一、用到的API与数据结构先看用户空间使用的API
- #include <sys/mman.h>
-
void *mmap(void *start, //映射的范围首地址,通常设NULL,让系统自动选地址,映射成功后返回该地址
- size_t length, //映射的范围的大小
- int prot, //映射区的保护属性 PROT_EXEC PROT_READ PROT_WRITE PROT_NONE
- int flags, //映射区的属性,注意MAP_SHARED、MAP_PRIVATE必选其一
- int fd, //文件描述符
- off_t offsize);//偏移量,后面讲
- 返回值:若映射成功则返回映射区的内存起始地址,否则返回MAP_FAILED(-1),错误原因存于errno 中。
- 另外注意: offsize参数是有限制的。。。(以下摘自man手册)
- EINVAL We don’t like start or length or offset.
- (E.g., they are too large, or not aligned on a PAGESIZE boundary.)
在字符设备驱动模块里,有一个stuct file_operations结构
其中的fop->mmap() 指向你自己的mmap钩子函数。
用户空间里对一个字符设备文件进行mmap()系统调用后,最终会调用驱动模块里的mmap钩子函数
在mmap钩子函数里,需要调用下面这个API
- int remap_pfn_range(struct vm_area_struct *vma, //这个结构很重要!!后面讲
-
unsigned long virt_addr, //要映射的范围的首地址
-
unsigned long pfn, //要映射的范围对应的物理内存的页帧号!!重要
-
unsigned long size, //要映射的范围的大小
-
pgprot_t prot); //PROTECT属性,mmap()中来的
内核维护VMA的链表和树形结构(即vm_area_struct),我们没事别建新的VMA,否则会打破这种组织结构。
用户空间每次调用mmap(),内核都会新建一个vm_area_struct数据结构,我们只关注几个重要的成员
- struct vm_area_struct{
-
unsigned long vm_start; //要映射的范围的首地址
-
unsigned long vm_end; //要映射的范围的尾地址
-
-
pgprot_t vm_page_prot; //来自mmap()的形参prot
- sturct file *vm_file; //字符设备文件所对应的file数据结构
-
unsigned long vm_pgoff; //来自mmap()的形参offsize,注意它是以PAGE为单位的,不是字节
-
unsigned long vm_flags; //来自mmap()的形参flags
-
}
在你的mmap钩子函数里,象下面这样就可以了
- int my_mmap(struct file *filp, struct vm_area_struct *vma){
-
//......省略,page很重要,其他的参数一般照下面就可以了
-
remap_pfn_range(vma, vma->vm_start, page,
- (vma->vm_end - vma->vm_start), vma->vm_page_prot);
-
//......省略
-
}
二、代码示例内核模块里分配内存,通过proc把此内存的EA地址、大小告诉用户空间。
用户空间通过proc获取内存相关信息后,调用mmap,往内存里写字符串。
内核模块代码:
- #include <linux/module.h>
-
#include <linux/types.h>
-
#include <linux/fs.h>
-
#include <asm/io.h>
-
#include <asm/system.h>
-
#include <linux/cdev.h>
-
#include <linux/proc_fs.h>
-
#include <linux/mm.h>
-
#define PROC_SHM_MAP_DIR "shm_dir"
-
#define PROC_SHM_MAP_INFO "shm_info"
-
#define PAGE_ORDER 0
-
#define PAGES_NUMBER 1
-
-
static int dbg_major = 215;
-
struct cdev dgb_dev;
-
struct proc_dir_entry *proc_shm_map_dir;
-
unsigned long kernel_memaddr = 0;
-
unsigned long kernel_memsize = 0;
-
-
int get_shm_proc_info(char *page, char **start, off_t off, int count)
-
{
-
return sprintf(page, "lx %lu\n", __pa(kernel_memaddr), kernel_memsize);
-
}
-
-
void create_shm_proc(void)
-
{
-
if(NULL == (proc_shm_map_dir = proc_mkdir(PROC_SHM_MAP_DIR, NULL)) ){
-
printk("proc create error!\n");
-
return ;
-
}
-
create_proc_info_entry(PROC_SHM_MAP_INFO, 0, proc_shm_map_dir, get_shm_proc_info);
-
}
-
-
void destroy_shm_proc(void)
-
{
-
remove_proc_entry(PROC_SHM_MAP_INFO, proc_shm_map_dir);
-
remove_proc_entry(PROC_SHM_MAP_DIR, NULL);
-
}
-
-
int shm_mmap(struct file *filp, struct vm_area_struct *vma)
-
{
-
unsigned long page;
-
page = virt_to_phys((void *)kernel_memaddr) >> PAGE_SHIFT;
-
-
if( remap_pfn_range(vma, vma->vm_start, page, (vma->vm_end - vma->vm_start),
- vma->vm_page_prot) )
-
return -1;
-
vma->vm_flags |= VM_RESERVED;
-
printk("remap_pfn_rang page:[%lu] ok.\n", page);
-
return 0;
-
}
-
-
int create_shm_mem(void)
-
{
-
if( NULL == (kernel_memaddr =__get_free_pages(GFP_KERNEL, PAGE_ORDER) )) {
-
printk("alloc kernel memory failed!\n");
-
return -1;
-
}
-
SetPageReserved(virt_to_page(kernel_memaddr)); // important !! only 1 page
-
kernel_memsize = PAGES_NUMBER * PAGE_SIZE;
-
printk("The kernel mem addr=lx, size=%lu\n",__pa(kernel_memaddr), kernel_memsize);
-
return 0;
-
}
-
void destroy_shm_mem(void)
-
{
-
printk("The string written by user is: %s\n", (unsigned char *)kernel_memaddr);
-
ClearPageReserved(virt_to_page(kernel_memaddr));// important !!
