mmap的使用（应用程序使用与模块调用的分别实现）
时间：2009-08-01 来源：red_eyed_hare
功能描述：
mmap将一个文件或者其它对象映射进内存。文件被映射到多个页上，如果文件的大小不是所有页的大小之和，最后一个页不被使用的空间将会清零。munmap执行相反的操作，删除特定地址区域的对象映射。
基于文件的映射，在mmap和munmap执行过程的任何时刻，被映射文件的st_atime可能被更新。如果st_atime字段在前述的情况下没有得到更新，首次对映射区的第一个页索引时会更新该字段的值。用PROT_WRITE 和 MAP_SHARED标志建立起来的文件映射，其st_ctime 和 st_mtime在对映射区写入之后，但在msync()通过MS_SYNC 和 MS_ASYNC两个标志调用之前会被更新。
用法：
#include <sys/mman.h>
void *mmap(void *start, size_t length, int prot, int flags,
int fd, off_t offset);
int munmap(void *start, size_t length);
参数：
start：映射区的开始地址。
length：映射区的长度。
prot：期望的内存保护标志，不能与文件的打开模式冲突。是以下的某个值，可以通过or运算合理地组合在一起
PROT_EXEC //页内容可以被执行
PROT_READ //页内容可以被读取
PROT_WRITE //页可以被写入
PROT_NONE //页不可访问
flags：指定映射对象的类型，映射选项和映射页是否可以共享。它的值可以是一个或者多个以下位的组合体
MAP_FIXED //使用指定的映射起始地址，如果由start和len参数指定的内存区重叠于现存的映射空间，重叠部分将会被丢弃。如果指定的起始地址不可用，操作将会失败。并且起始地址必须落在页的边界上。
MAP_SHARED //与其它所有映射这个对象的进程共享映射空间。对共享区的写入，相当于输出到文件。直到msync()或者munmap()被调用，文件实际上不会被更新。
MAP_PRIVATE //建立一个写入时拷贝的私有映射。内存区域的写入不会影响到原文件。这个标志和以上标志是互斥的，只能使用其中一个。
MAP_DENYWRITE //这个标志被忽略。
MAP_EXECUTABLE //同上
MAP_NORESERVE //不要为这个映射保留交换空间。当交换空间被保留，对映射区修改的可能会得到保证。当交换空间不被保留，同时内存不足，对映射区的修改会引起段违例信号。
MAP_LOCKED //锁定映射区的页面，从而防止页面被交换出内存。
MAP_GROWSDOWN //用于堆栈，告诉内核VM系统，映射区可以向下扩展。
MAP_ANONYMOUS //匿名映射，映射区不与任何文件关联。
MAP_ANON //MAP_ANONYMOUS的别称，不再被使用。
MAP_FILE //兼容标志，被忽略。
MAP_32BIT //将映射区放在进程地址空间的低2GB，MAP_FIXED指定时会被忽略。当前这个标志只在x86-64平台上得到支持。
MAP_POPULATE //为文件映射通过预读的方式准备好页表。随后对映射区的访问不会被页违例阻塞。
MAP_NONBLOCK //仅和MAP_POPULATE一起使用时才有意义。不执行预读，只为已存在于内存中的页面建立页表入口。
fd：有效的文件描述词。如果MAP_ANONYMOUS被设定，为了兼容问题，其值应为-1。
offset：被映射对象内容的起点。
返回说明：
成功执行时，mmap()返回被映射区的指针，munmap()返回0。失败时，mmap()返回MAP_FAILED[其值为(void *)-1]，munmap返回-1。errno被设为以下的某个值
EACCES：访问出错
EAGAIN：文件已被锁定，或者太多的内存已被锁定
EBADF：fd不是有效的文件描述词
EINVAL：一个或者多个参数无效
ENFILE：已达到系统对打开文件的限制
ENODEV：指定文件所在的文件系统不支持内存映射
ENOMEM：内存不足，或者进程已超出最大内存映射数量
EPERM：权能不足，操作不允许
ETXTBSY：已写的方式打开文件，同时指定MAP_DENYWRITE标志
SIGSEGV：试着向只读区写入
SIGBUS：试着访问不属于进程的内存区
以下介绍mmap实现程序，程序都在Linux red hat 9.0下顺利运行：
#ifndef __KERNEL__
# define __KERNEL__
#endif
#ifndef MODULE
# define MODULE
#endif #include <linux/config.h>
#include <linux/module.h> #include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <asm/page.h>
MODULE_LICENSE("GPL");
#include "sysdep.h" #ifdef LINUX_20
# error "This module can't run with Linux-2.0"
#endif static int simple_major = 0;
MODULE_PARM(simple_major, "i");
MODULE_AUTHOR("baoqunmin"); int simple_open (struct inode *inode, struct file *filp);
int simple_release(struct inode *inode, struct file *filp);
int simple_remap_mmap(struct file *filp, struct vm_area_struct *vma);
int simple_nopage_mmap(struct file *filp, struct vm_area_struct *vma); /* Device 0 uses remap_page_range */
struct file_operations simple_remap_ops = {
open: simple_open,
release: simple_release,
