7.1. Talking to Device Files (writes and IOCTLs)

Device files are supposed to represent physical devices. Most physical devices are used for output as well as input, so there has to be some mechanism for device drivers in the kernel to get the output to send to the device from processes. This is done by opening the device file for output and writing to it, just like writing to a file. In the following example, this is implemented by device_write.

This is not always enough. Imagine you had a serial port connected to a modem (even if you have an internal modem, it is still implemented from the CPU's perspective as a serial port connected to a modem, so you don't have to tax your imagination too hard). The natural thing to do would be to use the device file to write things to the modem (either modem commands or data to be sent through the phone line) and read things from the modem (either responses for commands or the data received through the phone line). However, this leaves open the question of what to do when you need to talk to the serial port itself, for example to send the rate at which data is sent and received.

The answer in Unix is to use a special function called ioctl (short for Input Output ConTroL). Every device can have its own ioctl commands, which can be read ioctl's (to send information from a process to the kernel), write ioctl's (to return information to a process), [1] both or neither. The ioctl function is called with three parameters: the file descriptor of the appropriate device file, the ioctl number, and a parameter, which is of type long so you can use a cast to use it to pass anything. [2]

The ioctl number encodes the major device number, the type of the ioctl, the command, and the type of the parameter. This ioctl number is usually created by a macro call (_IO, _IOR, _IOW or _IOWR --- depending on the type) in a header file. This header file should then be included both by the programs which will use ioctl (so they can generate the appropriate ioctl's) and by the kernel module (so it can understand it). In the example below, the header file is chardev.h and the program which uses it is ioctl.c.

If you want to use ioctls in your own kernel modules, it is best to receive an official ioctl assignment, so if you accidentally get somebody else's ioctls, or if they get yours, you'll know something is wrong. For more information, consult the kernel source tree at Documentation/ioctl-number.txt.

