SchOS/kernel/dev/input.c

// Raw input event devices -- /dev/input/event0 and /dev/input/event1.
//
// Everything that produces input feeds this: the PS/2 keyboard and mouse, and
// the USB HID driver. The console keeps its own path and is unaffected; these
// nodes are a *second* consumer of the same interrupts, so a program can read
// keys while the shell still gets characters.
//
// Two devices rather than one because they are two devices. A compositor
// grabs the pointer and leaves the keyboard alone, or the other way round, and
// merging them into a single stream makes that impossible to express.

#include "types.h"
#include "defs.h"
#include "param.h"
#include "mmu.h"
#include "proc.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "fs.h"
#include "file.h"
#include "input.h"
#include "errno.h"

#define NEVENT 256              // per device; ~10 seconds of frantic typing

struct input_dev {
  struct spinlock lock;
  struct input_event ev[NEVENT];
  uint r, w;                    // free-running; the difference is the count

  // Exclusive grab (EVIOCGRAB). While set, keys still arrive here but stop
  // being handed to the console's line discipline.
  //
  // Without this a full-screen program does not really own the keyboard: it
  // reads /dev/input/event0 *and* the shell behind it reads the same keystrokes
  // off the tty. The observed failure was a full-screen program quietly typing
  // its entire session into the shell underneath, so the first Enter after
  // exiting ran whatever had accumulated. The grab is also exactly what a
  // compositor needs, which is why it lives here rather than in any one client.
  int grabbed;

  // How many descriptors are open on this device.
  //
  // Events are only queued while this is non-zero, and the backlog is dropped
  // on the first open. Both halves matter: without them the ring is a log of
  // every key pressed since boot, and the next program to open the device is
  // handed the lot as though the user had just typed it.
  int opens;
};

static struct input_dev idev[NINPUTDEV];
static int input_up;

extern uint ticks;

void
inputinit(void)
{
  int i;

  for(i = 0; i < NINPUTDEV; i++)
    initlock(&idev[i].lock, "input");

  // Producers run from interrupt handlers and can fire before this point in
  // boot. Until the locks exist, an event has nowhere safe to go.
  __sync_synchronize();
  input_up = 1;
}

// Append one event. Called from interrupt context, so it never sleeps and
// never blocks on a full ring.
void
input_report(int dev, int type, int code, int value)
{
  struct input_dev *d;
  struct input_event *e;

  if(!input_up || dev < 0 || dev >= NINPUTDEV)
    return;
  d = &idev[dev];

  // Nobody is listening, so there is nowhere for this to go. Linux does the
  // same: an evdev device with no clients does not accumulate.
  if(d->opens == 0)
    return;

  acquire(&d->lock);

  // A full ring drops the *oldest* event, not the newest. Dropping the newest
  // is the obvious choice and it is wrong: the event most likely to be lost is
  // then a key release, and a lost release leaves the key held down forever
  // as far as every reader is concerned. Losing the oldest costs history, not
  // state.
  if(d->w - d->r >= NEVENT)
    d->r++;

  e = &d->ev[d->w % NEVENT];
  e->time.tv_sec  = ticks / 100;
  e->time.tv_usec = (ticks % 100) * 10000;
  e->type  = (uint16)type;
  e->code  = (uint16)code;
  e->value = (int32)value;
  d->w++;

  release(&d->lock);
}

// End a report. A reader that acts on each event as it arrives will see a
// diagonal mouse move as two separate moves; the SYN is how it knows the two
// axes belong to the same physical motion.
void
input_sync(int dev)
{
  if(!input_up || dev < 0 || dev >= NINPUTDEV)
    return;
  input_report(dev, EV_SYN, SYN_REPORT, 0);
  wakeup(&idev[dev]);
}

int
input_ready(int dev)
{
  int n;

  if(!input_up || dev < 0 || dev >= NINPUTDEV)
    return 0;
  acquire(&idev[dev].lock);
  n = idev[dev].w != idev[dev].r;
  release(&idev[dev].lock);
  return n;
}

// A descriptor has been opened on this device.
//
// The backlog is discarded, which is the whole point. Events queued before a
// program opened the device were meant for whoever had it *then* -- almost
// always the shell, which already consumed them as a command line. Replaying
// them into the new owner means a program is handed the keystrokes that
// launched it, as input, the instant it starts. That was a real crash and not a
// cosmetic one: the replayed characters were interpreted as commands, and one of
// them asked for a mode the program had not initialised yet.
//
// Linux gets this for free by giving every open its own client queue. One
// shared ring plus "start from now" is the same answer for a single reader,
// which is the case that exists.
void
inputopen(struct inode *ip)
{
  int dev = ip->minor;

  if(dev < 0 || dev >= NINPUTDEV)
    return;
  acquire(&idev[dev].lock);
  idev[dev].opens++;
  idev[dev].r = idev[dev].w;          // start from now, not from boot
  release(&idev[dev].lock);
}

