drivers/tty/vt/vc_screen.c - kernel/msm-4.19 - Gitiles

 /*
  * linux/drivers/char/vc_screen.c
  *
  * Provide access to virtual console memory.
  * /dev/vcs0: the screen as it is being viewed right now (possibly scrolled)
  * /dev/vcsN: the screen of /dev/ttyN (1 <= N <= 63)
  *            [minor: N]
  *
  * /dev/vcsaN: idem, but including attributes, and prefixed with
  *	the 4 bytes lines,columns,x,y (as screendump used to give).
  *	Attribute/character pair is in native endianity.
  *            [minor: N+128]
  *
  * This replaces screendump and part of selection, so that the system
  * administrator can control access using file system permissions.
  *
  * aeb@cwi.nl - efter Friedas begravelse - 950211
  *
  * machek@k332.feld.cvut.cz - modified not to send characters to wrong console
  *	 - fixed some fatal off-by-one bugs (0-- no longer == -1 -> looping and looping and looping...)
  *	 - making it shorter - scr_readw are macros which expand in PRETTY long code
  */

 #include <linux/kernel.h>
 #include <linux/major.h>
 #include <linux/errno.h>
 #include <linux/tty.h>
 #include <linux/interrupt.h>
 #include <linux/mm.h>
 #include <linux/init.h>
 #include <linux/vt_kern.h>
 #include <linux/selection.h>
 #include <linux/kbd_kern.h>
 #include <linux/console.h>
 #include <linux/device.h>
 #include <linux/smp_lock.h>
 #include <linux/sched.h>
 #include <linux/fs.h>
 #include <linux/poll.h>
 #include <linux/signal.h>
 #include <linux/slab.h>
 #include <linux/notifier.h>

 #include <asm/uaccess.h>
 #include <asm/byteorder.h>
 #include <asm/unaligned.h>

 #undef attr
 #undef org
 #undef addr
 #define HEADER_SIZE	4

 #define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 256 : PAGE_SIZE)

 struct vcs_poll_data {
 	struct notifier_block notifier;
 	unsigned int cons_num;
 	bool seen_last_update;
 	wait_queue_head_t waitq;
 	struct fasync_struct *fasync;
 };

 static int
 vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
 {
 	struct vt_notifier_param *param = _param;
 	struct vc_data *vc = param->vc;
 	struct vcs_poll_data *poll =
 		container_of(nb, struct vcs_poll_data, notifier);
 	int currcons = poll->cons_num;

 	if (code != VT_UPDATE)
 		return NOTIFY_DONE;

 	if (currcons == 0)
 		currcons = fg_console;
 	else
 		currcons--;
 	if (currcons != vc->vc_num)
 		return NOTIFY_DONE;

 	poll->seen_last_update = false;
 	wake_up_interruptible(&poll->waitq);
 	kill_fasync(&poll->fasync, SIGIO, POLL_IN);
 	return NOTIFY_OK;
 }

 static void
 vcs_poll_data_free(struct vcs_poll_data *poll)
 {
 	unregister_vt_notifier(&poll->notifier);
 	kfree(poll);
 }

 static struct vcs_poll_data *
 vcs_poll_data_get(struct file *file)
 {
 	struct vcs_poll_data *poll = file->private_data;

 	if (poll)
 		return poll;

 	poll = kzalloc(sizeof(*poll), GFP_KERNEL);
 	if (!poll)
 		return NULL;
 	poll->cons_num = iminor(file->f_path.dentry->d_inode) & 127;
 	init_waitqueue_head(&poll->waitq);
 	poll->notifier.notifier_call = vcs_notifier;
 	if (register_vt_notifier(&poll->notifier) != 0) {
 		kfree(poll);
 		return NULL;
 	}

 	/*
 	 * This code may be called either through ->poll() or ->fasync().
 	 * If we have two threads using the same file descriptor, they could
 	 * both enter this function, both notice that the structure hasn't
 	 * been allocated yet and go ahead allocating it in parallel, but
 	 * only one of them must survive and be shared otherwise we'd leak
 	 * memory with a dangling notifier callback.
 	 */
 	spin_lock(&file->f_lock);
 	if (!file->private_data) {
 		file->private_data = poll;
 	} else {
 		/* someone else raced ahead of us */
 		vcs_poll_data_free(poll);
 		poll = file->private_data;
 	}
 	spin_unlock(&file->f_lock);

 	return poll;
 }

 /*
  * Returns VC for inode.
  * Must be called with console_lock.
  */
 static struct vc_data*
 vcs_vc(struct inode *inode, int *viewed)
 {
 	unsigned int currcons = iminor(inode) & 127;

