Chinaunix

标题: 高手指点mmap实现问题 [打印本页]

---

作者: bin_linux96    时间: 2011-12-02 08:52
标题: 高手指点mmap实现问题
自己写了一个虚拟的字符设备/dev/test ，字符设备在内核中为一块内存(用kmalloc),
我想实现的功能是：先通过mmap函数把设备文件映射到用户空间，然后通过strncpy函数向设备写入数据，然后再通过read去读我写入的数据。
我的问题是：在用户空间中如设置mmap的参数：offset = 0;可以正常实现功能，也就是可以用read读出来，而当offset = 1024*4（4k倍数）时不能实现我想要的结果(用read读不出用strncpy写入的数据)。其他file_operations函数功能都可正常实现。

几个函数的原型如下
系统调用mmap : void *mmap(void *start, size_t length, int prot, int flags,int fd, off_t offset);

内核中mmap：int (*mmap)(struct file *filpstruct vm_area_struct *vma) ;

                      int remap_pfn_range(struct vm_area_struct *vma,unsigned long virt,unsigned long pfn,unsigned long size,pgprot_t prot)

用户空间测试代码如下：

1. #include<stdio.h>
   
2. #include<stdlib.h>
   
3. #include<sys/types.h>
   
4. #include<sys/stat.h>
   
5. #include<fcntl.h>
   
6. #include<sys/mman.h>
   
7. #include<string.h>
   
8. 
   
9. #define MAP_SIZE 1024*4*10
   
10. #define OFF_SET 1024*4
    
11. int main(void )
    
12. {
    
13.     int ret,fd ,new_fd ;
    
14.     int totalSize = 0 ;
    
15.     char cArray [512] = "22221111111111,2,3,4,5,6,7,8,9,a,b,c,d,e,f" ;
    
16.     char output [512] = {0} ;
    
17.     void * vir_addr = NULL ;
    
18. 
    
19.     fd = open("/dev/test",O_RDWR);
    
20.     if( fd<=0 ){
    
21.         printf("open file error \n");
    
22.         return -1 ;
    
23.     }
    
24. 
    
25.     vir_addr = mmap(NULL,MAP_SIZE,PROT_READ|PROT_WRITE,MAP_SHARED,fd,OFF_SET);
    
26.     if(NULL==vir_addr){
    
27.         printf("mmap error !!!\n");
    
28.         return -1 ;
    
29.     }
    
30.     printf("vir_addr = 0x%x \n",vir_addr);
    
31.     strncpy(vir_addr,cArray,512);
    
32.     lseek(fd,OFF_SET,SEEK_SET) [color=Red];//当OFF_SET 是4k的倍数时，不管要不要此句都不行。[/color]   
    
33.    int i = 0 ,c;
    
34.     for(i = 0;i<50;i++){
    
35.     read(fd,&c,1);
    
36.     printf("read result = %c\n",c);
    
37. 
    
38.     }
    
39. 
    
40.     close(new_fd) ;
    
41.     return 0;
    
42. }

复制代码

内核空间代码：

1. #include<linux/kernel.h>
   
2. #include<linux/init.h>
   
3. #include<linux/module.h>
   
4. //#include<linux/sched.h>
   
5. #include<linux/fs.h>
   
6. #include<linux/types.h>
   
7. #include<linux/kdev_t.h>
   
8. #include<linux/cdev.h>
   
9. #include<asm/uaccess.h>
   
10. #include<linux/slab.h>
    
11. #include<linux/mm.h>
    
12. 
    
13. #if 1
    
14. #define dprintk(fmt,args...) \
    
15.     printk("Dbg->%s_%d:"fmt,__FUNCTION__,__LINE__,##args)
    
16. #else
    
17. #define dprintk(fmt,args...)
    
18. #endif
    
19. 
    
20. #define eprintk(fmt,args...) \
    
21.     printk("Err->%s_%d:"fmt,__FUNCTION__,__LINE__,##args)
    
22. 
    
23. static int gMajor = 0 ;
    
24. static int gMinor = 0 ;
    
25. module_param(gMajor,int,0);
    
26. 
    
27. #define DEVICE "test"
    
28. 
    
29. struct cdev * my_cdev = NULL ;
    
30. 
    
31. #define KMALLOC_SIZE 1024*80
    
32. 
    
33. int test_open(struct inode *inode,struct file *filp)
    
34. {
    
35.     struct cdev * pdev = NULL ;
    
36.     int major = 0 ;
    
37.     filp->private_data = kmalloc(KMALLOC_SIZE,GFP_KERNEL) ;
    
38.     if(filp->private_data==NULL){
    
39.         printk("test_open error !!!\n");
    
40.         return -1 ;
    
41.     }
    
42.     if(inode->i_cdev)pdev= inode->i_cdev ;
    
43.     major = MAJOR(pdev->dev) ;
    
44.     dprintk("major = %d \n",major) ;
    
45.     return 0;
    
46. 
    
47. }
    
48. 
    
49. int test_release(struct inode *inode ,struct file *filp)
    
50. {
    
51.     if(filp->private_data)kfree(filp->private_data);
    
52.     dprintk("\n");
    
53.     return 0;
    
54. }
    
55. 
    
