zz用户和kernel空间使用mmap共享内存

时间：2009-05-25 来源：soararing

作者：http://jinglexy.cublog.cn
MSN: jinglexy at yahoo.com.cn
2008.06.04

原来的程序：

/* 文件操作 */
static struct file_operations xxx_fops = {
   ......
   .mmap       =   _xxxx_mmap,
   ......
};

static int _xxxx_mmap(struct file * file, struct vm_area_struct * vma)
{
   int offset;
   offset = ((int)(__pa(pdata)) >> PAGE_SHIFT);   // pdata是 __get_free_page得到的

   vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
   vma->vm_flags |= VM_RESERVED;

   printk("vma start: 0x%lx, buffer pfn: 0x%lx\n", vma->vm_start, offset);
   if (remap_pfn_range(vma, vma->vm_start,
               offset,
               vma->vm_end - vma->vm_start,
               vma->vm_page_prot))
       return -EAGAIN;

   return 0;
}

ldd3中讲到，对于常规内存，不能用remap_pfn_range，这个限制用来保证系统稳定性。
remap_pfn_range时候做外部io/mem空间映射。
所以上面的例子当然运行错误，改为nopage方式，如下（运行正常）：

/* 文件操作 */
static struct file_operations xxx_fops = {
   ......
   .mmap       =   _xxxx_mmap,
   ......
};

static int _xxxx_mmap(struct file * file, struct vm_area_struct * vma)
{
   vma->vm_ops = &scullv_vm_ops;
   vma->vm_flags |= VM_RESERVED;
   return 0;
}

struct page *scullv_vma_nopage(struct vm_area_struct *vma,
                                unsigned long address, int *type)
{
   struct page *page = NOPAGE_SIGBUS;

   if(pdata) {
       page = virt_to_page(pdata);   // get_free_page得到的内存不要用vmalloc_to_page
       get_page(page);
       if(type)
           *type = VM_FAULT_MINOR;
   }

   return page;
}

测试程序：
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/fcntl.h>
#include <sys/types.h>
#include <sys/mman.h>

int main(int argc, char *argv[])
{
   int fd;
   int *mp;
   int i = 0;

   if(-1 == (fd = open("/dev/testdev", O_RDWR)))
       return -1;

   mp = (int *)mmap(0, 4096, (PROT_WRITE | PROT_READ), MAP_SHARED, fd, 0);
   if(MAP_FAILED == mp) {
       printf("mmap failed\n");
       close(fd);
       return -2;
   }

   // success, r/w here
   while(1) {
       mp[0] = 4;
       mp[1] = 0x111 + i++;
       mp[2] = 0x222 + i++;
       mp[3] = 0x333 + i++;
       mp[4] = 0x444 + i++;
       sleep(1);
   }
   close(fd);

   return 0;
}

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