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vc_screen.c

/*
 * 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/mutex.h>
#include <linux/vt_kern.h>
#include <linux/selection.h>
#include <linux/kbd_kern.h>
#include <linux/console.h>
#include <linux/device.h>

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

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

static int
vcs_size(struct inode *inode)
{
      int size;
      int minor = iminor(inode);
      int currcons = minor & 127;
      struct vc_data *vc;

      if (currcons == 0)
            currcons = fg_console;
      else
            currcons--;
      if (!vc_cons_allocated(currcons))
            return -ENXIO;
      vc = vc_cons[currcons].d;

      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;

      mutex_lock(&con_buf_mtx);
      size = vcs_size(file->f_path.dentry->d_inode);
      switch (orig) {
            default:
                  mutex_unlock(&con_buf_mtx);
                  return -EINVAL;
            case 2:
                  offset += size;
                  break;
            case 1:
                  offset += file->f_pos;
            case 0:
                  break;
      }
      if (offset < 0 || offset > size) {
            mutex_unlock(&con_buf_mtx);
            return -EINVAL;
      }
      file->f_pos = offset;
      mutex_unlock(&con_buf_mtx);
      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;
      long pos;
      long viewed, attr, read;
      int col, maxcol;
      unsigned short *org = NULL;
      ssize_t ret;

      mutex_lock(&con_buf_mtx);

      pos = *ppos;

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

      attr = (currcons & 128);
      currcons = (currcons & 127);
      if (currcons == 0) {
            currcons = fg_console;
            viewed = 1;
      } else {
            currcons--;
            viewed = 0;
      }
      ret = -ENXIO;
      if (!vc_cons_allocated(currcons))
            goto unlock_out;
      vc = vc_cons[currcons].d;

      ret = -EINVAL;
      if (pos < 0)
            goto unlock_out;
      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 (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().
             */

            release_console_sem();
            ret = copy_to_user(buf, con_buf_start, orig_count);
            acquire_console_sem();

            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:
      release_console_sem();
      mutex_unlock(&con_buf_mtx);
      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 viewed, attr, size, written;
      char *con_buf0;
      int col, maxcol;
      u16 *org0 = NULL, *org = NULL;
      size_t ret;

      mutex_lock(&con_buf_mtx);

      pos = *ppos;

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

      attr = (currcons & 128);
      currcons = (currcons & 127);

      if (currcons == 0) {
            currcons = fg_console;
            viewed = 1;
      } else {
            currcons--;
            viewed = 0;
      }
      ret = -ENXIO;
      if (!vc_cons_allocated(currcons))
            goto unlock_out;
      vc = vc_cons[currcons].d;

      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.
             */
            release_console_sem();
            ret = copy_from_user(con_buf, buf, this_round);
            acquire_console_sem();

            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 (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;

unlock_out:
      release_console_sem();

      mutex_unlock(&con_buf_mtx);

      return ret;
}

static int
vcs_open(struct inode *inode, struct file *filp)
{
      unsigned int currcons = iminor(inode) & 127;
      if(currcons && !vc_cons_allocated(currcons-1))
            return -ENXIO;
      return 0;
}

static const struct file_operations vcs_fops = {
      .llseek           = vcs_lseek,
      .read       = vcs_read,
      .write            = vcs_write,
      .open       = vcs_open,
};

static struct class *vc_class;

void vcs_make_sysfs(struct tty_struct *tty)
{
      device_create(vc_class, NULL, MKDEV(VCS_MAJOR, tty->index + 1),
                  "vcs%u", tty->index + 1);
      device_create(vc_class, NULL, MKDEV(VCS_MAJOR, tty->index + 129),
                  "vcsa%u", tty->index + 1);
}

void vcs_remove_sysfs(struct tty_struct *tty)
{
      device_destroy(vc_class, MKDEV(VCS_MAJOR, tty->index + 1));
      device_destroy(vc_class, MKDEV(VCS_MAJOR, tty->index + 129));
}

int __init vcs_init(void)
{
      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), "vcs");
      device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 128), "vcsa");
      return 0;
}

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