Im trying to write a driver device in linux where it is a stack of 10bytes. When the device is written into, the stack will push only ASCII lower case onto the stack i.e (97-122) and store them from the buffer. Here is what I have so far, and so the only thing i think that would need to be modify is the ssize_t memory_write method. I am confuse on how to access the string from the buffer and storing it.

/* Necessary includes for device drivers */

#include

#include "/usr/src/linux-headers-4.13.0-16-generic/include/linux/configfs.h"

#include

#include /* printk() */

#include /* kmalloc() */

#include /* everything... */

#include /* error codes */

#include /* size_t */

#include

#include /* O_ACCMODE */

//#include /* cli(), *_flags */

#include "/usr/src/linux-headers-4.13.0-16-generic/include/linux/uaccess.h" /* copy_from/to_user */

MODULE_LICENSE("Dual BSD/GPL");

/* Declaration of memory.c functions */

int memory_open(struct inode *inode, struct file *filp);

int memory_release(struct inode *inode, struct file *filp);

ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);

ssize_t memory_write(struct file *filp, const char *buf, size_t count, loff_t *f_pos);

void memory_exit(void);

int memory_init(void);

/* Structure that declares the usual file */

/* access functions */

struct file_operations memory_fops = {

read: memory_read,

.write= memory_write,

open: memory_open,

release: memory_release

};

/* Declaration of the init and exit functions */

module_init(memory_init);

module_exit(memory_exit);

/* Global variables of the driver */

/* Major number */

int memory_major = 60;

/* Buffer to store data */

char *memory_buffer;

int memory_init(void) {

int result;

/* Registering device */

result = register_chrdev(memory_major, "memory", &memory_fops);

if (result < 0) {

printk(

"<1>memory: cannot obtain major number %d ", memory_major);

return result;

}

/* Allocating memory for the buffer */

memory_buffer = kmalloc(10, GFP_KERNEL);

if (!memory_buffer) {

result = -ENOMEM;

goto fail;

}

memset(memory_buffer, 0, 10);

printk("<1>Inserting memory module ");

return 0;

fail:

memory_exit();

return result;

}

void memory_exit(void) {

/* Freeing the major number */

unregister_chrdev(memory_major, "memory");

/* Freeing buffer memory */

if (memory_buffer) {

kfree(memory_buffer);

}

printk("<1>Removing memory module ");

}

int memory_open(struct inode *inode, struct file *filp) {

/* Success */

return 0;

}

int memory_release(struct inode *inode, struct file *filp) {

/* Success */

return 0;

}

ssize_t memory_read(struct file *filp, char *buf,

size_t count, loff_t *f_pos) {

/* Transfering data to user space */

copy_to_user(buf,memory_buffer,10);

/* Changing reading position as best suits */

if (*f_pos == 0) {

*f_pos+=1;

return 1;

} else {

return 0;

} }

ssize_t memory_write( struct file *filp, const char *buf,

size_t count, loff_t *f_pos) {

char *tmp; int chA=97, chZ=122; if(buf>= chA || buf<=122) //something goes here but im not figuring it out

tmp=...

copy_from_user(memory_buffer,tmp,10);

return 1;

}