What changes need to be made to newgetpid.c to allow it to respond to write requests? Hint: How does newgetpid.c respond to read requests?

/* Code derived from: https://appusajeev.wordpress.com/2011/06/18/writing-a-linux-character-device-driver/ and http://pete.akeo.ie/2011/08/writing-linux-device-driver-for-kernels.html */

#include #include #include #include #include #include #include #include

#define dbg(format, arg...) do { if (debug) pr_info(CLASS_NAME ": %s: " format, __FUNCTION__, ## arg); } while (0) #define err(format, arg...) pr_err(CLASS_NAME ": " format, ## arg) #define info(format, arg...) pr_info(CLASS_NAME ": " format, ## arg) #define warn(format, arg...) pr_warn(CLASS_NAME ": " format, ## arg)

#define DEVICE_NAME "newgetpid" #define CLASS_NAME "comp3000"

static struct class* newgetpid_class = NULL; static struct device* newgetpid_device = NULL; static int newgetpid_major;

static int newgetpid_open(struct inode *the_inode, struct file *f) { return 0; }

static ssize_t newgetpid_read(struct file *f, char *buf, size_t len, loff_t *offset) { size_t i, msglen; pid_t thepid;

char message[100]; if (*offset > 0) { return 0; } thepid = task_tgid_vnr(current);

snprintf(message, 100, "Your PID is %d! ", thepid); msglen = strlen(message);

if (len < msglen) { msglen = len; }

for (i = 0; i < msglen; i++) { put_user(message[i], buf++); }

*offset = i;

return i; }

static int newgetpid_release(struct inode *the_inode, struct file *f) { printk(KERN_ALERT "Newgetpid device closed "); return 0; }

static struct file_operations newgetpid_fops = { .open = newgetpid_open, .read = newgetpid_read, .release = newgetpid_release, };

static char *newgetpid_devnode(struct device *dev, umode_t *mode) { if (mode) *mode = 0444; return NULL; }

static int __init newgetpid_init(void) { int retval; newgetpid_major = register_chrdev(0, DEVICE_NAME, &newgetpid_fops); if (newgetpid_major < 0) { err("failed to register device: error %d ", newgetpid_major); retval = newgetpid_major; goto failed_chrdevreg; } newgetpid_class = class_create(THIS_MODULE, CLASS_NAME); if (IS_ERR(newgetpid_class)) { err("failed to register device class '%s' ", CLASS_NAME); retval = PTR_ERR(newgetpid_class); goto failed_classreg; } newgetpid_class->devnode = newgetpid_devnode;

newgetpid_device = device_create(newgetpid_class, NULL, MKDEV(newgetpid_major, 0), NULL, DEVICE_NAME);

if (IS_ERR(newgetpid_device)) { err("failed to create device '%s' ", DEVICE_NAME); retval = PTR_ERR(newgetpid_device); goto failed_devreg; } info("Newgetpid device registered using major %d. ", newgetpid_major); return 0; failed_devreg: class_unregister(newgetpid_class); class_destroy(newgetpid_class); failed_classreg: unregister_chrdev(newgetpid_major, DEVICE_NAME); failed_chrdevreg: return -1; }

static void __exit newgetpid_exit(void) { device_destroy(newgetpid_class, MKDEV(newgetpid_major, 0)); class_unregister(newgetpid_class); class_destroy(newgetpid_class); unregister_chrdev(newgetpid_major, "newgetpid"); info("Unloading Newgetpid module. "); return; }

module_init(newgetpid_init); module_exit(newgetpid_exit);

MODULE_LICENSE("GPL"); MODULE_AUTHOR("Anil Somayaji "); MODULE_DESCRIPTION("A write newgetpid character device module");