// The devsw ready hook: would a read block?
int
inputready(struct inode *ip)
{
  return input_ready(ip->minor);
}

// Is this device grabbed? Asked by the keyboard drivers before they hand a
// character to the console.
int
input_is_grabbed(int dev)
{
  if(!input_up || dev < 0 || dev >= NINPUTDEV)
    return 0;
  return idev[dev].grabbed;
}

// EVIOCGRAB. Linux's semantics: one holder at a time, and it is not an error
// to grab what you already hold.
int
input_grab(int dev, int on)
{
  if(!input_up || dev < 0 || dev >= NINPUTDEV)
    return -ENODEV;
  on = on ? 1 : 0;
  if(idev[dev].grabbed != on){
    idev[dev].grabbed = on;
    // Said out loud. A grabbed keyboard is a console that has gone deaf on
    // purpose, and that is indistinguishable from one that has gone deaf by
    // accident unless the kernel says which it was.
    cprintf("input: event%d %s by pid %d\n", dev,
            on ? "grabbed" : "released", myproc() ? myproc()->pid : -1);
  }
  return 0;
}

// The last descriptor on this device is going away.
//
// Releasing the grab here is not tidiness, it is the difference between a
// crashed game and a machine you have to reboot: a program that grabs the
// keyboard and dies without ungrabbing would leave the console permanently
// deaf. The close hook makes the release unconditional.
void
inputclose(struct inode *ip)
{
  int dev = ip->minor;

  if(dev < 0 || dev >= NINPUTDEV)
    return;
  if(idev[dev].opens > 0)
    idev[dev].opens--;
  if(idev[dev].grabbed){
    idev[dev].grabbed = 0;
    cprintf("input: event%d grab released\n", dev);
  }
}

// ioctl on /dev/input/eventN. Only EVIOCGRAB so far; the EVIOCG* query
// requests (name, id, capability bitmaps) can arrive when something needs
// them.
int
input_ioctl(struct inode *ip, int request, addr_t arg)
{
  int on;

  if(request == EVIOCGRAB){
    // Linux passes the flag *by value* in the argument, not by pointer.
    on = (int)arg;
    return input_grab(ip->minor, on);
  }
  return -ENOTTY;
}

// A read returns whole events only. Handing back a partial struct would
// desynchronise the reader permanently -- every later event would be split
// across two reads and reassembled wrong.
int
inputread(struct inode *ip, uint off, char *dst, int n)
{
  struct input_dev *d;
  int got = 0;
  int dev = ip->minor;

  if(dev < 0 || dev >= NINPUTDEV)
    return -ENODEV;
  if(n < (int)sizeof(struct input_event))
    return -EINVAL;
  d = &idev[dev];

  acquire(&d->lock);
  while(d->r == d->w){
    if(myproc()->killed){
      release(&d->lock);
      return -EINTR;
    }
    sleep(d, &d->lock);
  }

  while(d->r != d->w && got + (int)sizeof(struct input_event) <= n){
    memmove(dst + got, &d->ev[d->r % NEVENT], sizeof(struct input_event));
    d->r++;
    got += sizeof(struct input_event);
  }
  release(&d->lock);
  return got;
}

// evdev accepts writes to set keyboard LEDs. There are no LEDs to set here,
// and a program that writes one should not see an error for it.
int
inputwrite(struct inode *ip, uint off, char *src, int n)
{
  return n;
}

// ---------------------------------------------------------------------------
// Producers
// ---------------------------------------------------------------------------

// AT scancode set 1, E0-prefixed. The unprefixed bytes need no table at all:
// Linux's keycodes were numbered from this set and still match it below 0x54.
// These are the ones that do not.
static const struct { uint8 sc; uint8 key; } e0map[] = {
  {0x1C, 96},                   // KP_ENTER
  {0x1D, KEY_RIGHTCTRL},
  {0x35, 98},                   // KP_SLASH
  {0x38, KEY_RIGHTALT},
  {0x47, KEY_HOME},
  {0x48, KEY_UP},
  {0x49, KEY_PAGEUP},
  {0x4B, KEY_LEFT},
  {0x4D, KEY_RIGHT},
  {0x4F, KEY_END},
  {0x50, KEY_DOWN},
  {0x51, KEY_PAGEDOWN},
  {0x52, KEY_INSERT},
  {0x53, KEY_DELETE},
  {0x5B, KEY_LEFTMETA},
  {0x5C, KEY_RIGHTMETA},
};

