字符设备驱动程序

#ifndef _LINUX_CDEV_H
#define _LINUX_CDEV_H

#include <linux/kobject.h>
#include <linux/kdev_t.h>
#include <linux/list.h>

struct file_operations;
struct inode;
struct module;

struct cdev {
	struct kobject kobj;
	struct module *owner;
	const struct file_operations *ops;
	struct list_head list;
	dev_t dev;                       // 描述主设备和次设备号
	unsigned int count;
};

void cdev_init(struct cdev *, const struct file_operations *);

struct cdev *cdev_alloc(void);

void cdev_put(struct cdev *p);

int cdev_add(struct cdev *, dev_t, unsigned);

void cdev_del(struct cdev *);

void cd_forget(struct inode *);

#endif

static const struct file_operations tty_fops = {
        .llseek         = no_llseek,
        .read           = tty_read,
        .write          = tty_write,
        .poll           = tty_poll,
        .unlocked_ioctl = tty_ioctl,
        .compat_ioctl   = tty_compat_ioctl,
        .open           = tty_open,
        .release        = tty_release,
        .fasync         = tty_fasync,
};

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 (*read_iter) (struct kiocb *, struct iov_iter *);
	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
	int (*iterate) (struct file *, struct dir_context *);
	unsigned int (*poll) (struct file *, struct poll_table_struct *);
	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 *, loff_t, loff_t, 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 **, void **);
	long (*fallocate)(struct file *file, int mode, loff_t offset,
			  loff_t len);
	void (*show_fdinfo)(struct seq_file *m, struct file *f);
};

struct inode {

	union {
		struct pipe_inode_info	*i_pipe; // linux 内核管道
		struct block_device	*i_bdev; // 块设比
		struct cdev		*i_cdev; // 字符设备
		char			*i_link;
	};

}

struct file {
	union {
		struct llist_node	fu_llist;
		struct rcu_head 	fu_rcuhead;
	} f_u;
	struct path		f_path;                             // 文件路径
	struct inode		*f_inode;	/* cached value */  // 此文件相关的inode
	const struct file_operations	*f_op;                      // 可以在此文件上执行的操作

	/*
	 * Protects f_ep_links, f_flags.
	 * Must not be taken from IRQ context.
	 */
	spinlock_t		f_lock;
	atomic_long_t		f_count;
	unsigned int 		f_flags;
	fmode_t			f_mode;
	struct mutex		f_pos_lock;
	loff_t			f_pos;                             // 此文件中光标的位置
	struct fown_struct	f_owner;
	const struct cred	*f_cred;
	struct file_ra_state	f_ra;

	u64			f_version;
	/* needed for tty driver, and maybe others */
	void			*private_data;                     // 驱动程序可以设置的私有数据，以便在文件操作之间共享

static const struct file_operations tty_fops = {
	.llseek		= no_llseek,
	.read		= tty_read,
	.write		= tty_write,
	.poll		= tty_poll,
	.unlocked_ioctl	= tty_ioctl,
	.compat_ioctl	= tty_compat_ioctl,
	.open		= tty_open,
	.release	= tty_release,
	.fasync		= tty_fasync,
};

/*
 * Called by a tty driver to register itself.
 */
int tty_register_driver(struct tty_driver *driver)
{
	int error;
	int i;
	dev_t dev;
	struct device *d;

	if (!driver->major) {
		error = alloc_chrdev_region(&dev, driver->minor_start,
						driver->num, driver->name);
		if (!error) {
			driver->major = MAJOR(dev);
			driver->minor_start = MINOR(dev);
		}
	} else {
		dev = MKDEV(driver->major, driver->minor_start);
		error = register_chrdev_region(dev, driver->num, driver->name);
	}
	if (error < 0)
		goto err;

	if (driver->flags & TTY_DRIVER_DYNAMIC_ALLOC) {
		error = tty_cdev_add(driver, dev, 0, driver->num);
		if (error)
			goto err_unreg_char;
	}

	mutex_lock(&tty_mutex);
	list_add(&driver->tty_drivers, &tty_drivers);
	mutex_unlock(&tty_mutex);

