linux mmap

最新推荐文章于 2024-09-25 13:58:27 发布

转载最新推荐文章于 2024-09-25 13:58:27 发布 · 357 阅读

本文介绍了内存映射的基本概念，详细解释了如何通过mmap函数在用户空间和内核空间之间进行高效的数据传输，并展示了具体的驱动程序及应用程序示例。

一、概述

内存映射，简而言之就是将用户空间的一段内存区域映射到内核空间，映射成功后，用户对这段内存区域的修改可以直接反映到内核空间，同样，内核空间对这段区域的修改也直接反映用户空间。那么对于内核空间<---->用户空间两者之间需要大量数据传输等操作的话效率是非常高的。

以下是一个把普遍文件映射到用户空间的内存区域的示意图。

图一：

二、基本函数

mmap函数是unix/linux下的系统调用，详细内容可参考《Unix Netword programming》卷二12.2节。

mmap系统调用并不是完全为了用于共享内存而设计的。它本身提供了不同于一般对普通文件的访问方式，进程可以像读写内存一样对普通文件的操作。而Posix或系统V的共享内存IPC则纯粹用于共享目的，当然mmap()实现共享内存也是其主要应用之一。

mmap系统调用使得进程之间通过映射同一个普通文件实现共享内存。普通文件被映射到进程地址空间后，进程可以像访问普通内存一样对文件进行访问，不必再调用read()，write（）等操作。mmap并不分配空间, 只是将文件映射到调用进程的地址空间里（但是会占掉你的 virutal memory）, 然后你就可以用memcpy等操作写文件, 而不用write()了.写完后，内存中的内容并不会立即更新到文件中，而是有一段时间的延迟，你可以调用msync()来显式同步一下, 这样你所写的内容就能立即保存到文件里了.这点应该和驱动相关。不过通过mmap来写文件这种方式没办法增加文件的长度, 因为要映射的长度在调用mmap()的时候就决定了.如果想取消内存映射，可以调用munmap()来取消内存映射

void * mmap(void *start, size_t length, int prot , int flags, int fd, off_t offset)

mmap用于把文件映射到内存空间中，简单说mmap就是把一个文件的内容在内存里面做一个映像。映射成功后，用户对这段内存区域的修改可以直接反映到内核空间，同样，内核空间对这段区域的修改也直接反映用户空间。那么对于内核空间<---->用户空间两者之间需要大量数据传输等操作的话效率是非常高的。

start：要映射到的内存区域的起始地址，通常都是用NULL（NULL即为0）。NULL表示由内核来指定该内存地址

length：要映射的内存区域的大小

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 ：对映射区域的写入数据会复制回文件内, 而且允许其他映射该文件的进程共享。

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：文件描述符（由open函数返回）

offset：表示被映射对象（即文件）从那里开始对映，通常都是用0。该值应该为大小为PAGE_SIZE的整数倍

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

int munmap(void *start, size_t length)

start：要取消映射的内存区域的起始地址

length：要取消映射的内存区域的大小。

返回说明

成功执行时munmap()返回0。失败时munmap返回-1.

int msync(const void *start, size_t length, int flags);

对映射内存的内容的更改并不会立即更新到文件中，而是有一段时间的延迟，你可以调用msync()来显式同步一下, 这样你内存的更新就能立即保存到文件里

start：要进行同步的映射的内存区域的起始地址。

length：要同步的内存区域的大小

flag:flags可以为以下三个值之一：

MS_ASYNC : 请Kernel快将资料写入。

MS_SYNC : 在msync结束返回前，将资料写入。

MS_INVALIDATE : 让核心自行决定是否写入，仅在特殊状况下使用

三、用户空间和驱动程序的内存映射

3.1、基本过程

首先，驱动程序先分配好一段内存，接着用户进程通过库函数mmap()来告诉内核要将多大的内存映射到内核空间，内核经过一系列函数调用后调用对应的驱动程序的file_operation中指定的mmap函数，在该函数中调用remap_pfn_range()来建立映射关系。