 	WARN_CONSOLE_UNLOCKED();

 	if (currcons == 0) {
 		currcons = fg_console;
 		if (viewed)
 			*viewed = 1;
 	} else {
 		currcons--;
 		if (viewed)
 			*viewed = 0;
 	}
 	return vc_cons[currcons].d;
 }

 /*
  * Returns size for VC carried by inode.
  * Must be called with console_lock.
  */
 static int
 vcs_size(struct inode *inode)
 {
 	int size;
 	int minor = iminor(inode);
 	struct vc_data *vc;

 	WARN_CONSOLE_UNLOCKED();

 	vc = vcs_vc(inode, NULL);
 	if (!vc)
 		return -ENXIO;

 	size = vc->vc_rows * vc->vc_cols;

 	if (minor & 128)
 		size = 2*size + HEADER_SIZE;
 	return size;
 }

 static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
 {
 	int size;

 	console_lock();
 	size = vcs_size(file->f_path.dentry->d_inode);
 	console_unlock();
 	if (size < 0)
 		return size;
 	switch (orig) {
 		default:
 			return -EINVAL;
 		case 2:
 			offset += size;
 			break;
 		case 1:
 			offset += file->f_pos;
 		case 0:
 			break;
 	}
 	if (offset < 0 || offset > size) {
 		return -EINVAL;
 	}
 	file->f_pos = offset;
 	return file->f_pos;
 }


 static ssize_t
 vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
 	unsigned int currcons = iminor(inode);
 	struct vc_data *vc;
 	struct vcs_poll_data *poll;
 	long pos;
 	long attr, read;
 	int col, maxcol, viewed;
 	unsigned short *org = NULL;
 	ssize_t ret;
 	char *con_buf;

 	con_buf = (char *) __get_free_page(GFP_KERNEL);
 	if (!con_buf)
 		return -ENOMEM;

 	pos = *ppos;

 	/* Select the proper current console and verify
 	 * sanity of the situation under the console lock.
 	 */
 	console_lock();

 	attr = (currcons & 128);
 	ret = -ENXIO;
 	vc = vcs_vc(inode, &viewed);
 	if (!vc)
 		goto unlock_out;

 	ret = -EINVAL;
 	if (pos < 0)
 		goto unlock_out;
 	poll = file->private_data;
 	if (count && poll)
 		poll->seen_last_update = true;
 	read = 0;
 	ret = 0;
 	while (count) {
 		char *con_buf0, *con_buf_start;
 		long this_round, size;
 		ssize_t orig_count;
 		long p = pos;

 		/* Check whether we are above size each round,
 		 * as copy_to_user at the end of this loop
 		 * could sleep.
 		 */
 		size = vcs_size(inode);
 		if (size < 0) {
 			if (read)
 				break;
 			ret = size;
 			goto unlock_out;
 		}
 		if (pos >= size)
 			break;
 		if (count > size - pos)
 			count = size - pos;

 		this_round = count;
 		if (this_round > CON_BUF_SIZE)
 			this_round = CON_BUF_SIZE;

 		/* Perform the whole read into the local con_buf.
 		 * Then we can drop the console spinlock and safely
 		 * attempt to move it to userspace.
 		 */

 		con_buf_start = con_buf0 = con_buf;
 		orig_count = this_round;
 		maxcol = vc->vc_cols;
 		if (!attr) {
 			org = screen_pos(vc, p, viewed);
 			col = p % maxcol;
 			p += maxcol - col;
 			while (this_round-- > 0) {
 				*con_buf0++ = (vcs_scr_readw(vc, org++) & 0xff);
 				if (++col == maxcol) {
 					org = screen_pos(vc, p, viewed);
 					col = 0;
 					p += maxcol;
 				}
 			}
 		} else {
 			if (p < HEADER_SIZE) {
 				size_t tmp_count;

 				con_buf0[0] = (char)vc->vc_rows;
 				con_buf0[1] = (char)vc->vc_cols;
 				getconsxy(vc, con_buf0 + 2);

 				con_buf_start += p;
 				this_round += p;
 				if (this_round > CON_BUF_SIZE) {
 					this_round = CON_BUF_SIZE;
 					orig_count = this_round - p;
 				}

 				tmp_count = HEADER_SIZE;
 				if (tmp_count > this_round)
 					tmp_count = this_round;