	if (!(driver->flags & TTY_DRIVER_DYNAMIC_DEV)) {
		for (i = 0; i < driver->num; i++) {
			d = tty_register_device(driver, i, NULL);
			if (IS_ERR(d)) {
				error = PTR_ERR(d);
				goto err_unreg_devs;
			}
		}
	}
	proc_tty_register_driver(driver);
	driver->flags |= TTY_DRIVER_INSTALLED;
	return 0;

err_unreg_devs:
	for (i--; i >= 0; i--)
		tty_unregister_device(driver, i);

	mutex_lock(&tty_mutex);
	list_del(&driver->tty_drivers);
	mutex_unlock(&tty_mutex);

err_unreg_char:
	unregister_chrdev_region(dev, driver->num);
err:
	return error;
}
EXPORT_SYMBOL(tty_register_driver);

// 创建设备类，在sys/class中可见
static int __init tty_class_init(void)
{
	tty_class = class_create(THIS_MODULE, "tty");
	if (IS_ERR(tty_class))
		return PTR_ERR(tty_class);
	tty_class->devnode = tty_devnode;
	return 0;
}

postcore_initcall(tty_class_init);

/*
 * Ok, now we can initialize the rest of the tty devices and can count
 * on memory allocations, interrupts etc..
 */
int __init tty_init(void)
{
        //将file_operation绑定到cdev
	cdev_init(&tty_cdev, &tty_fops);

        //让用户访问设备
	if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||
	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)
		panic("Couldn't register /dev/tty driver\n");

	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL, "tty");

	cdev_init(&console_cdev, &console_fops);
	if (cdev_add(&console_cdev, MKDEV(TTYAUX_MAJOR, 1), 1) ||
	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 1), 1, "/dev/console") < 0)
		panic("Couldn't register /dev/console driver\n");
	consdev = device_create_with_groups(tty_class, NULL,
					    MKDEV(TTYAUX_MAJOR, 1), NULL,
					    cons_dev_groups, "console");
	if (IS_ERR(consdev))
		consdev = NULL;

#ifdef CONFIG_VT
	vty_init(&console_fops);
#endif
	return 0;
}

//*to是内核空间的指针，*from是用户空间指针，n表示从用户空间想内核空间拷贝数据的字节数
static inline long copy_from_user(void *to,
                const void __user * from, unsigned long n)
{
        unsigned long res = n;
        might_fault();
        if (likely(access_ok(VERIFY_READ, from, n)))
                res = __copy_from_user(to, from, n);
        if (unlikely(res))
                memset(to + (n - res), 0, res);
        return res;
}

static inline long copy_to_user(void __user *to,
                const void *from, unsigned long n)
{
        might_fault();
        if (access_ok(VERIFY_WRITE, to, n))
                return __copy_to_user(to, from, n);
        else
                return n;
}

static int tty_open(struct inode *inode, struct file *filp) {

	dev_t device = inode->i_rdev;

}

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

}

static ssize_t tty_write(struct file *file, const char __user *buf,
						size_t count, loff_t *ppos)
{
        //------------------------------------------------------
	/* Do the write .. */
	for (;;) {
		size_t size = count;
		if (size > chunk)
			size = chunk;
		ret = -EFAULT;
		if (copy_from_user(tty->write_buf, buf, size))
			break;
		ret = write(tty, file, tty->write_buf, size);
		if (ret <= 0)
			break;
		written += ret;
		buf += ret;
		count -= ret;
		if (!count)
			break;
		ret = -ERESTARTSYS;
		if (signal_pending(current))
			break;
		cond_resched();
	}
        //-------------------------------------------------------
}

static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
			loff_t *ppos)
{

    struct inode *inode = file_inode(file);