mmap: simple_remap_mmap,
}; /* Device 1 uses nopage */
struct file_operations simple_nopage_ops = {
open: simple_open,
release: simple_release,
mmap: simple_nopage_mmap,
}; #define MAX_SIMPLE_DEV 2 struct file_operations *simple_fops[MAX_SIMPLE_DEV] = {
&simple_remap_ops,
&simple_nopage_ops,
}; int simple_open (struct inode *inode, struct file *filp)
{
unsigned int dev = MINOR(inode->i_rdev); if (dev >= MAX_SIMPLE_DEV)
return -ENODEV;
filp->f_op = simple_fops[dev];
MOD_INC_USE_COUNT;
printk("simple is open\n");
return 0;
} int simple_release(struct inode *inode, struct file *filp)
{
MOD_DEC_USE_COUNT;
printk("simple is close\n");
return 0;
} void simple_vma_open(struct vm_area_struct *vma)
{ MOD_INC_USE_COUNT; } void simple_vma_close(struct vm_area_struct *vma)
{ MOD_DEC_USE_COUNT; } static struct vm_operations_struct simple_remap_vm_ops = {
open: simple_vma_open,
close: simple_vma_close,
}; int simple_remap_mmap(struct file *filp, struct vm_area_struct *vma)
{
unsigned long offset = VMA_OFFSET(vma); if (offset >= __pa(high_memory) || (filp->f_flags & O_SYNC))
vma->vm_flags |= VM_IO;
vma->vm_flags |= VM_RESERVED; if (remap_page_range(vma,vma->vm_start, offset, vma->vm_end-vma->vm_start,vma->vm_page_prot)
)
return -EAGAIN; vma->vm_ops = &simple_remap_vm_ops;
simple_vma_open(vma);
printk("good morning baoqunmin\n");
return 0;
}
struct page *simple_vma_nopage(struct vm_area_struct *vma,
unsigned long address, int write_access)
{
struct page *pageptr;
unsigned long physaddr = address - vma->vm_start + VMA_OFFSET(vma);
pageptr = virt_to_page(__va(physaddr));
get_page(pageptr);
printk("good morning bao\n");
return pageptr;
}
#ifdef LINUX_22 /* wrapper for 2.2, which had a different nopage retval */
unsigned long simple_vma_nopage_22(struct vm_area_struct * area,
unsigned long address, int write_access)
{
return (unsigned long) simple_vma_nopage(area, address, write_access);
}
#define simple_vma_nopage simple_vma_nopage_22
#endif /* LINUX_22 */
static struct vm_operations_struct simple_nopage_vm_ops = {
open: simple_vma_open,
close: simple_vma_close,
nopage: simple_vma_nopage,
};
int simple_nopage_mmap(struct file *filp, struct vm_area_struct *vma)
{
unsigned long offset = VMA_OFFSET(vma); if (offset >= __pa(high_memory) || (filp->f_flags & O_SYNC))
vma->vm_flags |= VM_IO;
vma->vm_flags |= VM_RESERVED; vma->vm_ops = &simple_nopage_vm_ops;
simple_vma_open(vma);
return 0;
}
static int simple_init(void)
{
int result; SET_MODULE_OWNER(&simple_remap_ops);
SET_MODULE_OWNER(&simple_nopage_ops); result = register_chrdev(simple_major, "simple", &simple_remap_ops);
if (result < 0)
{
printk(KERN_WARNING "simple: unable to get major %d\n", simple_major);
return result;
}
if (simple_major == 0)