// One byte from the PS/2 port, before it has been turned into a character.
void
input_ps2_scancode(int raw, int e0)
{
  int code = raw & 0x7F;
  int down = (raw & 0x80) ? 0 : 1;
  int key = 0;
  unsigned i;

  if(e0){
    for(i = 0; i < sizeof(e0map)/sizeof(e0map[0]); i++)
      if(e0map[i].sc == code){
        key = e0map[i].key;
        break;
      }
    if(key == 0)
      return;                   // an E0 key nothing has a name for
  } else {
    if(code == 0 || code > 0x58)
      return;
    key = code;
  }

  input_report(INPUT_KBD, EV_KEY, key, down);
  input_sync(INPUT_KBD);
}

// USB HID usage -> Linux keycode. The mapping is not derivable: HID numbers
// keys by position on a US layout starting at 'a', and the AT set numbers them
// by the order IBM wired the matrix. The table is the same one Linux carries
// for the same reason.
static const uint8 hid_keycode[] = {
    0,  0,  0,  0, 30, 48, 46, 32, 18, 33, 34, 35, 23, 36, 37, 38,
   50, 49, 24, 25, 16, 19, 31, 20, 22, 47, 17, 45, 21, 44,  2,  3,
    4,  5,  6,  7,  8,  9, 10, 11, 28,  1, 14, 15, 57, 12, 13, 26,
   27, 43, 43, 39, 40, 41, 51, 52, 53, 58, 59, 60, 61, 62, 63, 64,
   65, 66, 67, 68, 87, 88, 99, 70,119,110,102,104,111,107,109,106,
  105,108,103, 69, 98, 55, 74, 78, 96, 79, 80, 81, 75, 76, 77, 71,
   72, 73, 82, 83, 86,127,116,117,
};

// The eight modifier bits in a boot report, in bit order.
static const uint8 hid_modkey[8] = {
  KEY_LEFTCTRL, KEY_LEFTSHIFT, KEY_LEFTALT, KEY_LEFTMETA,
  KEY_RIGHTCTRL, KEY_RIGHTSHIFT, KEY_RIGHTALT, KEY_RIGHTMETA,
};

int
input_hid_keycode(int usage)
{
  if(usage >= 0xE0 && usage <= 0xE7)
    return hid_modkey[usage - 0xE0];
  if(usage < 0 || usage >= (int)sizeof(hid_keycode))
    return 0;
  return hid_keycode[usage];
}

void
input_key(int usage, int down)
{
  int key = input_hid_keycode(usage);

  if(key == 0)
    return;
  input_report(INPUT_KBD, EV_KEY, key, down);
  input_sync(INPUT_KBD);
}

// One mouse report: relative motion plus the current button state. `buttons`
// is a bitmask in the order both PS/2 and HID boot protocol use -- left,
// right, middle -- which is why neither caller has to reorder it.
// An absolute pointer: where it is, not how far it moved.
//
// A relative device can never agree with the host's cursor inside a VM -- the
// two accumulate independently and drift apart, which is exactly the symptom
// usb-tablet exists to remove. Reported as EV_ABS so a reader can tell the
// difference and treat the value as authoritative rather than as a delta.
void
input_mouse_abs(int x, int y, int buttons)
{
  static int last;
  static int lastx = -1, lasty = -1;
  static const int btncode[3] = { BTN_LEFT, BTN_RIGHT, BTN_MIDDLE };
  int i;

  if(x != lastx){ input_report(INPUT_MOUSE, EV_ABS, ABS_X, x); lastx = x; }
  if(y != lasty){ input_report(INPUT_MOUSE, EV_ABS, ABS_Y, y); lasty = y; }

  for(i = 0; i < 3; i++){
    int now = (buttons >> i) & 1, was = (last >> i) & 1;
    if(now != was)
      input_report(INPUT_MOUSE, EV_KEY, btncode[i], now);
  }
  last = buttons;

  input_report(INPUT_MOUSE, EV_SYN, SYN_REPORT, 0);
}

void
input_mouse(int dx, int dy, int buttons)
{
  static int last;
  static const int btncode[3] = { BTN_LEFT, BTN_RIGHT, BTN_MIDDLE };
  int i;

  if(dx)
    input_report(INPUT_MOUSE, EV_REL, REL_X, dx);
  if(dy)
    input_report(INPUT_MOUSE, EV_REL, REL_Y, dy);

  // Only transitions. A button held down for a second is one press event, not
  // a hundred -- a reader that has to filter repeats itself cannot tell a held
  // button from a very fast double-click.
  for(i = 0; i < 3; i++){
    int now = (buttons >> i) & 1;
    if(now != ((last >> i) & 1))
      input_report(INPUT_MOUSE, EV_KEY, btncode[i], now);
  }
  last = buttons;

  input_sync(INPUT_MOUSE);
}