}

loff_t default_llseek(struct file *file, loff_t offset, int whence);

static unsigned int tty_poll(struct file *filp, poll_table *wait)

int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
{
	ktime_t expire, *to = NULL;
	struct poll_wqueues table;
	poll_table *wait;
	int retval, i, timed_out = 0;
	u64 slack = 0;
	unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
	unsigned long busy_end = 0;

	rcu_read_lock();
	retval = max_select_fd(n, fds);
	rcu_read_unlock();

	if (retval < 0)
		return retval;
	n = retval;

	poll_initwait(&table);
	wait = &table.pt;
	if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
		wait->_qproc = NULL;
		timed_out = 1;
	}

	if (end_time && !timed_out)
		slack = select_estimate_accuracy(end_time);

	retval = 0;
	for (;;) {
		unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
		bool can_busy_loop = false;

		inp = fds->in; outp = fds->out; exp = fds->ex;
		rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;

		for (i = 0; i < n; ++rinp, ++routp, ++rexp) {
			unsigned long in, out, ex, all_bits, bit = 1, mask, j;
			unsigned long res_in = 0, res_out = 0, res_ex = 0;

			in = *inp++; out = *outp++; ex = *exp++;
			all_bits = in | out | ex;
			if (all_bits == 0) {
				i += BITS_PER_LONG;
				continue;
			}

			for (j = 0; j < BITS_PER_LONG; ++j, ++i, bit <<= 1) {
				struct fd f;
				if (i >= n)
					break;
				if (!(bit & all_bits))
					continue;
				f = fdget(i);
				if (f.file) {
					const struct file_operations *f_op;
					f_op = f.file->f_op;
					mask = DEFAULT_POLLMASK;
					if (f_op->poll) {
						wait_key_set(wait, in, out,
							     bit, busy_flag);
						mask = (*f_op->poll)(f.file, wait);
					}
					fdput(f);
					if ((mask & POLLIN_SET) && (in & bit)) {
						res_in |= bit;
						retval++;
						wait->_qproc = NULL;
					}
					if ((mask & POLLOUT_SET) && (out & bit)) {
						res_out |= bit;
						retval++;
						wait->_qproc = NULL;
					}
					if ((mask & POLLEX_SET) && (ex & bit)) {
						res_ex |= bit;
						retval++;
						wait->_qproc = NULL;
					}
					/* got something, stop busy polling */
					if (retval) {
						can_busy_loop = false;
						busy_flag = 0;

					/*
					 * only remember a returned
					 * POLL_BUSY_LOOP if we asked for it
					 */
					} else if (busy_flag & mask)
						can_busy_loop = true;

				}
			}
			if (res_in)
				*rinp = res_in;
			if (res_out)
				*routp = res_out;
			if (res_ex)
				*rexp = res_ex;
			cond_resched();
		}
		wait->_qproc = NULL;

		if (retval || timed_out || signal_pending(current))
			break;
		if (table.error) {
			retval = table.error;
			break;
		}

		/* only if found POLL_BUSY_LOOP sockets && not out of time */
		if (can_busy_loop && !need_resched()) {
			if (!busy_end) {
				busy_end = busy_loop_end_time();
				continue;
			}
			if (!busy_loop_timeout(busy_end))
				continue;
		}
		busy_flag = 0;

		/*
		 * If this is the first loop and we have a timeout
		 * given, then we convert to ktime_t and set the to
		 * pointer to the expiry value.
		 */
		if (end_time && !to) {
			expire = timespec_to_ktime(*end_time);
			to = &expire;
		}

		if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
					   to, slack))
			timed_out = 1;
	}

	poll_freewait(&table);

	return retval;
}

/*
 * Split this up, as gcc can choke on it otherwise..
 */
long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	struct tty_struct *tty = file_tty(file);
	struct tty_struct *real_tty;
	void __user *p = (void __user *)arg;
	int retval;
	struct tty_ldisc *ld;

	if (tty_paranoia_check(tty, file_inode(file), "tty_ioctl"))
		return -EINVAL;

	real_tty = tty_pair_get_tty(tty);

	/*
	 * Factor out some common prep work
	 */
	switch (cmd) {
	case TIOCSETD:
	case TIOCSBRK:
	case TIOCCBRK:
	case TCSBRK:
	case TCSBRKP:
		retval = tty_check_change(tty);
		if (retval)
			return retval;
		if (cmd != TIOCCBRK) {
			tty_wait_until_sent(tty, 0);
			if (signal_pending(current))
				return -EINTR;
		}
		break;
	}