56. ssize_t test_read(struct file *filp,char __user *buffer,size_t count,loff_t *offp)
    
57. {
    
58.     int ret = -1 ;
    
59.     dprintk("the file position *offp = %lld,file pos =%lld\n",(long long)(*offp),(long long)filp->f_pos);
    
60.     if(count +*offp>KMALLOC_SIZE){
    
61.        count = KMALLOC_SIZE - *offp ;
    
62.     }
    
63.     ret =  copy_to_user(buffer,filp->private_data+(*offp),(unsigned long)count);
    
64.     if(ret != 0){
    
65.         eprintk("test_read error ret = %d!!!\n",ret);
    
66.         return -1 ;
    
67.     }
    
68. 
    
69.     *offp +=count ;
    
70.    dprintk("the file position *offp = %lld,file pos =%lld\n",(long long)(*offp),(long long)filp->f_pos);
    
71.    return count ;
    
72. }
    
73. 
    
74. ssize_t test_write(struct file *filp,const char __user *buffer,size_t count,loff_t *offp)
    
75. {
    
76.     int ret = -1 ;
    
77. 
    
78.     if(*offp+count>KMALLOC_SIZE){
    
79.         printk("the device space is limit\n");
    
80.         count = KMALLOC_SIZE-*offp ;
    
81.     }
    
82.     ret = copy_from_user((char *)filp->private_data+(*offp),buffer,count);
    
83.     if(ret != 0){
    
84.         eprintk("write error ret = %d!!!\n",ret);
    
85.         return ret ;
    
86.     }
    
87.     *offp +=count ;
    
88.     dprintk("the file position *offp = %lld,file pos =%lld\n",(long long)(*offp),(long long)filp->f_pos);
    
89.     return count ;
    
90. }
    
91. 
    
92. loff_t test_seek(struct file *filp,loff_t off,int where)
    
93. {
    
94. 
    
95. switch(where)
    
96. {
    
97.     case 0 :
    
98.      filp->f_pos = 0 ;
    
99.      filp->f_pos += off ;
    
100.     break ;
     
101.     case 1 :
     
102.      filp->f_pos += off ;
     
103.      break ;
     
104.     case 2 :
     
105.      filp->f_pos = 0 ;
     
106.      filp->f_pos += KMALLOC_SIZE  ;
     
107.     default :
     
108.         break ;
     
109.   }
     
110.    return filp->f_pos ;
     
111. }
     
112. 
     
113. int test_mmap(struct file *filp,struct vm_area_struct *vm)
     
114. {
     
115.     unsigned long phy_addr = __pa(filp->private_data);
     
116.     unsigned long pfn = (phy_addr>>PAGE_SHIFT) + vm->vm_pgoff [color=Red];//主要在于如果vm_pgoff不为0时则实现不了功能。[/color]    dprintk("pfn = %ld,phy_addr = %x pgoff = %d\n",pfn,phy_addr,vm->vm_pgoff);
     
117.     dprintk("vm->vm_start = 0x%x vm->vm_end = 0x%x size = %d vm->vm_pgoff = %d \n",vm->vm_start,vm->vm_end,\
     
118.              vm->vm_end - vm->vm_start,vm->vm_pgoff);
     
119. 
     
120.     if(remap_pfn_range(vm,vm->vm_start,pfn,vm->vm_end-vm->vm_start,vm->vm_page_prot))
     
121.         return -EAGAIN;
     
122.     vm->vm_flags |= VM_RESERVED ;
     
123.     vm->vm_page_prot = pgprot_noncached(vm->vm_page_prot);
     
124.     return 0;
     
125. }
     
126. 
     
127. struct file_operations  my_ops = {
     
128.     .owner   = THIS_MODULE ,
     
129.     .open    = test_open ,
     
130.     .release = test_release ,
     
131.     .mmap    = test_mmap ,
     
132.     .read    = test_read ,
     
133.     .write   = test_write ,
     
134.     .llseek  = test_seek ,
     
135. } ;
     
136. 
     
137. static int __init test_init(void)
     
138. {
     
139.     dev_t dev ;
     
140.     int ret = -1 ;
     
141.     dprintk("module init\n");
     
142.     if(gMajor!=0){
     
143.         dev = MKDEV(gMajor,gMinor) ;
     
144.         ret = register_chrdev_region(dev,1,DEVICE) ;
     
145.     }else{
     
146.        ret  = alloc_chrdev_region(&dev,0,1,DEVICE) ;
     
147.        gMajor = MAJOR(dev);
     
148.     }
     
149.     if(ret != 0){
     
150.         dprintk("register chrdev dev error \n");
     
151.         return ret ;
     
152.     }
     
153.     dprintk("major = %d \n",gMajor);
     
154. 
     
155.     my_cdev = cdev_alloc() ;
     
156.     my_cdev->ops = &my_ops ;
     
157.     my_cdev->owner = THIS_MODULE ;
     
158.     cdev_add(my_cdev,dev,1) ;
     
159.     return 0;
     
160. }
     
161. 
     
162. static void __exit test_exit(void)
     
163. {
     
164.    dprintk("module exit \n");
     
165.    cdev_del(my_cdev) ;
     
166.    unregister_chrdev_region(MKDEV(gMajor,gMinor),1);
     
167. }
     
168. 
     
169. module_init(test_init) ;
     
170. module_exit(test_exit) ;
     
171. MODULE_LICENSE("GPL");
     
172. MODULE_AUTHOR("BIN");

复制代码

---

欢迎光临 Chinaunix (http://bbs.chinaunix.net/)

Powered by Discuz! X3.2