simple_major = result;
printk("simple ok!\n");
return 0;
}
static void simple_cleanup(void)
{
unregister_chrdev(simple_major, "simple");
printk("simple close\n");
}
module_init(simple_init);
module_exit(simple_cleanup); 上面给出"sysdep.h"头文件，此程序在Linux设备驱动编程一书中给出，读者可以轻松找到，由于代码多，这就不给出了。 Makefile文件如下所示： CC=gcc
MODCFLAGS := -Wall -DMODULE -D__KERNEL__ -DLINUX -I/usr/src/linux-2.4.20-8/include
mmap.o :mmap.c
$(CC) $(MODCFLAGS) -c mmap.c
echo insmod mmap.o to turn it on
echo rmmod mmap to turn it off
echo 加载文件如下（bao_load.sh）： #!/bin/bash
#bao.sh
make
/sbin/insmod mmap.o
module="simple"
device="simple"
cat /proc/devices
#get the major of the module
major=`cat /proc/devices | awk "\\$2==\"$module\" {print \\$1}"`
mknod /dev/${device} c $major 0
echo "finish" 卸载文件如下（bao_unload.sh）： #!/bin/bash
#bao.sh
rm -i /dev/simple
/sbin/rmmod mmap
cat /proc/devices
echo "finish" 用户测试程序如下(tmmap.c)： #include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h> int main(void)
{
int fd;
int i=0;
unsigned int *vadr;
unsigned int *kadr; int len = getpagesize(); if ((fd=open("/dev/simple", O_RDWR|O_SYNC))<0)
{
perror("open");
exit(-1);
}
vadr=(int*)mmap(NULL, len , PROT_READ|PROT_WRITE, MAP_SHARED , fd , 0);
if (vadr == MAP_FAILED)
{
perror("mmap");
exit(-1);
}
for(i=0;i<(len/4);i++)
{
(*(vadr+i))=i;
}
printf("initialize over\n");
munmap(vadr,len);
kadr=(int*)mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (kadr == MAP_FAILED)
{
perror("mmap");
exit(-1);
}
for(i=0;i<(len/4);i++)
{
printf("the number is %d\n",(*(vadr+i)));
}
munmap(kadr,len);
close(fd);
return(0);
} 应用程序测试，运行步骤如下： 1.在终端直接运行 sh bao_load.sh或./bao_load.sh加载设备 2.gcc -o tmmap tmmap.c 3../tmmap 4.dmesg 查看内核打印情况 5.sh bao_unload.sh 卸载设备 内核模块调用程序如下（bao.c）： #include <linux/module.h>
#define __KERNEL_SYSCALLS__
#ifdef MODVERSIONS
#include <linux/modversion.h>
#endif
#include <linux/config.h>
#include <linux/smp_lock.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/stat.h>
#include <asm/mman.h>
#include <linux/file.h>
#include <linux/unistd.h>
#include <asm/io.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <asm/fcntl.h>
#include <asm/uaccess.h>
#include <asm/errno.h>
#include <linux/syscall.h>
#ifndef MAP_FAILED
#define MAP_FAILED ((void *)-1)
#endif
static inline _syscall6(void*,mmap2,void*,addr,size_t,len,int,prot,int,flags,int,fd,off_t,offset);
static inline _syscall2(int, munmap, int*, a, int, b);
MODULE_LICENSE("GPL"); #define BEGIN_KMEM { mm_segment_t old_fs = get_fs(); set_fs(get_ds());
#define END_KMEM set_fs(old_fs); }
int errno; int init_module(void){
int fd;
size_t len =100;
int i=0;
unsigned int *vadr;
unsigned int *kadr;
printk("<1>Hello,world\n");
BEGIN_KMEM;
if ((fd=open("/dev/simple", O_RDWR|O_SYNC,0))<0)
{
printk("open failed\n");