 				/* Advance state pointers and move on. */
 				this_round -= tmp_count;
 				p = HEADER_SIZE;
 				con_buf0 = con_buf + HEADER_SIZE;
 				/* If this_round >= 0, then p is even... */
 			} else if (p & 1) {
 				/* Skip first byte for output if start address is odd
 				 * Update region sizes up/down depending on free
 				 * space in buffer.
 				 */
 				con_buf_start++;
 				if (this_round < CON_BUF_SIZE)
 					this_round++;
 				else
 					orig_count--;
 			}
 			if (this_round > 0) {
 				unsigned short *tmp_buf = (unsigned short *)con_buf0;

 				p -= HEADER_SIZE;
 				p /= 2;
 				col = p % maxcol;

 				org = screen_pos(vc, p, viewed);
 				p += maxcol - col;

 				/* Buffer has even length, so we can always copy
 				 * character + attribute. We do not copy last byte
 				 * to userspace if this_round is odd.
 				 */
 				this_round = (this_round + 1) >> 1;

 				while (this_round) {
 					*tmp_buf++ = vcs_scr_readw(vc, org++);
 					this_round --;
 					if (++col == maxcol) {
 						org = screen_pos(vc, p, viewed);
 						col = 0;
 						p += maxcol;
 					}
 				}
 			}
 		}

 		/* Finally, release the console semaphore while we push
 		 * all the data to userspace from our temporary buffer.
 		 *
 		 * AKPM: Even though it's a semaphore, we should drop it because
 		 * the pagefault handling code may want to call printk().
 		 */

 		console_unlock();
 		ret = copy_to_user(buf, con_buf_start, orig_count);
 		console_lock();

 		if (ret) {
 			read += (orig_count - ret);
 			ret = -EFAULT;
 			break;
 		}
 		buf += orig_count;
 		pos += orig_count;
 		read += orig_count;
 		count -= orig_count;
 	}
 	*ppos += read;
 	if (read)
 		ret = read;
 unlock_out:
 	console_unlock();
 	free_page((unsigned long) con_buf);
 	return ret;
 }

 static ssize_t
 vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
 	unsigned int currcons = iminor(inode);
 	struct vc_data *vc;
 	long pos;
 	long attr, size, written;
 	char *con_buf0;
 	int col, maxcol, viewed;
 	u16 *org0 = NULL, *org = NULL;
 	size_t ret;
 	char *con_buf;

 	con_buf = (char *) __get_free_page(GFP_KERNEL);
 	if (!con_buf)
 		return -ENOMEM;

 	pos = *ppos;

 	/* Select the proper current console and verify
 	 * sanity of the situation under the console lock.
 	 */
 	console_lock();

 	attr = (currcons & 128);
 	ret = -ENXIO;
 	vc = vcs_vc(inode, &viewed);
 	if (!vc)
 		goto unlock_out;

 	size = vcs_size(inode);
 	ret = -EINVAL;
 	if (pos < 0 || pos > size)
 		goto unlock_out;
 	if (count > size - pos)
 		count = size - pos;
 	written = 0;
 	while (count) {
 		long this_round = count;
 		size_t orig_count;
 		long p;

 		if (this_round > CON_BUF_SIZE)
 			this_round = CON_BUF_SIZE;

 		/* Temporarily drop the console lock so that we can read
 		 * in the write data from userspace safely.
 		 */
 		console_unlock();
 		ret = copy_from_user(con_buf, buf, this_round);
 		console_lock();

 		if (ret) {
 			this_round -= ret;
 			if (!this_round) {
 				/* Abort loop if no data were copied. Otherwise
 				 * fail with -EFAULT.
 				 */
 				if (written)
 					break;
 				ret = -EFAULT;
 				goto unlock_out;
 			}
 		}

 		/* The vcs_size might have changed while we slept to grab
 		 * the user buffer, so recheck.
 		 * Return data written up to now on failure.
 		 */
 		size = vcs_size(inode);
 		if (size < 0) {
 			if (written)
 				break;
 			ret = size;
 			goto unlock_out;
 		}
 		if (pos >= size)
 			break;
 		if (this_round > size - pos)
 			this_round = size - pos;

