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�XDyd 1 L1(资/料来.源,于:ｇzu５2１学;习/网:电脑课堂;LINUX教程 ]ｇzu５2１.ｃoｍ�XDyd 1 L1 这不是总能奏效的。设想你与一个连向modem的串口（技是你有一个内猫，从cpu看来它也是作为一个串口实现，所以你不需要认为这个设想太困难）。最自然要做的事情就是使用设备文件把内容写到modem上（无论用modem命令还是电话线）或者从modem读信息（同样可以从modem命令回答或者通过电话线）。但是这留下的问题是当你需要和串口本身对话的时候需要怎样做？比如发送数据发送和接收的速率。 回答是unix使用一个叫做ioctl(input output control的简写)的特殊函数。每个设备都有自己的ioctl命令，这个命令可以是ioctl读的，也可以是写的，也可以是两者都是或都不是。ioctl函数由三个参数调用：适当设备的描述子，ioctl数，和一个长整型参数，可以赋予一个角色用来传递任何东西。 ioctl数对设备主码、ioctl类型、编码、和参数的类型进行编码。ioctl数通常在头文件由一个宏调用（_io，_ior，_iow或_iowr——决定于类型）。这个头文件必须包含在使用ioctl（所以它们可以产生正确的ioctl’s）程序和内核模块（所以它可以理解）中。在下面的例子里，这个头文件是chardev.h，使用它的程序是ioctl.c。 如果你希望在你自己的内核模块中使用ioctl’s，最好去接受一分正式的ioctl职位，这样你就可以得到别人的ioctl’s，或者他们得到你，你就可以知道哪里出了错误。如果想得到更多的信息，到’documentation/ioctl-number.txt’中查看内核源文件树。 ex chardev.c /* chardev.c * * create an input/output character device */ /* copyright (c) 1998-99 by ori pomerantz */ /* the necessary header files */ /* standard in kernel modules */ #include /* were doing kernel work */ #include /* specifically, a module */ /* deal with config_modversions */ #if config_modversions==1 #define modversions #include #endif /* for character devices */ /* the character device definitions are here */ #include /* a wrapper which does next to nothing at * at present, but may help for compatibility * with future versions of linux */ #include /* our own ioctl numbers */ #include "chardev.h" /* in 2.2.3 /usr/include/linux/version.h includes a * macro for this, but 2.0.35 doesnt - so i add it * here if necessary. */ #ifndef kernel_version #define kernel_version(a,b,c) ((a)*65536+(b)*256+(c)) #endif #if linux_version_code >= kernel_version(2,2,0) #include /* for get_user and put_user */ #endif #define success 0 /* device declarations ******************************** */ /* the name for our device, as it will appear in * /proc/devices */ #define device_name "char_dev" /* the maximum length of the message for the device */ #define buf_len 80 /* is the device open right now? used to prevent * concurent access into the same device */ static int device_open = 0; C EfF H 来 源 于 贵 州学 习网 电脑课堂LINUX教程 WWw.gzU521.COm C EfF H /* the message the device will give when asked */ static char message[buf_len]; /* how far did the process reading the message get? * useful if the message is larger than the size of the * buffer we get to fill in device_read. */ static char *message_ptr; /* this function is called whenever a process attempts * to open the device file */ static int device_open(struct inode *inode, struct file *file) { #ifdef debug printk ("device_open(%p)\n", file); #endif /* we dont want to talk to two processes at the * same time */ if (device_open) return -ebusy; /* if this was a process, we would have had to be * more careful here, because one process might have * checked device_open right before the other one * tried to increment it. however, were in the * kernel, so were protected against context switches. * * this is not the right attitude to take, because we * might be running on an smp box, but well deal with * smp in a later chapter. */  |
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