-
free_pages(kernel_memaddr, PAGE_ORDER);
-
return;
-
}
-
-
static const struct file_operations dbg_fops ={
-
.owner = THIS_MODULE,
-
.mmap = shm_mmap,
-
};
-
-
static void dbg_exit(void)
-
{
-
cdev_del(&dgb_dev);
-
unregister_chrdev_region(MKDEV(dbg_major, 0), 1);
-
destroy_shm_proc();
-
destroy_shm_mem();
-
}
-
-
int dbg_init(void)
-
{
-
int result;
-
dev_t devno ;
-
struct cdev *p_cdev = &dgb_dev;
-
-
if (dbg_major){
-
devno =MKDEV(dbg_major,0);
-
result = register_chrdev_region(devno,1, "leon");
-
}
-
else{
-
result=alloc_chrdev_region(&devno, 0, 1,"leon");
-
dbg_major = MAJOR(devno);
-
}
-
-
if (result < 0)
-
return result;
-
printk("the major device No. is %d\n", dbg_major );
-
-
cdev_init(p_cdev,&dbg_fops);
-
p_cdev->owner = THIS_MODULE;
-
result = cdev_add(p_cdev,devno,1);
-
-
if(result){
-
printk(KERN_NOTICE "Error %d while adding dbg",result);
-
return result;
-
}
-
-
create_shm_mem();
-
create_shm_proc();
-
return 0;
-
}
-
-
MODULE_AUTHOR("leonwang202");
-
MODULE_LICENSE("Dual BSD/GPL");
-
module_init(dbg_init);
-
module_exit(dbg_exit);
用户空间代码:
- #include <stdio.h>
-
#include <stdlib.h>
-
#include <unistd.h>
-
#include <string.h>
-
#include <fcntl.h>
-
#include <sys/stat.h>
-
#include <sys/types.h>
-
#include <sys/mman.h>
-
#include <errno.h>
-
-
int main(int argc, char* argv[])
-
{
-
if(argc != 2) {
-
printf("Usage: %s string\n", argv[0]);
-
return 0;
-
}
-
unsigned long phymem_addr, phymem_size;
-
char *map_addr;
-
char s[256];
-
int fd;
-
-
if( (fd = open("/proc/shm_dir/shm_info", O_RDONLY)) < 0) {
-
printf("cannot open file /proc/shm_dir/shm_info\n");
-
return 0;
-
}
-
-
read(fd, s, sizeof(s));
-
if(2 != sscanf(s, "lx %lu", &phymem_addr, &phymem_size)){
-
printf("data format from /proc/shm_dir/shm_info error!\n");
-
close(fd);
-
return -1;
-
};
-
close(fd);
-
printf("phymem_addr=%lx, phymem_size=%lu\n", phymem_addr, phymem_size);
-
-
if( (fd = open("/dev/enetdbg", O_RDWR|O_NONBLOCK)) < 0){
-
printf("open /dev/enetdbg error!\n");
-
return -1;
-
}
-
-
map_addr = mmap(NULL,
-
phymem_size,
-
PROT_READ|PROT_WRITE,
-
MAP_SHARED,
-
fd,
-
0); // ignored, because we don't use "vm->pgoff" in driver.