 		/* OK, now actually push the write to the console
 		 * under the lock using the local kernel buffer.
 		 */

 		con_buf0 = con_buf;
 		orig_count = this_round;
 		maxcol = vc->vc_cols;
 		p = pos;
 		if (!attr) {
 			org0 = org = screen_pos(vc, p, viewed);
 			col = p % maxcol;
 			p += maxcol - col;

 			while (this_round > 0) {
 				unsigned char c = *con_buf0++;

 				this_round--;
 				vcs_scr_writew(vc,
 					       (vcs_scr_readw(vc, org) & 0xff00) | c, org);
 				org++;
 				if (++col == maxcol) {
 					org = screen_pos(vc, p, viewed);
 					col = 0;
 					p += maxcol;
 				}
 			}
 		} else {
 			if (p < HEADER_SIZE) {
 				char header[HEADER_SIZE];

 				getconsxy(vc, header + 2);
 				while (p < HEADER_SIZE && this_round > 0) {
 					this_round--;
 					header[p++] = *con_buf0++;
 				}
 				if (!viewed)
 					putconsxy(vc, header + 2);
 			}
 			p -= HEADER_SIZE;
 			col = (p/2) % maxcol;
 			if (this_round > 0) {
 				org0 = org = screen_pos(vc, p/2, viewed);
 				if ((p & 1) && this_round > 0) {
 					char c;

 					this_round--;
 					c = *con_buf0++;
 #ifdef __BIG_ENDIAN
 					vcs_scr_writew(vc, c |
 					     (vcs_scr_readw(vc, org) & 0xff00), org);
 #else
 					vcs_scr_writew(vc, (c << 8) |
 					     (vcs_scr_readw(vc, org) & 0xff), org);
 #endif
 					org++;
 					p++;
 					if (++col == maxcol) {
 						org = screen_pos(vc, p/2, viewed);
 						col = 0;
 					}
 				}
 				p /= 2;
 				p += maxcol - col;
 			}
 			while (this_round > 1) {
 				unsigned short w;

 				w = get_unaligned(((unsigned short *)con_buf0));
 				vcs_scr_writew(vc, w, org++);
 				con_buf0 += 2;
 				this_round -= 2;
 				if (++col == maxcol) {
 					org = screen_pos(vc, p, viewed);
 					col = 0;
 					p += maxcol;
 				}
 			}
 			if (this_round > 0) {
 				unsigned char c;

 				c = *con_buf0++;
 #ifdef __BIG_ENDIAN
 				vcs_scr_writew(vc, (vcs_scr_readw(vc, org) & 0xff) | (c << 8), org);
 #else
 				vcs_scr_writew(vc, (vcs_scr_readw(vc, org) & 0xff00) | c, org);
 #endif
 			}
 		}
 		count -= orig_count;
 		written += orig_count;
 		buf += orig_count;
 		pos += orig_count;
 		if (org0)
 			update_region(vc, (unsigned long)(org0), org - org0);
 	}
 	*ppos += written;
 	ret = written;
 	if (written)
 		vcs_scr_updated(vc);

 unlock_out:
 	console_unlock();
 	free_page((unsigned long) con_buf);
 	return ret;
 }

 static unsigned int
 vcs_poll(struct file *file, poll_table *wait)
 {
 	struct vcs_poll_data *poll = vcs_poll_data_get(file);
 	int ret = DEFAULT_POLLMASK|POLLERR|POLLPRI;

 	if (poll) {
 		poll_wait(file, &poll->waitq, wait);
 		if (poll->seen_last_update)
 			ret = DEFAULT_POLLMASK;
 	}
 	return ret;
 }

 static int
 vcs_fasync(int fd, struct file *file, int on)
 {
 	struct vcs_poll_data *poll = file->private_data;

 	if (!poll) {
 		/* don't allocate anything if all we want is disable fasync */
 		if (!on)
 			return 0;
 		poll = vcs_poll_data_get(file);
 		if (!poll)
 			return -ENOMEM;
 	}

 	return fasync_helper(fd, file, on, &poll->fasync);
 }

 static int
 vcs_open(struct inode *inode, struct file *filp)
 {
 	unsigned int currcons = iminor(inode) & 127;
 	int ret = 0;

 	tty_lock();
 	if(currcons && !vc_cons_allocated(currcons-1))
 		ret = -ENXIO;
 	tty_unlock();
 	return ret;
 }

 static int vcs_release(struct inode *inode, struct file *file)
 {
 	struct vcs_poll_data *poll = file->private_data;

 	if (poll)
 		vcs_poll_data_free(poll);
 	return 0;
 }

 static const struct file_operations vcs_fops = {
 	.llseek		= vcs_lseek,
 	.read		= vcs_read,
 	.write		= vcs_write,
 	.poll		= vcs_poll,
 	.fasync		= vcs_fasync,
 	.open		= vcs_open,
 	.release	= vcs_release,
 };

 static struct class *vc_class;

 void vcs_make_sysfs(int index)
 {
 	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL,
 		      "vcs%u", index + 1);
 	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL,
 		      "vcsa%u", index + 1);
 }

 void vcs_remove_sysfs(int index)
 {
 	device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 1));
 	device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 129));
 }

 int __init vcs_init(void)
 {
 	unsigned int i;

 	if (register_chrdev(VCS_MAJOR, "vcs", &vcs_fops))
 		panic("unable to get major %d for vcs device", VCS_MAJOR);
 	vc_class = class_create(THIS_MODULE, "vc");