return 1;
}
vadr=(int*)mmap2(NULL,len,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
if (vadr == MAP_FAILED)
{
printk("mmap\n");
return 1;
}
for(i=0;i<(len/4);i++)
{
(*(vadr+i))=i;
}
printk("initialize over\n");
munmap(vadr,len);
kadr=(int*)mmap2(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (kadr == MAP_FAILED)
{
printk("mmap\n");
return 1;
}
for(i=0;i<(len/4);i++)
{
printk("the number is %d\n",(*(vadr+i)));
}
munmap(kadr,len);
close(fd);
END_KMEM;
return 0;
}
void cleanup_module(void){
printk("<1>Goodbye cruel word\n");
} makefile文件如下： CC=gcc
MODCFLAGS := -Wall -DMODULE -D__KERNEL__ -DLINUX -I/usr/src/linux-2.4.20-8/include
bao.o :bao.c
$(CC) $(MODCFLAGS) -c bao.c
echo insmod bao.o to turn it on
echo rmmod bao to turn it off
echo 模块调用测试步骤如下： 1.在终端直接运行 sh bao_load.sh或./bao_load.sh加载设备 2.进入bao.c文件目录下 make 3./sbin/insmod bao.o加载模块 4.dmesg 查看内核打印情况 5./sbin/rmmod bao卸载模块 5.sh bao_unload.sh 卸载设备 以上完成了用户程序调用mmap和内核模块调用mmap，供大家参考！
# define __KERNEL__
#endif
#ifndef MODULE
# define MODULE
#endif #include <linux/config.h>
#include <linux/module.h> #include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <asm/page.h>
MODULE_LICENSE("GPL");
#include "sysdep.h" #ifdef LINUX_20
# error "This module can't run with Linux-2.0"
#endif static int simple_major = 0;
MODULE_PARM(simple_major, "i");
MODULE_AUTHOR("baoqunmin"); int simple_open (struct inode *inode, struct file *filp);
int simple_release(struct inode *inode, struct file *filp);
int simple_remap_mmap(struct file *filp, struct vm_area_struct *vma);
int simple_nopage_mmap(struct file *filp, struct vm_area_struct *vma); /* Device 0 uses remap_page_range */
struct file_operations simple_remap_ops = {
open: simple_open,
release: simple_release,
mmap: simple_remap_mmap,
}; /* Device 1 uses nopage */
struct file_operations simple_nopage_ops = {
open: simple_open,
release: simple_release,
mmap: simple_nopage_mmap,
}; #define MAX_SIMPLE_DEV 2 struct file_operations *simple_fops[MAX_SIMPLE_DEV] = {
&simple_remap_ops,
&simple_nopage_ops,
}; int simple_open (struct inode *inode, struct file *filp)
{
unsigned int dev = MINOR(inode->i_rdev); if (dev >= MAX_SIMPLE_DEV)
return -ENODEV;
filp->f_op = simple_fops[dev];
MOD_INC_USE_COUNT;
printk("simple is open\n");
return 0;
} int simple_release(struct inode *inode, struct file *filp)
{
MOD_DEC_USE_COUNT;
printk("simple is close\n");
return 0;
} void simple_vma_open(struct vm_area_struct *vma)
{ MOD_INC_USE_COUNT; } void simple_vma_close(struct vm_area_struct *vma)
{ MOD_DEC_USE_COUNT; } static struct vm_operations_struct simple_remap_vm_ops = {
open: simple_vma_open,
close: simple_vma_close,
}; int simple_remap_mmap(struct file *filp, struct vm_area_struct *vma)
{