Example 7-1. chardev.c

/* a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html chardev.c - Create an input/output character device figures/ #include <linux/kernel.h> /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var We're doing kernel work figures/ #include <linux/module.h> /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var Specifically, a module figures/ #include <linux/fs.h> #include <asm/uaccess.h> /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var for get_user and put_user figures/ #include "chardev.h" #define SUCCESS 0 #define DEVICE_NAME "char_dev" #define BUF_LEN 80 /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Is the device open right now? Used to prevent a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html concurent access into the same device figures/ static int Device_Open = 0; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html The message the device will give when asked figures/ static char Message[BUF_LEN]; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html How far did the process reading the message get? a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Useful if the message is larger than the size of the a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html buffer we get to fill in device_read. figures/ static char *Message_Ptr; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html This is called whenever a process attempts to open the device file figures/ static int device_open(struct inode *inode, struct file *file) { #ifdef DEBUG printk(KERN_INFO "device_open(%p)\n", file); #endif /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html We don't want to talk to two processes at the same time figures/ if (Device_Open) return -EBUSY; Device_Open++; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Initialize the message figures/ Message_Ptr = Message; try_module_get(THIS_MODULE); return SUCCESS; } static int device_release(struct inode *inode, struct file *file) { #ifdef DEBUG printk(KERN_INFO "device_release(%p,%p)\n", inode, file); #endif /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html We're now ready for our next caller figures/ Device_Open--; module_put(THIS_MODULE); return SUCCESS; } /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html This function is called whenever a process which has already opened the a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html device file attempts to read from it. figures/ static ssize_t device_read(struct file *file, /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var see include/linux/fs.h figures/ char __user a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html buffer, /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var buffer to be a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html filled with data figures/ size_t length, /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var length of the buffer figures/ loff_t a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html offset) { /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Number of bytes actually written to the buffer figures/ int bytes_read = 0; #ifdef DEBUG printk(KERN_INFO "device_read(%p,%p,%d)\n", file, buffer, length); #endif /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html If we're at the end of the message, return 0 a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html (which signifies end of file) figures/ if (*Message_Ptr == 0) return 0; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Actually put the data into the buffer figures/ while (length && *Message_Ptr) { /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Because the buffer is in the user data segment, a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html not the kernel data segment, assignment wouldn't a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html work. Instead, we have to use put_user which a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html copies data from the kernel data segment to the a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html user data segment. figures/ put_user(*(Message_Ptr++), buffer++); length--; bytes_read++; } #ifdef DEBUG printk(KERN_INFO "Read %d bytes, %d left\n", bytes_read, length); #endif /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Read functions are supposed to return the number a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html of bytes actually inserted into the buffer figures/ return bytes_read; } /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html This function is called when somebody tries to a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html write into our device file. figures/ static ssize_t device_write(struct file *file, const char __user a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html buffer, size_t length, loff_t a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html offset) { int i; #ifdef DEBUG printk(KERN_INFO "device_write(%p,%s,%d)", file, buffer, length); #endif for (i = 0; i < length && i < BUF_LEN; i++) get_user(Message[i], buffer + i); Message_Ptr = Message; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Again, return the number of input characters used figures/ return i; } /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html This function is called whenever a process tries to do an ioctl on our a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html device file. We get two extra parameters (additional to the inode and file a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html structures, which all device functions get): the number of the ioctl called a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html and the parameter given to the ioctl function. a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html If the ioctl is write or read/write (meaning output is returned to the a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html calling process), the ioctl call returns the output of this function. a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html figures/ int device_ioctl(struct inode *inode, /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var see include/linux/fs.h figures/ struct file *file, /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var ditto figures/ unsigned int ioctl_num, /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var number and param for ioctl figures/ unsigned long ioctl_param) { int i; char *temp; char ch; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Switch according to the ioctl called figures/ switch (ioctl_num) { case IOCTL_SET_MSG: /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Receive a pointer to a message (in user space) and set that a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html to be the device's message. Get the parameter given to a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html ioctl by the process. figures/ temp = (char *)ioctl_param; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Find the length of the message figures/ get_user(ch, temp); for (i = 0; ch && i < BUF_LEN; i++, temp++) get_user(ch, temp); device_write(file, (char *)ioctl_param, i, 0); break; case IOCTL_GET_MSG: /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Give the current message to the calling process - a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html the parameter we got is a pointer, fill it. figures/ i = device_read(file, (char *)ioctl_param, 99, 0); /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Put a zero at the end of the buffer, so it will be a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html properly terminated figures/ put_user('\0', (char *)ioctl_param + i); break; case IOCTL_GET_NTH_BYTE: /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html This ioctl is both input (ioctl_param) and a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html output (the return value of this function) figures/ return Message[ioctl_param]; break; } return SUCCESS; } /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var Module Declarations figures/ /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html This structure will hold the functions to be called a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html when a process does something to the device we a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html created. Since a pointer to this structure is kept in a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html the devices table, it can't be local to a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html init_module. NULL is for unimplemented functions. figures/ struct file_operations Fops = { .read = device_read, .write = device_write, .ioctl = device_ioctl, .open = device_open, .release = device_release, /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a.k.a. close figures/ }; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Initialize the module - Register the character device figures/ int init_module() { int ret_val; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Register the character device (atleast try) figures/ ret_val = register_chrdev(MAJOR_NUM, DEVICE_NAME, &Fops); /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Negative values signify an error figures/ if (ret_val < 0) { printk(KERN_ALERT "%s failed with %d\n", "Sorry, registering the character device ", ret_val); return ret_val; } printk(KERN_INFO "%s The major device number is %d.\n", "Registeration is a success", MAJOR_NUM); printk(KERN_INFO "If you want to talk to the device driver,\n"); printk(KERN_INFO "you'll have to create a device file. \n"); printk(KERN_INFO "We suggest you use:\n"); printk(KERN_INFO "mknod %s c %d 0\n", DEVICE_FILE_NAME, MAJOR_NUM); printk(KERN_INFO "The device file name is important, because\n"); printk(KERN_INFO "the ioctl program assumes that's the\n"); printk(KERN_INFO "file you'll use.\n"); return 0; } /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Cleanup - unregister the appropriate file from /proc figures/ void cleanup_module() { int ret; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Unregister the device figures/ ret = unregister_chrdev(MAJOR_NUM, DEVICE_NAME); /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html If there's an error, report it figures/ if (ret < 0) printk(KERN_ALERT "Error: unregister_chrdev: %d\n", ret); }