 	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 0), NULL, "vcs");
 	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 128), NULL, "vcsa");
 	for (i = 0; i < MIN_NR_CONSOLES; i++)
 		vcs_make_sysfs(i);
 	return 0;
 }
	/*
	* linux/drivers/char/vc_screen.c
	*
	* Provide access to virtual console memory.
	* /dev/vcs0: the screen as it is being viewed right now (possibly scrolled)
	* /dev/vcsN: the screen of /dev/ttyN (1 <= N <= 63)
	* [minor: N]
	*
	* /dev/vcsaN: idem, but including attributes, and prefixed with
	* the 4 bytes lines,columns,x,y (as screendump used to give).
	* Attribute/character pair is in native endianity.
	* [minor: N+128]
	*
	* This replaces screendump and part of selection, so that the system
	* administrator can control access using file system permissions.
	*
	* aeb@cwi.nl - efter Friedas begravelse - 950211
	*
	* machek@k332.feld.cvut.cz - modified not to send characters to wrong console
	* - fixed some fatal off-by-one bugs (0-- no longer == -1 -> looping and looping and looping...)
	* - making it shorter - scr_readw are macros which expand in PRETTY long code
	*/

	#include <linux/kernel.h>
	#include <linux/major.h>
	#include <linux/errno.h>
	#include <linux/tty.h>
	#include <linux/interrupt.h>
	#include <linux/mm.h>
	#include <linux/init.h>
	#include <linux/vt_kern.h>
	#include <linux/selection.h>
	#include <linux/kbd_kern.h>
	#include <linux/console.h>
	#include <linux/device.h>
	#include <linux/smp_lock.h>
	#include <linux/sched.h>
	#include <linux/fs.h>
	#include <linux/poll.h>
	#include <linux/signal.h>
	#include <linux/slab.h>
	#include <linux/notifier.h>

	#include <asm/uaccess.h>
	#include <asm/byteorder.h>
	#include <asm/unaligned.h>

	#undef attr
	#undef org
	#undef addr
	#define HEADER_SIZE 4

	#define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 256 : PAGE_SIZE)

	struct vcs_poll_data {
	struct notifier_block notifier;
	unsigned int cons_num;
	bool seen_last_update;
	wait_queue_head_t waitq;
	struct fasync_struct *fasync;
	};

	static int
	vcs_notifier(struct notifier_block nb, unsigned long code, void _param)
	{
	struct vt_notifier_param *param = _param;
	struct vc_data *vc = param->vc;
	struct vcs_poll_data *poll =
	container_of(nb, struct vcs_poll_data, notifier);
	int currcons = poll->cons_num;

	if (code != VT_UPDATE)
	return NOTIFY_DONE;

	if (currcons == 0)
	currcons = fg_console;
	else
	currcons--;
	if (currcons != vc->vc_num)
	return NOTIFY_DONE;

	poll->seen_last_update = false;
	wake_up_interruptible(&poll->waitq);
	kill_fasync(&poll->fasync, SIGIO, POLL_IN);
	return NOTIFY_OK;
	}

	static void
	vcs_poll_data_free(struct vcs_poll_data *poll)
	{
	unregister_vt_notifier(&poll->notifier);
	kfree(poll);
	}

	static struct vcs_poll_data *
	vcs_poll_data_get(struct file *file)
	{
	struct vcs_poll_data *poll = file->private_data;

	if (poll)
	return poll;

	poll = kzalloc(sizeof(*poll), GFP_KERNEL);
	if (!poll)
	return NULL;
	poll->cons_num = iminor(file->f_path.dentry->d_inode) & 127;
	init_waitqueue_head(&poll->waitq);
	poll->notifier.notifier_call = vcs_notifier;
	if (register_vt_notifier(&poll->notifier) != 0) {
	kfree(poll);
	return NULL;
	}

	/*
	* This code may be called either through ->poll() or ->fasync().
	* If we have two threads using the same file descriptor, they could
	* both enter this function, both notice that the structure hasn't
	* been allocated yet and go ahead allocating it in parallel, but
	* only one of them must survive and be shared otherwise we'd leak
	* memory with a dangling notifier callback.
	*/
	spin_lock(&file->f_lock);
	if (!file->private_data) {
	file->private_data = poll;
	} else {
	/* someone else raced ahead of us */
	vcs_poll_data_free(poll);
	poll = file->private_data;
	}
	spin_unlock(&file->f_lock);

	return poll;
	}

	/*
	* Returns VC for inode.
	* Must be called with console_lock.
	*/
	static struct vc_data*
	vcs_vc(struct inode inode, int viewed)
	{
	unsigned int currcons = iminor(inode) & 127;

