Linux Kernel Notes-01

1.obj-y +=xxx.o This module is compiled to zImage

obj-m +=xxx.o The module will not be compiled to zImage, but a standalone xxx.ko will be generated statically compiled (modular)

2.scull driver (scull is a piece of memory in the kernel, not a specific device, generally used for testing)

Add the scull driver code to the drivers/char directory of the kernel source code (the purpose is to see the data structure of the kernel)

ls -l to see the device type, major device number and minor device number

cat /proc/devices to view the current major device number

3. Core data structure:

struct file_operations scull_fops = {
	.owner =    THIS_MODULE,
	.llseek =   scull_llseek,
	.read =     scull_read,
	.write =    scull_write,
	.ioctl =    scull_ioctl,
	.open =     scull_open,
	.release =  scull_release,
};

//struct scull_dev
struct scull_dev {
	struct scull_qset *data;  /* Pointer to first quantum set */
	int quantum;              /* the current quantum size */
	int qset;                 /* the current array size */
	unsigned long size;       /* amount of data stored here */
	unsigned int access_key;  /* used by sculluid and scullpriv */
	struct semaphore sem;     /* mutual exclusion semaphore     */
	struct cdev cdev;	  /* Char device structure*/
};

/*
 * NOTE:
 * read, write, poll, fsync, readv, writev, unlocked_ioctl and compat_ioctl
 * can be called without the big kernel lock held in all filesystems.
 */
struct file_operations {
	struct module *owner;
	loff_t (*llseek) (struct file *, loff_t, int);
	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
	ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
	ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
	int (*readdir) (struct file *, void *, filldir_t);
	unsigned int (*poll) (struct file *, struct poll_table_struct *);
	int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
	long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
	int (*mmap) (struct file *, struct vm_area_struct *);
	int (*open) (struct inode *, struct file *);
	int (*flush) (struct file *, fl_owner_t id);
	int (*release) (struct inode *, struct file *);
	int (*fsync) (struct file *, struct dentry *, int datasync);
	int (*aio_fsync) (struct kiocb *, int datasync);
	int (*fasync) (int, struct file *, int);
	int (*lock) (struct file *, int, struct file_lock *);
	ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
	int (*check_flags)(int);
	int (*flock) (struct file *, int, struct file_lock *);
	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
	ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
	int (*setlease)(struct file *, long, struct file_lock **);
};

struct cdev {
	struct kobject kobj;
	struct module *owner;
	const struct file_operations *ops;
	struct list_head list;
	dev_t dev;
	unsigned int count;
};