Example 7-2. chardev.h

/* a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html chardev.h - the header file with the ioctl definitions. a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html The declarations here have to be in a header file, because a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html they need to be known both to the kernel module a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html (in chardev.c) and the process calling ioctl (ioctl.c) figures/ #ifndef CHARDEV_H #define CHARDEV_H #include <linux/ioctl.h> /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html The major device number. We can't rely on dynamic a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html registration any more, because ioctls need to know a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html it. figures/ #define MAJOR_NUM 100 /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Set the message of the device driver figures/ #define IOCTL_SET_MSG _IOR(MAJOR_NUM, 0, char *) /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html _IOR means that we're creating an ioctl command a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html number for passing information from a user process a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html to the kernel module. a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html The first arguments, MAJOR_NUM, is the major device a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html number we're using. a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html The second argument is the number of the command a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html (there could be several with different meanings). a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html The third argument is the type we want to get from a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html the process to the kernel. figures/ /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Get the message of the device driver figures/ #define IOCTL_GET_MSG _IOR(MAJOR_NUM, 1, char *) /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html This IOCTL is used for output, to get the message a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html of the device driver. However, we still need the a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html buffer to place the message in to be input, a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html as it is allocated by the process. figures/ /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Get the n'th byte of the message figures/ #define IOCTL_GET_NTH_BYTE _IOWR(MAJOR_NUM, 2, int) /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html The IOCTL is used for both input and output. It a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html receives from the user a number, n, and returns a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Message[n]. figures/ /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html The name of the device file figures/ #define DEVICE_FILE_NAME "char_dev" #endif

Example 7-3. ioctl.c

/* a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html ioctl.c - the process to use ioctl's to control the kernel module a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Until now we could have used cat for input and output. But now a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html we need to do ioctl's, which require writing our own process. figures/ /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html device specifics, such as ioctl numbers and the a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html major device file. figures/ #include "chardev.h" #include <stdio.h> #include <stdlib.h> #include <fcntl.h> /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var open figures/ #include <unistd.h> /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var exit figures/ #include <sys/ioctl.h> /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var ioctl figures/ /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Functions for the ioctl calls figures/ ioctl_set_msg(int file_desc, char *message) { int ret_val; ret_val = ioctl(file_desc, IOCTL_SET_MSG, message); if (ret_val < 0) { printf("ioctl_set_msg failed:%d\n", ret_val); exit(-1); } } ioctl_get_msg(int file_desc) { int ret_val; char message[100]; /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Warning - this is dangerous because we don't tell a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html the kernel how far it's allowed to write, so it a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html might overflow the buffer. In a real production a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html program, we would have used two ioctls - one to tell a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html the kernel the buffer length and another to give a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html it the buffer to fill figures/ ret_val = ioctl(file_desc, IOCTL_GET_MSG, message); if (ret_val < 0) { printf("ioctl_get_msg failed:%d\n", ret_val); exit(-1); } printf("get_msg message:%s\n", message); } ioctl_get_nth_byte(int file_desc) { int i; char c; printf("get_nth_byte message:"); i = 0; do { c = ioctl(file_desc, IOCTL_GET_NTH_BYTE, i++); if (c < 0) { printf ("ioctl_get_nth_byte failed at the %d'th byte:\n", i); exit(-1); } putchar(c); } while (c != 0); putchar('\n'); } /apps /backup /bin /boot /data /dev /etc /home /lib /lost+found /media /misc /mnt /net /opt /proc /root /sbin /selinux /srv /sys /tftpboot /tmp /usr /var a1387.htm a1387.html a1403.htm a1403.html book1.htm c1050.htm c1050.html c1159.htm c1159.html c119.htm c119.html c1209.htm c1209.html c1254.htm c1324.htm c1324.html c1350.htm c1350.html c38.htm c38.html c425.htm c425.html c567.htm c567.html c708.htm c708.html c885.htm c885.html c890.htm c890.html c976.htm c976.html doc-index.html f25.htm f25.html figures hello2.html i1413.htm index.html interrupthandlers.html ln16.html TXT_lkmpg.html x1052.html x1161.html x1194.htm x1194.html x1211.html x121.html x1256.html x1326.html x1352.html x1389.html x1405.html x181.htm x181.html x217.htm x245.htm x245.html x279.htm x279.html x27.html x30.htm x30.html x323.htm x323.html x351.htm x351.html x35.htm x35.html x380.htm x380.html x40.html x427.html x44.htm x44.html x569.html x710.html x769.htm x769.html x810.htm x810.html x861.htm x861.html x887.html x892.html x978.html Main - Call the ioctl functions figures/ main() { int file_desc, ret_val; char *msg = "Message passed by ioctl\n"; file_desc = open(DEVICE_FILE_NAME, 0); if (file_desc < 0) { printf("Can't open device file: %s\n", DEVICE_FILE_NAME); exit(-1); } ioctl_get_nth_byte(file_desc); ioctl_get_msg(file_desc); ioctl_set_msg(file_desc, msg); close(file_desc); }

Notes

[1]

Notice that here the roles of read and write are reversed again, so in ioctl's read is to send information to the kernel and write is to receive information from the kernel.

[2]

This isn't exact. You won't be able to pass a structure, for example, through an ioctl --- but you will be able to pass a pointer to the structure.