	WARN_CONSOLE_UNLOCKED();

	if (currcons == 0) {
	currcons = fg_console;
	if (viewed)
	*viewed = 1;
	} else {
	currcons--;
	if (viewed)
	*viewed = 0;
	}
	return vc_cons[currcons].d;
	}

	/*
	* Returns size for VC carried by inode.
	* Must be called with console_lock.
	*/
	static int
	vcs_size(struct inode *inode)
	{
	int size;
	int minor = iminor(inode);
	struct vc_data *vc;

	WARN_CONSOLE_UNLOCKED();

	vc = vcs_vc(inode, NULL);
	if (!vc)
	return -ENXIO;

	size = vc->vc_rows * vc->vc_cols;

	if (minor & 128)
	size = 2*size + HEADER_SIZE;
	return size;
	}

	static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
	{
	int size;

	console_lock();
	size = vcs_size(file->f_path.dentry->d_inode);
	console_unlock();
	if (size < 0)
	return size;
	switch (orig) {
	default:
	return -EINVAL;
	case 2:
	offset += size;
	break;
	case 1:
	offset += file->f_pos;
	case 0:
	break;
	}
	if (offset < 0 \|\| offset > size) {
	return -EINVAL;
	}
	file->f_pos = offset;
	return file->f_pos;
	}


	static ssize_t
	vcs_read(struct file file, char __user buf, size_t count, loff_t *ppos)
	{
	struct inode *inode = file->f_path.dentry->d_inode;
	unsigned int currcons = iminor(inode);
	struct vc_data *vc;
	struct vcs_poll_data *poll;
	long pos;
	long attr, read;
	int col, maxcol, viewed;
	unsigned short *org = NULL;
	ssize_t ret;
	char *con_buf;

	con_buf = (char *) __get_free_page(GFP_KERNEL);
	if (!con_buf)
	return -ENOMEM;

	pos = *ppos;

	/* Select the proper current console and verify
	* sanity of the situation under the console lock.
	*/
	console_lock();

	attr = (currcons & 128);
	ret = -ENXIO;
	vc = vcs_vc(inode, &viewed);
	if (!vc)
	goto unlock_out;

	ret = -EINVAL;
	if (pos < 0)
	goto unlock_out;
	poll = file->private_data;
	if (count && poll)
	poll->seen_last_update = true;
	read = 0;
	ret = 0;
	while (count) {
	char con_buf0, con_buf_start;
	long this_round, size;
	ssize_t orig_count;
	long p = pos;

	/* Check whether we are above size each round,
	* as copy_to_user at the end of this loop
	* could sleep.
	*/
	size = vcs_size(inode);
	if (size < 0) {
	if (read)
	break;
	ret = size;
	goto unlock_out;
	}
	if (pos >= size)
	break;
	if (count > size - pos)
	count = size - pos;

	this_round = count;
	if (this_round > CON_BUF_SIZE)
	this_round = CON_BUF_SIZE;

	/* Perform the whole read into the local con_buf.
	* Then we can drop the console spinlock and safely
	* attempt to move it to userspace.
	*/

	con_buf_start = con_buf0 = con_buf;
	orig_count = this_round;
	maxcol = vc->vc_cols;
	if (!attr) {
	org = screen_pos(vc, p, viewed);
	col = p % maxcol;
	p += maxcol - col;
	while (this_round-- > 0) {
	*con_buf0++ = (vcs_scr_readw(vc, org++) & 0xff);
	if (++col == maxcol) {
	org = screen_pos(vc, p, viewed);
	col = 0;
	p += maxcol;
	}
	}
	} else {
	if (p < HEADER_SIZE) {
	size_t tmp_count;

	con_buf0[0] = (char)vc->vc_rows;
	con_buf0[1] = (char)vc->vc_cols;
	getconsxy(vc, con_buf0 + 2);

	con_buf_start += p;
	this_round += p;
	if (this_round > CON_BUF_SIZE) {
	this_round = CON_BUF_SIZE;
	orig_count = this_round - p;
	}

	tmp_count = HEADER_SIZE;
	if (tmp_count > this_round)
	tmp_count = this_round;

