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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><HTML><HEAD> <TITLE>高级 I/O</TITLE> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=gb2312-80"> <META NAME="COPYRIGHT" CONTENT="魏永明"> <META NAME="AUTHOR" CONTENT="魏永明"> <STYLE> <!-- H1 { color: #ffff00 } H2 { color: #ffff00 } H3 { color: #ff00ff } H4 { color: #ffff00 } TD P { color: #b880b8 } LI { color: #ffffff } P { color: #00ffff } PRE { color: #ffffff; font-family: "fixed" } A:link { color: #00b8ff } A:visited { color: #ff3366 } --> </STYLE></HEAD><BODY TEXT="#ffff00" LINK="#00b8ff" VLINK="#ff3366" BACKGROUND="images/velvet.jpg"><A HREF="dir.html"><IMG SRC="prev.gif" ALT="Previous"></A><A HREF="misc.html"><IMG SRC="next.gif" ALT="Next"></A><A HREF="index.html"><IMG SRC="toc.gif" ALT="Contents"></A><H1 ALIGN=CENTER>5.5 高级 I/O<BR><BR></H1><UL> <LI><P>Linux 中直接的 I/O 端口读写</LI> <LI><P>记录锁定</LI> <LI><P>非阻塞 I/O</LI> <LI><P>I/O 多工</LI> <LI><P>异步 I/O</LI> <LI><P>内存映射</LI></UL><H3>5.5.1 Linux 中直接的 I/O 端口读写</H3><UL> <LI>只有 root 进程才能直接访问 I/O 端口</LI> <LI>首先要取得端口的访问权限: ioperm, iopl</LI> <LI>然后才能用 inb 和 outb</LI> <LI>inb 和 outb 以内嵌函数的形式实现, 因此要用 -O 或 -O2 选项编译</LI></UL><PRE>=============================================================================== #include <unistd.h> /* for libc5 */ #include <sys/io.h> /* for glibc */ int ioperm (unsigned long from, unsigned long num, int turn_on); int iopl (int level);-------------------------------------------------------------------------------EXAMPLE: /* get PC speak I/O ports access permission and implement a beep function */ #define COUNTER_ADDR 0x61 int beepCount = 500000; BOOL InitIOPerm () { if (ioperm (COUNTER_ADDR, 1, TRUE)) { fprintf (stderr, "Can not get beep I/O permission!\n"); return FALSE; } return TRUE; } void CleanupIOPerm () { ioperm (COUNTER_ADDR, 1, FALSE); } void GUIAPI Beep (void) { outb (inb (COUNTER_ADDR) | 3, COUNTER_ADDR); usleep (beepCount); outb (inb (COUNTER_ADDR) & 0xFC, COUNTER_ADDR); }===============================================================================</PRE><H3>5.5.2 记录锁定</H3><UL> <LI>基本概念</LI> <LI>#自学#</LI></UL><H3>5.5.3 非阻塞 I/O</H3><UL> <LI>基本概念</LI> <LI>open 时可指定 O_NONBLOCK (O_NDELAY)</LI> <LI>用 fcntl 设置描述符标志而改变为非阻塞</LI></UL><H3>5.5.4 I/O 多工</H3><UL> <LI>基本概念</LI> <LI>select 和 poll</LI></UL><PRE>=============================================================================== #include <sys/time.h> #include <sys/types.h> #include <unistd.h> int select (int n, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout); FD_CLR (int fd, fd_set *set); FD_ISSET (int fd, fd_set *set); FD_SET (int fd, fd_set *set); FD_ZERO (fd_set *set); #include <sys/poll.h> int poll(struct pollfd *ufds, unsigned int nfds, int timeout);------------------------------------------------------------------------------- struct pollfd { int fd; /* file descriptor */ short events; /* requested events */ short revents; /* returned events */ };------------------------------------------------------------------------------- * select 中的 n 是所等待文件描述符中最大的值加 1.