-
-
if( MAP_FAILED == map_addr){
-
printf("mmap() error:[%d]\n", errno);
-
return -1;
-
}
-
-
strcpy(map_addr, argv[1]);
-
munmap(map_addr, phymem_size);
-
-
close(fd);
-
return 0;
-
}
注意:我们在shm_mmap里没使用vm->pgoff,所以mmap()的形参offsize可以无视。三、使用/dev/mem想偷懒的,可以使/dev/mem,就不用费劲写内核模块里的mmap钩子函数了
(此用法在帖子中有写)
内核代码不用改,图干净的话只要把mmap钩子函数相关的东东全删掉就ok了
用户空间代码得改:
- #include <stdio.h>
-
#include <stdlib.h>
-
#include <unistd.h>
-
#include <string.h>
-
#include <fcntl.h>
-
#include <sys/stat.h>
-
#include <sys/types.h>
-
#include <sys/mman.h>
-
#include <errno.h>
-
-
int main(int argc, char* argv[])
-
{
-
if(argc != 2) {
-
printf("Usage: %s string\n", argv[0]);
-
return 0;
-
}
-
unsigned long phymem_addr, phymem_size;
-
char *map_addr;
-
char s[256];
-
int fd;
-
-
if( (fd = open("/proc/shm_dir/shm_info", O_RDONLY)) < 0) {
-
printf("cannot open file /proc/shm_dir/shm_info\n");
-
return 0;
-
}
-
read(fd, s, sizeof(s));
-
if(2 != sscanf(s, "lx %lu", &phymem_addr, &phymem_size)){
-
printf("data format from /proc/shm_dir/shm_info error!\n");
-
close(fd);
-
return -1;
-
};
-
close(fd);
-
printf("phymem_addr=%lx, phymem_size=%lu\n", phymem_addr, phymem_size);
-
-
if( (fd = open("/dev/mem", O_RDWR|O_NONBLOCK)) < 0){
-
printf("open /dev/mem error!\n");
-
exit(0);
-
}
-
map_addr = mmap(NULL,
-
phymem_size,
-
PROT_READ|PROT_WRITE,
-
MAP_SHARED,
-
fd,
-
phymem_addr);
-
-
strcpy(map_addr, argv[1]);
-
munmap(map_addr, phymem_size);
-
close(fd);
-
return 0;
-
}
注意:
1.你的linux环境下没有/dev/mem的话,敲命令 mknod /dev/mem c 1 1 原因后面讲
2.这次mmap()形参offsize不能无视,因为创建/dev/mem的内核模块的mmap钩子函数里用到了vm->pgoff看到底是哪个模块创建了/dev/mem
- start_kernel --> kernel_init --> do_basic_setup --> do_initcalls --> chr_dev_init
文件 linux_2_6_24/drivers/char/mem.c 中 chr_dev_init() 函数
- static int __init chr_dev_init(void)
-
{
-
if (register_chrdev(MEM_MAJOR,"mem",&memory_fops)) //cat /proc/devices 时显示 1 mem
-
printk("unable to get major %d for memory devs\n", MEM_MAJOR);
-
-
for (i = 0; i < ARRAY_SIZE(devlist); i )
-
device_create(mem_class, NULL, //据数组新建N多设备,主设备号为1,从设备号来自数组
-
MKDEV(MEM_MAJOR, devlist[i].minor),devlist[i].name);
-
}
-
-
static const struct {
-
unsigned int minor;
-
char *name;
-
umode_t mode;
-
const struct file_operations *fops;
-
} devlist[] = { /* list of minor devices */ //我擦,major为1的字符设备这么多....
-
{1, "mem", S_IRUSR | S_IWUSR | S_IRGRP, &mem_fops}, //mknod /dev/mem c 1 1 原因知道了吧
-
{2, "kmem", S_IRUSR | S_IWUSR | S_IRGRP, &kmem_fops},
-
{3, "null", S_IRUGO | S_IWUGO, &null_fops},
-
#ifdef CONFIG_DEVPORT
-
{4, "port", S_IRUSR | S_IWUSR | S_IRGRP, &port_fops},
-
#endif
-
{5, "zero", S_IRUGO | S_IWUGO, &zero_fops},
-
{7, "full", S_IRUGO | S_IWUGO, &full_fops},
-
{8, "random", S_IRUGO | S_IWUSR, &random_fops},
-
{9, "urandom", S_IRUGO | S_IWUSR, &urandom_fops},
-
{11,"kmsg", S_IRUGO | S_IWUSR, &kmsg_fops},
-
#ifdef CONFIG_CRASH_DUMP
-
{12,"oldmem", S_IRUSR | S_IWUSR | S_IRGRP, &oldmem_fops},
-
#endif
-
};
---------------------------------- 华丽的分割线 -------------------------------------------
若共享小块连续内存,上面例子用get_free_pages可以分配多达几M的连续空间(MAX_ORDER目前是11)。
若共享大块连续内存,就得靠uboot帮忙了,给linux kernel传参数的时候,用mem=大小
《ldd3》中的分配内存那章有专门一节讲解,通过API
- void *alloc_bootmem(unsigned long size);
-
void free_bootmem(unsigned long addr, unsigned long size);
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