vc_screen.c
// SPDX-License-Identifier: GPL-2.0
/*
* Provide access to virtual console memory.
* /dev/vcs: 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]
*
* /dev/vcsuN: similar to /dev/vcsaN but using 4-byte unicode values
* instead of 1-byte screen glyph values.
* [minor: N+64]
*
* /dev/vcsuaN: same idea as /dev/vcsaN for unicode (not yet implemented).
*
* 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/export.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/sched.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/signal.h>
#include <linux/slab.h>
#include <linux/notifier.h>
#include <linux/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)
/*
* Our minor space:
*
* 0 ... 63 glyph mode without attributes
* 64 ... 127 unicode mode without attributes
* 128 ... 191 glyph mode with attributes
* 192 ... 255 unused (reserved for unicode with attributes)
*
* This relies on MAX_NR_CONSOLES being <= 63, meaning 63 actual consoles
* with minors 0, 64, 128 and 192 being proxies for the foreground console.
*/
#if MAX_NR_CONSOLES > 63
#warning "/dev/vcs* devices may not accommodate more than 63 consoles"
#endif
#define console(inode) (iminor(inode) & 63)
#define use_unicode(inode) (iminor(inode) & 64)
#define use_attributes(inode) (iminor(inode) & 128)
struct vcs_poll_data {
struct notifier_block notifier;
unsigned int cons_num;
int event;
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;
int fa_band;
switch (code) {
case VT_UPDATE:
fa_band = POLL_PRI;
break;
case VT_DEALLOCATE:
fa_band = POLL_HUP;
break;
default:
return NOTIFY_DONE;
}
if (currcons == 0)
currcons = fg_console;
else
currcons--;
if (currcons != vc->vc_num)
return NOTIFY_DONE;
poll->event = code;
wake_up_interruptible(&poll->waitq);
kill_fasync(&poll->fasync, SIGIO, fa_band);
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, *kill = NULL;
if (poll)
return poll;
poll = kzalloc(sizeof(*poll), GFP_KERNEL);
if (!poll)
return NULL;
poll->cons_num = console(file_inode(file));
init_waitqueue_head(&poll->waitq);
poll->notifier.notifier_call = vcs_notifier;
/*
* In order not to lose any update event, we must pretend one might
* have occurred before we have a chance to register our notifier.
* This is also how user space has come to detect which kernels
* support POLLPRI on /dev/vcs* devices i.e. using poll() with
* POLLPRI and a zero timeout.
*/
poll->event = VT_UPDATE;
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 */
kill = poll;
poll = file->private_data;
}
spin_unlock(&file->f_lock);
if (kill)
vcs_poll_data_free(kill);
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 = console(inode);
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;
struct vc_data *vc;
WARN_CONSOLE_UNLOCKED();
vc = vcs_vc(inode, NULL);
if (!vc)
return -ENXIO;
size = vc->vc_rows * vc->vc_cols;
if (use_attributes(inode)) {
if (use_unicode(inode))
return -EOPNOTSUPP;
size = 2*size + HEADER_SIZE;
} else if (use_unicode(inode))
size *= 4;
return size;
}
static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
{
int size;
console_lock();
size = vcs_size(file_inode(file));
console_unlock();
if (size < 0)
return size;
return fixed_size_llseek(file, offset, orig, size);
}
static ssize_t
vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
struct inode *inode = file_inode(file);
struct vc_data *vc;
struct vcs_poll_data *poll;
long pos, read;
int attr, uni_mode, row, 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();
uni_mode = use_unicode(inode);
attr = use_attributes(inode);
ret = -ENXIO;
vc = vcs_vc(inode, &viewed);
if (!vc)
goto unlock_out;
ret = -EINVAL;
if (pos < 0)
goto unlock_out;
/* we enforce 32-bit alignment for pos and count in unicode mode */
if (uni_mode && (pos | count) & 3)
goto unlock_out;
poll = file->private_data;
if (count && poll)
poll->event = 0;
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 (uni_mode) {
unsigned int nr;
ret = vc_uniscr_check(vc);
if (ret)
break;
p /= 4;
row = p / vc->vc_cols;
col = p % maxcol;
nr = maxcol - col;
do {
if (nr > this_round/4)
nr = this_round/4;
vc_uniscr_copy_line(vc, con_buf0, viewed,
row, col, nr);
con_buf0 += nr * 4;
this_round -= nr * 4;
row++;
col = 0;
nr = maxcol;
} while (this_round);
} else 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;
/* clamp header values if they don't fit */
con_buf0[0] = min(vc->vc_rows, 0xFFu);
con_buf0[1] = min(vc->vc_cols, 0xFFu);
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_inode(file);
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;
if (use_unicode(inode))
return -EOPNOTSUPP;
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 = use_attributes(inode);
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 __poll_t
vcs_poll(struct file *file, poll_table *wait)
{
struct vcs_poll_data *poll = vcs_poll_data_get(file);
__poll_t ret = DEFAULT_POLLMASK|EPOLLERR;
if (poll) {
poll_wait(file, &poll->waitq, wait);
switch (poll->event) {
case VT_UPDATE:
ret = DEFAULT_POLLMASK|EPOLLPRI;
break;
case VT_DEALLOCATE:
ret = DEFAULT_POLLMASK|EPOLLHUP|EPOLLERR;
break;
case 0:
ret = DEFAULT_POLLMASK;
break;
}
}
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 = console(inode);
bool attr = use_attributes(inode);
bool uni_mode = use_unicode(inode);
int ret = 0;
/* we currently don't support attributes in unicode mode */
if (attr && uni_mode)
return -EOPNOTSUPP;
console_lock();
if(currcons && !vc_cons_allocated(currcons-1))
ret = -ENXIO;
console_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 + 65), NULL,
"vcsu%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 + 65));
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, 64), NULL, "vcsu");
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;
}
