_SHARED)) 　{ 　　printk("remap page range failed\n"); 　　return - ENXIO; 　} 　return (0); }

　　remap_page_range函数的功能是构造用于映射一段物理地址的新页表，实现了内核空间与用户空间的映射，其原型如下：

int remap_page_range(vma_area_struct *vma, unsigned long from, unsigned long to, unsigned long size, pgprot_tprot);

　　使用mmap最典型的例子是显示卡的驱动，将显存空间直接从内核映射到用户空间将可提供显存的读写效率。

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