unsigned long offset = VMA_OFFSET(vma); if (offset >= __pa(high_memory) || (filp->f_flags & O_SYNC))
vma->vm_flags |= VM_IO;
vma->vm_flags |= VM_RESERVED; if (remap_page_range(vma,vma->vm_start, offset, vma->vm_end-vma->vm_start,vma->vm_page_prot)
)
return -EAGAIN; vma->vm_ops = &simple_remap_vm_ops;
simple_vma_open(vma);
printk("good morning baoqunmin\n");
return 0;
}
struct page *simple_vma_nopage(struct vm_area_struct *vma,
unsigned long address, int write_access)
{
struct page *pageptr;
unsigned long physaddr = address - vma->vm_start + VMA_OFFSET(vma);
pageptr = virt_to_page(__va(physaddr));
get_page(pageptr);
printk("good morning bao\n");
return pageptr;
}
#ifdef LINUX_22 /* wrapper for 2.2, which had a different nopage retval */
unsigned long simple_vma_nopage_22(struct vm_area_struct * area,
unsigned long address, int write_access)
{
return (unsigned long) simple_vma_nopage(area, address, write_access);
}
#define simple_vma_nopage simple_vma_nopage_22
#endif /* LINUX_22 */
static struct vm_operations_struct simple_nopage_vm_ops = {
open: simple_vma_open,
close: simple_vma_close,
nopage: simple_vma_nopage,
};
int simple_nopage_mmap(struct file *filp, struct vm_area_struct *vma)
{
unsigned long offset = VMA_OFFSET(vma); if (offset >= __pa(high_memory) || (filp->f_flags & O_SYNC))
vma->vm_flags |= VM_IO;
vma->vm_flags |= VM_RESERVED; vma->vm_ops = &simple_nopage_vm_ops;
simple_vma_open(vma);
return 0;
}
static int simple_init(void)
{
int result; SET_MODULE_OWNER(&simple_remap_ops);
SET_MODULE_OWNER(&simple_nopage_ops); result = register_chrdev(simple_major, "simple", &simple_remap_ops);
if (result < 0)
{
printk(KERN_WARNING "simple: unable to get major %d\n", simple_major);
return result;
}
if (simple_major == 0)
simple_major = result;
printk("simple ok!\n");
return 0;
}
static void simple_cleanup(void)
{
unregister_chrdev(simple_major, "simple");
printk("simple close\n");
}
module_init(simple_init);
module_exit(simple_cleanup); 上面给出"sysdep.h"头文件，此程序在Linux设备驱动编程一书中给出，读者可以轻松找到，由于代码多，这就不给出了。 Makefile文件如下所示： CC=gcc
MODCFLAGS := -Wall -DMODULE -D__KERNEL__ -DLINUX -I/usr/src/linux-2.4.20-8/include
mmap.o :mmap.c
$(CC) $(MODCFLAGS) -c mmap.c
echo insmod mmap.o to turn it on
echo rmmod mmap to turn it off
echo 加载文件如下（bao_load.sh）： #!/bin/bash
#bao.sh
make
/sbin/insmod mmap.o
module="simple"
device="simple"
cat /proc/devices
#get the major of the module
major=`cat /proc/devices | awk "\\$2==\"$module\" {print \\$1}"`
mknod /dev/${device} c $major 0
echo "finish" 卸载文件如下（bao_unload.sh）： #!/bin/bash
#bao.sh
rm -i /dev/simple
/sbin/rmmod mmap
cat /proc/devices
echo "finish" 用户测试程序如下(tmmap.c)： #include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h> int main(void)
{
int fd;
int i=0;
unsigned int *vadr;
