I am using the following Kernel Device Driver.
/** * @file ebbchar.c * @author Derek Molloy * @date 7 April 2015 * @version 0.1 * @brief An introductory character driver to support the second article of my series on * Linux loadable kernel module (LKM) development. This module maps to /dev/ebbchar and * comes with a helper C program that can be run in Linux user space to communicate with * this the LKM. * @see http://www.derekmolloy.ie/ for a full description and follow-up descriptions. */ #include <linux/init.h> // Macros used to mark up functions e.g. __init __exit #include <linux/module.h> // Core header for loading LKMs into the kernel #include <linux/device.h> // Header to support the kernel Driver Model #include <linux/kernel.h> // Contains types, macros, functions for the kernel #include <linux/fs.h> // Header for the Linux file system support #include <asm/uaccess.h> // Required for the copy to user function #define DEVICE_NAME "ebbchar" ///< The device will appear at /dev/ebbchar using this value #define CLASS_NAME "ebb" ///< The device class -- this is a character device driver MODULE_LICENSE("GPL"); ///< The license type -- this affects available functionality MODULE_AUTHOR("Derek Molloy"); ///< The author -- visible when you use modinfo MODULE_DESCRIPTION("A simple Linux char driver for the BBB"); ///< The description -- see modinfo MODULE_VERSION("0.1"); ///< A version number to inform users static int majorNumber; ///< Stores the device number -- determined automatically static char message[256] = {0}; ///< Memory for the string that is passed from userspace static short size_of_message; ///< Used to remember the size of the string stored static int numberOpens = 0; ///< Counts the number of times the device is opened static struct class* ebbcharClass = NULL; ///< The device-driver class struct pointer static struct device* ebbcharDevice = NULL; ///< The device-driver device struct pointer // The prototype functions for the character driver -- must come before the struct definition static int dev_open(struct inode *, struct file *); static int dev_release(struct inode *, struct file *); static ssize_t dev_read(struct file *, char *, size_t, loff_t *); static ssize_t dev_write(struct file *, const char *, size_t, loff_t *); /** @brief Devices are represented as file structure in the kernel. The file_operations structure from * /linux/fs.h lists the callback functions that you wish to associated with your file operations * using a C99 syntax structure. char devices usually implement open, read, write and release calls */ static struct file_operations fops = { .open = dev_open, .read = dev_read, .write = dev_write, .release = dev_release, }; /** @brief The LKM initialization function * The static keyword restricts the visibility of the function to within this C file. The __init * macro means that for a built-in driver (not a LKM) the function is only used at initialization * time and that it can be discarded and its memory freed up after that point. * @return returns 0 if successful */ static int __init ebbchar_init(void){ printk(KERN_INFO "EBBChar: Initializing the EBBChar LKM\n"); // Try to dynamically allocate a major number for the device -- more difficult but worth it majorNumber = register_chrdev(0, DEVICE_NAME, &fops); if (majorNumber<0){ printk(KERN_ALERT "EBBChar failed to register a major number\n"); return majorNumber; } printk(KERN_INFO "EBBChar: registered correctly with major number %d\n", majorNumber); // Register the device class ebbcharClass = class_create(THIS_MODULE, CLASS_NAME); if (IS_ERR(ebbcharClass)){ // Check for error and clean up if there is unregister_chrdev(majorNumber, DEVICE_NAME); printk(KERN_ALERT "Failed to register device class\n"); return PTR_ERR(ebbcharClass); // Correct way to return an error on a pointer } printk(KERN_INFO "EBBChar: device class registered correctly\n"); // Register the device driver ebbcharDevice = device_create(ebbcharClass, NULL, MKDEV(majorNumber, 0), NULL, DEVICE_NAME); if (IS_ERR(ebbcharDevice)){ // Clean up if there is an error class_destroy(ebbcharClass); // Repeated code but the alternative is goto statements unregister_chrdev(majorNumber, DEVICE_NAME); printk(KERN_ALERT "Failed to create the device\n"); return PTR_ERR(ebbcharDevice); } printk(KERN_INFO "EBBChar: device class created correctly\n"); // Made it! device was initialized return 0; } /** @brief The LKM cleanup function * Similar to the initialization function, it is static. The __exit macro notifies that if this * code is used for a built-in driver (not a LKM) that this function is not required. */ static void __exit ebbchar_exit(void){ device_destroy(ebbcharClass, MKDEV(majorNumber, 0)); // remove the device class_unregister(ebbcharClass); // unregister the device class class_destroy(ebbcharClass); // remove the device class unregister_chrdev(majorNumber, DEVICE_NAME); // unregister the major number printk(KERN_INFO "EBBChar: Goodbye from the LKM!\n"); } /** @brief The device open function that is called each time the device is opened * This will only increment the numberOpens counter in this case. * @param inodep A pointer to an inode object (defined in linux/fs.h) * @param filep A pointer to a file object (defined in linux/fs.h) */ static int dev_open(struct inode *inodep, struct file *filep){ numberOpens++; printk(KERN_INFO "EBBChar: Device has been opened %d time(s)\n", numberOpens); return 0; } /** @brief This function is called whenever device is being read from user space i.e. data is * being sent from the device to the user. In this case is uses the copy_to_user() function to * send the buffer string to the user and captures any errors. * @param filep A pointer to a file object (defined in linux/fs.h) * @param buffer The pointer to the buffer to which this function writes the data * @param len The length of the b * @param offset The offset if required */ static ssize_t dev_read(struct file *filep, char *buffer, size_t len, loff_t *offset){ int error_count = 0; // copy_to_user has the format ( * to, *from, size) and returns 0 on success error_count = copy_to_user(buffer, message, size_of_message); if (error_count==0){ // if true then have success printk(KERN_INFO "EBBChar: Sent %d characters to the user\n", size_of_message); return (size_of_message=0); // clear the position to the start and return 0 } else { printk(KERN_INFO "EBBChar: Failed to send %d characters to the user\n", error_count); return -EFAULT; // Failed -- return a bad address message (i.e. -14) } } /** @brief This function is called whenever the device is being written to from user space i.e. * data is sent to the device from the user. The data is copied to the message[] array in this * LKM using the sprintf() function along with the length of the string. * @param filep A pointer to a file object * @param buffer The buffer to that contains the string to write to the device * @param len The length of the array of data that is being passed in the const char buffer * @param offset The offset if required */ static ssize_t dev_write(struct file *filep, const char *buffer, size_t len, loff_t *offset){ sprintf(message, "%s(%zu letters)", buffer, len); // appending received string with its length size_of_message = strlen(message); // store the length of the stored message printk(KERN_INFO "EBBChar: Received %zu characters from the user\n", len); return len; } /** @brief The device release function that is called whenever the device is closed/released by * the userspace program * @param inodep A pointer to an inode object (defined in linux/fs.h) * @param filep A pointer to a file object (defined in linux/fs.h) */ static int dev_release(struct inode *inodep, struct file *filep){ printk(KERN_INFO "EBBChar: Device successfully closed\n"); return 0; } /** @brief A module must use the module_init() module_exit() macros from linux/init.h, which * identify the initialization function at insertion time and the cleanup function (as * listed above) */ module_init(ebbchar_init); module_exit(ebbchar_exit); When I open the device driver in User Space, the dev_open() function is executed.
static struct file_operations fops = { .open = dev_open, .read = dev_read, .write = dev_write, .release = dev_release, }; static int dev_open(struct inode *inodep, struct file *filep){ numberOpens++; printk(KERN_INFO "EBBChar: Device has been opened %d time(s)\n", numberOpens); return 0; } I want to know who has open() the Device Driver node (/dev/ebbchar).
When a process calls the dev_open() function of the device driver, I want to debug the process name via printk().
What should I do?