	/* Advance state pointers and move on. */
	this_round -= tmp_count;
	p = HEADER_SIZE;
	con_buf0 = con_buf + HEADER_SIZE;
	/* If this_round >= 0, then p is even... */
	} else if (p & 1) {
	/* Skip first byte for output if start address is odd
	* Update region sizes up/down depending on free
	* space in buffer.
	*/
	con_buf_start++;
	if (this_round < CON_BUF_SIZE)
	this_round++;
	else
	orig_count--;
	}
	if (this_round > 0) {
	unsigned short tmp_buf = (unsigned short )con_buf0;

	p -= HEADER_SIZE;
	p /= 2;
	col = p % maxcol;

	org = screen_pos(vc, p, viewed);
	p += maxcol - col;

	/* Buffer has even length, so we can always copy
	* character + attribute. We do not copy last byte
	* to userspace if this_round is odd.
	*/
	this_round = (this_round + 1) >> 1;

	while (this_round) {
	*tmp_buf++ = vcs_scr_readw(vc, org++);
	this_round --;
	if (++col == maxcol) {
	org = screen_pos(vc, p, viewed);
	col = 0;
	p += maxcol;
	}
	}
	}
	}

	/* Finally, release the console semaphore while we push
	* all the data to userspace from our temporary buffer.
	*
	* AKPM: Even though it's a semaphore, we should drop it because
	* the pagefault handling code may want to call printk().
	*/

	console_unlock();
	ret = copy_to_user(buf, con_buf_start, orig_count);
	console_lock();

	if (ret) {
	read += (orig_count - ret);
	ret = -EFAULT;
	break;
	}
	buf += orig_count;
	pos += orig_count;
	read += orig_count;
	count -= orig_count;
	}
	*ppos += read;
	if (read)
	ret = read;
	unlock_out:
	console_unlock();
	free_page((unsigned long) con_buf);
	return ret;
	}

	static ssize_t
	vcs_write(struct file file, const char __user buf, size_t count, loff_t *ppos)
	{
	struct inode *inode = file->f_path.dentry->d_inode;
	unsigned int currcons = iminor(inode);
	struct vc_data *vc;
	long pos;
	long attr, size, written;
	char *con_buf0;
	int col, maxcol, viewed;
	u16 org0 = NULL, org = NULL;
	size_t ret;
	char *con_buf;

	con_buf = (char *) __get_free_page(GFP_KERNEL);
	if (!con_buf)
	return -ENOMEM;

	pos = *ppos;

	/* Select the proper current console and verify
	* sanity of the situation under the console lock.
	*/
	console_lock();

	attr = (currcons & 128);
	ret = -ENXIO;
	vc = vcs_vc(inode, &viewed);
	if (!vc)
	goto unlock_out;

	size = vcs_size(inode);
	ret = -EINVAL;
	if (pos < 0 \|\| pos > size)
	goto unlock_out;
	if (count > size - pos)
	count = size - pos;
	written = 0;
	while (count) {
	long this_round = count;
	size_t orig_count;
	long p;

	if (this_round > CON_BUF_SIZE)
	this_round = CON_BUF_SIZE;

	/* Temporarily drop the console lock so that we can read
	* in the write data from userspace safely.
	*/
	console_unlock();
	ret = copy_from_user(con_buf, buf, this_round);
	console_lock();

	if (ret) {
	this_round -= ret;
	if (!this_round) {
	/* Abort loop if no data were copied. Otherwise
	* fail with -EFAULT.
	*/
	if (written)
	break;
	ret = -EFAULT;
	goto unlock_out;
	}
	}

	/* The vcs_size might have changed while we slept to grab
	* the user buffer, so recheck.
	* Return data written up to now on failure.
	*/
	size = vcs_size(inode);
	if (size < 0) {
	if (written)
	break;
	ret = size;
	goto unlock_out;
	}
	if (pos >= size)
	break;
	if (this_round > size - pos)
	this_round = size - pos;

	/* OK, now actually push the write to the console
	* under the lock using the local kernel buffer.
	*/

	con_buf0 = con_buf;
	orig_count = this_round;
	maxcol = vc->vc_cols;
	p = pos;
	if (!attr) {
	org0 = org = screen_pos(vc, p, viewed);
	col = p % maxcol;
	p += maxcol - col;

	while (this_round > 0) {
	unsigned char c = *con_buf0++;

	this_round--;
	vcs_scr_writew(vc,
	(vcs_scr_readw(vc, org) & 0xff00) \| c, org);
	org++;
	if (++col == maxcol) {
	org = screen_pos(vc, p, viewed);
	col = 0;
	p += maxcol;
	}
	}
	} else {
	if (p < HEADER_SIZE) {
	char header[HEADER_SIZE];