unsigned int *kadr; int len = getpagesize(); if ((fd=open("/dev/simple", O_RDWR|O_SYNC))<0)
{
perror("open");
exit(-1);
}
vadr=(int*)mmap(NULL, len , PROT_READ|PROT_WRITE, MAP_SHARED , fd , 0);
if (vadr == MAP_FAILED)
{
perror("mmap");
exit(-1);
}
for(i=0;i<(len/4);i++)
{
(*(vadr+i))=i;
}
printf("initialize over\n");
munmap(vadr,len);
kadr=(int*)mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (kadr == MAP_FAILED)
{
perror("mmap");
exit(-1);
}
for(i=0;i<(len/4);i++)
{
printf("the number is %d\n",(*(vadr+i)));
}
munmap(kadr,len);
close(fd);
return(0);
} 应用程序测试，运行步骤如下： 1.在终端直接运行 sh bao_load.sh或./bao_load.sh加载设备 2.gcc -o tmmap tmmap.c 3../tmmap 4.dmesg 查看内核打印情况 5.sh bao_unload.sh 卸载设备 内核模块调用程序如下（bao.c）： #include <linux/module.h>
#define __KERNEL_SYSCALLS__
#ifdef MODVERSIONS
#include <linux/modversion.h>
#endif
#include <linux/config.h>
#include <linux/smp_lock.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/stat.h>
#include <asm/mman.h>
#include <linux/file.h>
#include <linux/unistd.h>
#include <asm/io.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <asm/fcntl.h>
#include <asm/uaccess.h>
#include <asm/errno.h>
#include <linux/syscall.h>
#ifndef MAP_FAILED
#define MAP_FAILED ((void *)-1)
#endif
static inline _syscall6(void*,mmap2,void*,addr,size_t,len,int,prot,int,flags,int,fd,off_t,offset);
static inline _syscall2(int, munmap, int*, a, int, b);
MODULE_LICENSE("GPL"); #define BEGIN_KMEM { mm_segment_t old_fs = get_fs(); set_fs(get_ds());
#define END_KMEM set_fs(old_fs); }
int errno; int init_module(void){
int fd;
size_t len =100;
int i=0;
unsigned int *vadr;
unsigned int *kadr;
printk("<1>Hello,world\n");
BEGIN_KMEM;
if ((fd=open("/dev/simple", O_RDWR|O_SYNC,0))<0)
{
printk("open failed\n");
return 1;
}
vadr=(int*)mmap2(NULL,len,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
if (vadr == MAP_FAILED)
{
printk("mmap\n");
return 1;
}
for(i=0;i<(len/4);i++)
{
(*(vadr+i))=i;
}
printk("initialize over\n");
munmap(vadr,len);
kadr=(int*)mmap2(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (kadr == MAP_FAILED)
{
printk("mmap\n");
return 1;
}
for(i=0;i<(len/4);i++)
{
printk("the number is %d\n",(*(vadr+i)));
}
munmap(kadr,len);
close(fd);
END_KMEM;
return 0;
}
void cleanup_module(void){
printk("<1>Goodbye cruel word\n");
} makefile文件如下： CC=gcc
MODCFLAGS := -Wall -DMODULE -D__KERNEL__ -DLINUX -I/usr/src/linux-2.4.20-8/include
bao.o :bao.c
$(CC) $(MODCFLAGS) -c bao.c
echo insmod bao.o to turn it on
echo rmmod bao to turn it off
echo 模块调用测试步骤如下： 1.在终端直接运行 sh bao_load.sh或./bao_load.sh加载设备 2.进入bao.c文件目录下 make 3./sbin/insmod bao.o加载模块 4.dmesg 查看内核打印情况 5./sbin/rmmod bao卸载模块 5.sh bao_unload.sh 卸载设备 以上完成了用户程序调用mmap和内核模块调用mmap，供大家参考！
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