	/*
	 *	Now do the stuff.
	 */
	switch (cmd) {
	case TIOCSTI:
		return tiocsti(tty, p);
	case TIOCGWINSZ:
		return tiocgwinsz(real_tty, p);
	case TIOCSWINSZ:
		return tiocswinsz(real_tty, p);
	case TIOCCONS:
		return real_tty != tty ? -EINVAL : tioccons(file);
	case FIONBIO:
		return fionbio(file, p);
	case TIOCEXCL:
		set_bit(TTY_EXCLUSIVE, &tty->flags);
		return 0;
	case TIOCNXCL:
		clear_bit(TTY_EXCLUSIVE, &tty->flags);
		return 0;
	case TIOCGEXCL:
	{
		int excl = test_bit(TTY_EXCLUSIVE, &tty->flags);
		return put_user(excl, (int __user *)p);
	}
	case TIOCNOTTY:
		if (current->signal->tty != tty)
			return -ENOTTY;
		no_tty();
		return 0;
	case TIOCSCTTY:
		return tiocsctty(tty, file, arg);
	case TIOCGPGRP:
		return tiocgpgrp(tty, real_tty, p);
	case TIOCSPGRP:
		return tiocspgrp(tty, real_tty, p);
	case TIOCGSID:
		return tiocgsid(tty, real_tty, p);
	case TIOCGETD:
		return tiocgetd(tty, p);
	case TIOCSETD:
		return tiocsetd(tty, p);
	case TIOCVHANGUP:
		if (!capable(CAP_SYS_ADMIN))
			return -EPERM;
		tty_vhangup(tty);
		return 0;
	case TIOCGDEV:
	{
		unsigned int ret = new_encode_dev(tty_devnum(real_tty));
		return put_user(ret, (unsigned int __user *)p);
	}
	/*
	 * Break handling
	 */
	case TIOCSBRK:	/* Turn break on, unconditionally */
		if (tty->ops->break_ctl)
			return tty->ops->break_ctl(tty, -1);
		return 0;
	case TIOCCBRK:	/* Turn break off, unconditionally */
		if (tty->ops->break_ctl)
			return tty->ops->break_ctl(tty, 0);
		return 0;
	case TCSBRK:   /* SVID version: non-zero arg --> no break */
		/* non-zero arg means wait for all output data
		 * to be sent (performed above) but don't send break.
		 * This is used by the tcdrain() termios function.
		 */
		if (!arg)
			return send_break(tty, 250);
		return 0;
	case TCSBRKP:	/* support for POSIX tcsendbreak() */
		return send_break(tty, arg ? arg*100 : 250);

	case TIOCMGET:
		return tty_tiocmget(tty, p);
	case TIOCMSET:
	case TIOCMBIC:
	case TIOCMBIS:
		return tty_tiocmset(tty, cmd, p);
	case TIOCGICOUNT:
		retval = tty_tiocgicount(tty, p);
		/* For the moment allow fall through to the old method */
        	if (retval != -EINVAL)
			return retval;
		break;
	case TCFLSH:
		switch (arg) {
		case TCIFLUSH:
		case TCIOFLUSH:
		/* flush tty buffer and allow ldisc to process ioctl */
			tty_buffer_flush(tty, NULL);
			break;
		}
		break;
	case TIOCSSERIAL:
		tty_warn_deprecated_flags(p);
		break;
	}
	if (tty->ops->ioctl) {
		retval = tty->ops->ioctl(tty, cmd, arg);
		if (retval != -ENOIOCTLCMD)
			return retval;
	}
	ld = tty_ldisc_ref_wait(tty);
	retval = -EINVAL;
	if (ld->ops->ioctl) {
		retval = ld->ops->ioctl(tty, file, cmd, arg);
		if (retval == -ENOIOCTLCMD)
			retval = -ENOTTY;
	}
	tty_ldisc_deref(ld);
	return retval;
}