Inner-workings of Keyboard Event Handling under Linux -

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when press keyboard's key on gtk application under linux, happens exactly? how key received (from device), interpreted, passed program, , handled?

it's rather complex process...

  1. the keyboard has 2d matrix of key connections , own microprocessor or gate array containing microprocessor. scanning matrix find out if keys pressed. (to save pins, keys not individually tested.) keyboard micro speaks protocol keyboard controller in cpu , transmits message indicating keypress.
  2. the keyboard controller notes code , interrupts cpu.
  3. the keyboard driver receives interrupt, reads keycode out of controller register, , places keycode in buffer links interrupt side of kernel per-process threads. marks thread waiting keyboard input "runnable"
  4. this thread wakes up. turns out, x server. x server reads keycode kernel.
  5. the server will check see window has keyboard focus. window connected 1 of various clients.
  6. the server sends event client displayed specific window. (note server, every textbox , such "window", not entire applications.)
  7. the event loop in client waiting next server event message. connection via tcp or local unix feature. uses read(2) or socket op next event message.
  8. the low-level xlib routine passes keypress higher level widgets, getting gtk function of kind.
  9. the gtk api element hands character program.

i glossed on language mappings, console multiplexing, , few other things...

update: so, /dev/input/* , in fact of /dev/* things things called block or character special files. important thing have no stored data in filesystem, major , minor device number serve driver in kernel in table. it's simple. if ls -l /dev/input see major , minor device number instead of file size. major number identifies device driver , minor number sort of instance-number passed (within kernel) parameter driver.


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