3.2、映射的实现

首先在驱动程序分配一页大小的内存，然后用户进程通过mmap()将用户空间中大小也为一页的内存映射到内核空间这页内存上。映射完成后，驱动程序往这段内存写10个字节数据，用户进程将这些数据显示出来。

驱动程序：

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0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/slab.h></span></div><div><span class="lit" style="color: rgb(0, 102, 102);">12</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/errno.h></span></div><div><span class="lit" style="color: rgb(0, 102, 102);">13</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/ioctl.h></span></div><div><span class="lit" style="color: rgb(0, 102, 102);">14</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/cdev.h></span></div><div><span class="lit" style="color: rgb(0, 102, 102);">15</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/string.h></span></div><div><span class="lit" style="color: rgb(0, 102, 102);">16</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/list.h></span></div><div><span class="lit" style="color: rgb(0, 102, 102);">17</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/pci.h></span></div><div><span class="lit" style="color: rgb(0, 102, 102);">18</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/gpio.h></span></div><div><span class="lit" style="color: rgb(0, 102, 102);">19</span><span class="pln"> </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">20</span><span class="pln"> </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">21</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#define</span><span class="pln"> DEVICE_NAME </span><span class="str" style="color: rgb(0, 136, 0);">"mymap"</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">22</span><span class="pln"> </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">23</span><span class="pln"> </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">24</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">static</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">unsigned</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">char</span><span class="pln"> array</span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="lit" style="color: rgb(0, 102, 102);">10</span><span class="pun" style="color: rgb(102, 102, 0);">]={</span><span class="lit" style="color: rgb(0, 102, 102);">0</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">1</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">2</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">3</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">4</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">5</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">6</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">7</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">8</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="lit" style="color: rgb(0, 102, 102);">9</span><span class="pun" style="color: rgb(102, 102, 0);">};</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">25</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">static</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">unsigned</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">char</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">*</span><span class="pln">buffer</span><span class="pun" style="color: rgb(102, 102, 0);">;</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">26</span><span class="pln"> </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">27</span><span class="pln"> </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">28</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">static</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln"> my_open</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">struct</span><span class="pln"> inode </span><span class="pun" style="color: rgb(102, 102, 0);">*</span><span class="pln">inode</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">struct</span><span class="pln"> file </span><span class="pun" style="color: rgb(102, 102, 0);">*</span><span class="pln">file</span><span class="pun" style="color: rgb(102, 102, 0);">)</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">29</span><span class="pln"> </span><span class="pun" 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class="pln"> page</span><span class="pun" style="color: rgb(102, 102, 0);">;</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">37</span><span class="pln">     </span><span class="kwd" style="color: rgb(0, 0, 136);">unsigned</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">char</span><span class="pln"> i</span><span class="pun" style="color: rgb(102, 102, 0);">;</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">38</span><span class="pln">     </span><span class="kwd" style="color: rgb(0, 0, 136);">unsigned</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">long</span><span class="pln"> start </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">unsigned</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">long</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln">vma</span><span class="pun" style="color: rgb(102, 102, 0);">-></span><span class="pln">vm_start</span><span class="pun" style="color: rgb(102, 102, 0);">;</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">39</span><span class="pln">     </span><span class="com" style="color: rgb(136, 0, 0);">//unsigned long end =  (unsigned long)vma->vm_end;</span></div><div><span class="com" style="color: rgb(136, 0, 0);">40     unsigned long size = (unsigned long)(vma->vm_end - vma->vm_start);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">41 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">42     //得到物理地址</span></div><div><span class="com" style="color: rgb(136, 0, 0);">43     page = virt_to_phys(buffer);    </span></div><div><span class="com" style="color: rgb(136, 0, 0);">44     //将用户空间的一个vma虚拟内存区映射到以page开始的一段连续物理页面上</span></div><div><span class="com" style="color: rgb(136, 0, 0);">45     if(remap_pfn_range(vma,start,page>>PAGE_SHIFT,size,PAGE_SHARED))//第三个参数是页帧号，由物理地址右移PAGE_SHIFT得到</span></div><div><span class="com" style="color: rgb(136, 0, 0);">46         return -1; </span></div><div><span class="com" style="color: rgb(136, 0, 0);">47 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">48     //往该内存写10字节数据</span></div><div><span class="com" style="color: rgb(136, 0, 0);">49     for(i=0;i<10;i++)</span></div><div><span class="com" style="color: rgb(136, 0, 0);">50         buffer[i] = array[i];</span></div><div><span class="com" style="color: rgb(136, 0, 0);">51     </span></div><div><span class="com" style="color: rgb(136, 0, 0);">52     return 0;</span></div><div><span class="com" style="color: rgb(136, 0, 0);">53 }</span></div><div><span class="com" style="color: rgb(136, 0, 0);">54 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">55 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">56 static struct file_operations dev_fops = {</span></div><div><span class="com" style="color: rgb(136, 0, 0);">57     .owner    = THIS_MODULE,</span></div><div><span class="com" style="color: rgb(136, 0, 0);">58     .open    = my_open,</span></div><div><span class="com" style="color: rgb(136, 0, 0);">59     .mmap   = my_map,</span></div><div><span class="com" style="color: rgb(136, 0, 0);">60 };</span></div><div><span class="com" style="color: rgb(136, 0, 0);">61 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">62 static struct miscdevice misc = {</span></div><div><span class="com" style="color: rgb(136, 0, 0);">63     .minor = MISC_DYNAMIC_MINOR,</span></div><div><span class="com" style="color: rgb(136, 0, 0);">64     .name = DEVICE_NAME,</span></div><div><span class="com" style="color: rgb(136, 0, 0);">65     .fops = &dev_fops,</span></div><div><span class="com" style="color: rgb(136, 0, 0);">66 };</span></div><div><span class="com" style="color: rgb(136, 0, 0);">67 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">68 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">69 static int __init dev_init(void)</span></div><div><span class="com" style="color: rgb(136, 0, 0);">70 {</span></div><div><span class="com" style="color: rgb(136, 0, 0);">71     int ret;    </span></div><div><span class="com" style="color: rgb(136, 0, 0);">72 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">73     //注册混杂设备</span></div><div><span class="com" style="color: rgb(136, 0, 0);">74     ret = misc_register(&misc);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">75     //内存分配</span></div><div><span class="com" style="color: rgb(136, 0, 0);">76     buffer = (unsigned char *)kmalloc(PAGE_SIZE,GFP_KERNEL);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">77     //将该段内存设置为保留</span></div><div><span class="com" style="color: rgb(136, 0, 0);">78     SetPageReserved(virt_to_page(buffer));</span></div><div><span class="com" style="color: rgb(136, 0, 0);">79 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">80     return ret;</span></div><div><span class="com" style="color: rgb(136, 0, 0);">81 }</span></div><div><span class="com" style="color: rgb(136, 0, 0);">82 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">83 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">84 static void __exit dev_exit(void)</span></div><div><span class="com" style="color: rgb(136, 0, 0);">85 {</span></div><div><span class="com" style="color: rgb(136, 0, 0);">86     //注销设备</span></div><div><span class="com" style="color: rgb(136, 0, 0);">87     misc_deregister(&misc);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">88     //清除保留</span></div><div><span class="com" style="color: rgb(136, 0, 0);">89     ClearPageReserved(virt_to_page(buffer));</span></div><div><span class="com" style="color: rgb(136, 0, 0);">90     //释放内存</span></div><div><span class="com" style="color: rgb(136, 0, 0);">91     kfree(buffer);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">92 }</span></div><div><span class="com" style="color: rgb(136, 0, 0);">93 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">94 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">95 module_init(dev_init);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">96 module_exit(dev_exit);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">97 MODULE_LICENSE("GPL");</span></div><div><span class="com" style="color: rgb(136, 0, 0);">98 MODULE_AUTHOR("LKN@SCUT");</span></div><div><span class="com" style="color: rgb(136, 0, 0);"> </span></div><p style="margin-top: 0px; margin-bottom: 10px; padding-top: 0px; padding-bottom: 0px;"></p>