-------------------------------------------------------------------------------EXAMPLE 1: /* 在 Virtual Console on MiniGUI 中, 我们用 poll 等待主伪终端上的数据 */ void ReadMasterPty (PCONINFO con) { BYTE buff [BUFSIZ + 1]; int nRead; struct pollfd fd = {con->masterPty, POLLIN, 0}; int ret; ret = poll (&fd, 1, 10); // about 0.01s if (ret == 0) { return; } else if (ret > 0) { if ((nRead = read (con->masterPty, buff, BUFSIZ)) > 0) { VtWrite (con, buff, nRead); TextRefresh (con, true); } } } /* 如果没有数据, 我们处理 MiniGUI 的消息, 包括键盘和鼠标事件 */ ... // Enter message loop. do { // It is time to read from master pty, and output. ReadMasterPty (pConInfo); if (pConInfo->terminate) break; while (HavePendingMessage (hMainWnd)) { if (!GetMessage (&Msg, hMainWnd)) break; DispatchMessage (&Msg); } } while (TRUE); ... /* 我们也可以用非阻塞 I/O 实现 ReadMasterPty, 但这种方法非常消耗 CPU 资源 */-------------------------------------------------------------------------------EXAMPLE 1: /* SVGALib 用 select 函数实现 vga_waitevent 函数等待键盘和鼠标事件 */ int vga_waitevent(int which, fd_set * in, fd_set * out, fd_set * except, struct timeval *timeout) { fd_set infdset; int fd, retval; if (!in) { in = &infdset; FD_ZERO(in); } fd = __svgalib_mouse_fd; /* __svgalib_mouse_fd might change on vc switch!! */ if ((which & VGA_MOUSEEVENT) && (fd >= 0)) FD_SET(fd, in); if (which & VGA_KEYEVENT) { fd = __svgalib_kbd_fd; if (fd >= 0) { /* we are in raw mode */ FD_SET(fd, in); } else { FD_SET(__svgalib_tty_fd, in); } } if (select(FD_SETSIZE, in, out, except, timeout) < 0) return -1; retval = 0; fd = __svgalib_mouse_fd; if ((which & VGA_MOUSEEVENT) && (fd >= 0)) { if (FD_ISSET(fd, in)) { retval |= VGA_MOUSEEVENT; FD_CLR(fd, in); mouse_update(); } } if (which & VGA_KEYEVENT) { fd = __svgalib_kbd_fd; if (fd >= 0) { /* we are in raw mode */ if (FD_ISSET(fd, in)) { FD_CLR(fd, in); retval |= VGA_KEYEVENT; keyboard_update(); } } else if (FD_ISSET(__svgalib_tty_fd, in)) { FD_CLR(__svgalib_tty_fd, in); retval |= VGA_KEYEVENT; } } return retval; }===============================================================================</PRE><H3>5.5.4 异步 I/O</H3><UL> <LI>基本概念</LI> <LI>#自学#</LI></UL><H3>5.5.5 内存映射</H3><UL> <LI>基本概念</LI> <LI>mmap/unmmap</LI><PRE>=============================================================================== #include <unistd.h> #include <sys/mman.h> #ifdef _POSIX_MAPPED_FILES void* mmap (void *start, size_t length, int prot, int flags, int fd, off_t offset); int munmap (void *start, size_t length); #endif------------------------------------------------------------------------------- * mmap 的 start 一般设为 0, 由系统决定选择什么地址作为起始的映射地址. * prot 的取值必须和 fd 的打开标志一直. * 写时复制的含义.-------------------------------------------------------------------------------SAMPLE: /* 打开一个文件, 利用 mmap 将文件反序保存 为简单起见, 只处理文件的前 10 个字符 */ #include <stdio.h> #include <unistd.h> #include <sys/mman.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int main (int args, char* arg[]) { int i; int fd; char* mem; if ((fd = open ("temp", O_RDWR)) < 0) { perror ("open error"); return -1; } mem = mmap (0, 10, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, 0); if (mem == MAP_FAILED) { perror ("mmap error:"); return 1; } for (i = 0; i < 5; i++) { char temp; temp = mem [i]; mem [i] = mem [9 - i]; mem [9 - i] = temp; } munmap (mem, 10); close (fd); return 0; }===============================================================================</PRE></UL><P><BR><BR></P><P ALIGN=CENTER><IMG SRC="images/striped.gif" NAME="Ruler" ALIGN=BOTTOM WIDTH=532 HEIGHT=13 BORDER=0></P><P><BR><BR></P><A HREF="dir.html"><IMG SRC="prev.gif" ALT="Previous"></A><A HREF="misc.html"><IMG SRC="next.gif" ALT="Next"></A><A HREF="index.html"><IMG SRC="toc.gif" ALT="Contents"></A></BODY></HTML>⌨️ 快捷键说明
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