vc_screen.c

Go to the documentation of this file.

/*
 * 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.
 *
 * [email protected] - efter Friedas begravelse - 950211
 *
 * [email protected] - 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 <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;
    
    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 + 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;
}