应用程序：

<p style="margin-top: 0px; margin-bottom: 10px; padding-top: 0px; padding-bottom: 0px;"></p><div></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">1</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><unistd.h></span><span class="pln"> </span></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">2</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><stdio.h></span></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">3</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><stdlib.h></span></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">4</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><string.h></span></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">5</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><fcntl.h></span></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">6</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><linux/fb.h></span></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">7</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><sys/mman.h></span></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">8</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln"> </span><span class="str" style="color: rgb(0, 136, 0);"><sys/ioctl.h></span><span class="pln"> </span></div><div><span class="pln"> </span><span class="lit" style="color: rgb(0, 102, 102);">9</span><span class="pln">     </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">10</span><span class="pln"> </span><span class="com" style="color: rgb(136, 0, 0);">#define</span><span class="pln"> PAGE_SIZE </span><span class="lit" style="color: rgb(0, 102, 102);">4096</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">11</span><span class="pln"> </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">12</span><span class="pln"> </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">13</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln"> main</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln"> argc </span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">char</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">*</span><span class="pln">argv</span><span class="pun" style="color: rgb(102, 102, 0);">[])</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">14</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">15</span><span class="pln">     </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln"> fd</span><span class="pun" style="color: rgb(102, 102, 0);">;</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">16</span><span class="pln">     </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln"> i</span><span class="pun" style="color: rgb(102, 102, 0);">;</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">17</span><span class="pln">     </span><span class="kwd" style="color: rgb(0, 0, 136);">unsigned</span><span class="pln"> </span><span class="kwd" style="color: rgb(0, 0, 136);">char</span><span class="pln"> </span><span class="pun" style="color: rgb(102, 102, 0);">*</span><span class="pln">p_map</span><span class="pun" style="color: rgb(102, 102, 0);">;</span></div><div><span class="lit" style="color: rgb(0, 102, 102);">18</span><span class="pln">     </span></div><div><span class="lit" style="color: rgb(0, 102, 102);">19</span><span class="pln">     </span><span class="com" style="color: rgb(136, 0, 0);">//打开设备</span></div><div><span class="com" style="color: rgb(136, 0, 0);">20     fd = open("/dev/mymap",O_RDWR);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">21     if(fd < 0)</span></div><div><span class="com" style="color: rgb(136, 0, 0);">22     {</span></div><div><span class="com" style="color: rgb(136, 0, 0);">23         printf("open fail\n");</span></div><div><span class="com" style="color: rgb(136, 0, 0);">24         exit(1);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">25     }</span></div><div><span class="com" style="color: rgb(136, 0, 0);">26 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">27     //内存映射</span></div><div><span class="com" style="color: rgb(136, 0, 0);">28     p_map = (unsigned char *)mmap(0, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,fd, 0);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">29     if(p_map == MAP_FAILED)</span></div><div><span class="com" style="color: rgb(136, 0, 0);">30     {</span></div><div><span class="com" style="color: rgb(136, 0, 0);">31         printf("mmap fail\n");</span></div><div><span class="com" style="color: rgb(136, 0, 0);">32         goto here;</span></div><div><span class="com" style="color: rgb(136, 0, 0);">33     }  </span></div><div><span class="com" style="color: rgb(136, 0, 0);">34 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">35     //打印映射后的内存中的前10个字节内容</span></div><div><span class="com" style="color: rgb(136, 0, 0);">36     for(i=0;i<10;i++)</span></div><div><span class="com" style="color: rgb(136, 0, 0);">37         printf("%d\n",p_map[i]);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">38     </span></div><div><span class="com" style="color: rgb(136, 0, 0);">39 </span></div><div><span class="com" style="color: rgb(136, 0, 0);">40 here:</span></div><div><span class="com" style="color: rgb(136, 0, 0);">41     munmap(p_map, PAGE_SIZE);</span></div><div><span class="com" style="color: rgb(136, 0, 0);">42     return 0;</span></div><div><span class="com" style="color: rgb(136, 0, 0);">43 }</span></div>