	getconsxy(vc, header + 2);
	while (p < HEADER_SIZE && this_round > 0) {
	this_round--;
	header[p++] = *con_buf0++;
	}
	if (!viewed)
	putconsxy(vc, header + 2);
	}
	p -= HEADER_SIZE;
	col = (p/2) % maxcol;
	if (this_round > 0) {
	org0 = org = screen_pos(vc, p/2, viewed);
	if ((p & 1) && this_round > 0) {
	char c;

	this_round--;
	c = *con_buf0++;
	#ifdef __BIG_ENDIAN
	vcs_scr_writew(vc, c \|
	(vcs_scr_readw(vc, org) & 0xff00), org);
	#else
	vcs_scr_writew(vc, (c << 8) \|
	(vcs_scr_readw(vc, org) & 0xff), org);
	#endif
	org++;
	p++;
	if (++col == maxcol) {
	org = screen_pos(vc, p/2, viewed);
	col = 0;
	}
	}
	p /= 2;
	p += maxcol - col;
	}
	while (this_round > 1) {
	unsigned short w;

	w = get_unaligned(((unsigned short *)con_buf0));
	vcs_scr_writew(vc, w, org++);
	con_buf0 += 2;
	this_round -= 2;
	if (++col == maxcol) {
	org = screen_pos(vc, p, viewed);
	col = 0;
	p += maxcol;
	}
	}
	if (this_round > 0) {
	unsigned char c;

	c = *con_buf0++;
	#ifdef __BIG_ENDIAN
	vcs_scr_writew(vc, (vcs_scr_readw(vc, org) & 0xff) \| (c << 8), org);
	#else
	vcs_scr_writew(vc, (vcs_scr_readw(vc, org) & 0xff00) \| c, org);
	#endif
	}
	}
	count -= orig_count;
	written += orig_count;
	buf += orig_count;
	pos += orig_count;
	if (org0)
	update_region(vc, (unsigned long)(org0), org - org0);
	}
	*ppos += written;
	ret = written;
	if (written)
	vcs_scr_updated(vc);

	unlock_out:
	console_unlock();
	free_page((unsigned long) con_buf);
	return ret;
	}

	static unsigned int
	vcs_poll(struct file file, poll_table wait)
	{
	struct vcs_poll_data *poll = vcs_poll_data_get(file);
	int ret = DEFAULT_POLLMASK\|POLLERR\|POLLPRI;

	if (poll) {
	poll_wait(file, &poll->waitq, wait);
	if (poll->seen_last_update)
	ret = DEFAULT_POLLMASK;
	}
	return ret;
	}

	static int
	vcs_fasync(int fd, struct file *file, int on)
	{
	struct vcs_poll_data *poll = file->private_data;

	if (!poll) {
	/* don't allocate anything if all we want is disable fasync */
	if (!on)
	return 0;
	poll = vcs_poll_data_get(file);
	if (!poll)
	return -ENOMEM;
	}

	return fasync_helper(fd, file, on, &poll->fasync);
	}

	static int
	vcs_open(struct inode inode, struct file filp)
	{
	unsigned int currcons = iminor(inode) & 127;
	int ret = 0;

	tty_lock();
	if(currcons && !vc_cons_allocated(currcons-1))
	ret = -ENXIO;
	tty_unlock();
	return ret;
	}

	static int vcs_release(struct inode inode, struct file file)
	{
	struct vcs_poll_data *poll = file->private_data;

	if (poll)
	vcs_poll_data_free(poll);
	return 0;
	}

	static const struct file_operations vcs_fops = {
	.llseek = vcs_lseek,
	.read = vcs_read,
	.write = vcs_write,
	.poll = vcs_poll,
	.fasync = vcs_fasync,
	.open = vcs_open,
	.release = vcs_release,
	};

	static struct class *vc_class;

	void vcs_make_sysfs(int index)
	{
	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL,
	"vcs%u", index + 1);
	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL,
	"vcsa%u", index + 1);
	}

	void vcs_remove_sysfs(int index)
	{
	device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 1));
	device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 129));
	}

	int __init vcs_init(void)
	{
	unsigned int i;

	if (register_chrdev(VCS_MAJOR, "vcs", &vcs_fops))
	panic("unable to get major %d for vcs device", VCS_MAJOR);
	vc_class = class_create(THIS_MODULE, "vc");

	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 0), NULL, "vcs");
	device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 128), NULL, "vcsa");
	for (i = 0; i < MIN_NR_CONSOLES; i++)
	vcs_make_sysfs(i);
	return 0;
	}