kbdfs – keyboard and console filesystem

aux/kbdfs [ –Dd ] [ –s srv ] [ –m mntpnt ] [ filename ]
mount –b /srv/cons /dev


Started on boot(8), kbdfs translates raw keyboard scancodes from /dev/scancode (see kbd(3)) and its kbin and kbdin file and optionally reads console input from consfile to provide initial keyboard and console input.

It serves a one–level directory containing the files cons, consctl, kbd, kbdin, kbin and kbmap.

The –D flag enables a debug trace of 9p messages and –d prevents kbdfs from making its memory private.

The –s option causes kbdfs to post its channel on /srv/srv. On system startup, boot(8) sets this to cons. With the –m option, kbdfs mounts itself on mntpnt (see bind(2)), otherwise on /dev (the default).


Reading the cons file returns characters typed on the console. Normally, characters are buffered to enable erase and kill processing. A control–U, ^U, typed at the keyboard erases the current input line (removes all characters from the buffer of characters not yet read via cons), and a backspace erases the previous non–kill, non–erase character from the input buffer. The combination control–W, ^W, deletes the input last word. Killing and erasing only delete characters back to, but not including, the last newline. Characters typed at the keyboard actually produce 16–bit runes (see utf(6)), but the runes are translated into the variable–length UTF encoding (see utf(6)) before putting them into the buffer. A read(2) of a length greater than zero causes the process to wait until a newline or a ^D ends the buffer, and then returns as much of the buffer as the argument to read allows, but only up to one complete line. A terminating ^D is not put into the buffer. If part of the line remains, the next read will return bytes from that remainder and not part of any new line that has been typed since.

If the string rawon has been written to the consctl file and the file is still open, cons is in raw mode: characters are not echoed as they are typed, backspace, ^U, ^W and ^D are not treated specially, and characters are available to read as soon as they are typed. Ordinary mode is reentered when rawoff is written to consctl or this file is closed.

A write (see read(2)) to cons causes the characters to be printed on the console screen.

When a filename is passed to kbdfs(8) as its last argument, it reads and processes the characters from that file and forwards them to the cons file with the same text processing applied as on keyboard input. This is used on serial consoles.

A read on the kbd file returns the character k, K or c followed by a null terminated, variable–length, UTF encoded string. The k message is send when a key is pressed down and K when a key is released. The following string contains all the keycodes of the keys that are currently pressed down in unshifted form. This includes all keys that have a keyboard mapping and modifier keys. The string following the c message contains the single character that would have been returned on the cons file instead. The c message will be resent at the keyboard repeat rate. A single read(2) can return multiple concatenated messages at once (delimited by the null byte) or block when there are no messages queued. Opening the kbd file disables input processing on the cons file until it is closed again.

K, k and c messages can be written to kbdin and will forwarded to the reader of cons or kbd. Writing a r or R message followed by a UTF encoded rune will simulate the press or release of that particular rune.

Raw scancodes can be written to the kbin file for external keyboard input (used for USB keyboards).

Keyboard map
Scancodes are mapped to Unicode characters with a number of translation tables. These tables can be accessed with the kbmap file.

Reads return the current contents of the map. Each entry is one line containing three 11 character numeric fields, each followed by a space: a table number, an index into the table (scan code), and the decimal value of the corresponding Unicode character (0 if none). The table numbers are platform dependent; they typically distinguish between unshifted and shifted keys. The scan code values are hardware dependent and can vary from keyboard to keyboard.

Writes to the file change the map. Lines written to the file must contain three space–separated fields, representing the table number, scan code index, and Unicode character. Values are taken to be decimal unless they start with 0x (hexadecimal) or 0 (octal). The Unicode character can also be represented as 'x where x gives the UTF–8 representation of the character (see utf(6)), or as ^X to represent a control character.

cons(3), keyboard(6), utf(6), kbd(3)



Kbdfs first appeared in 9front (May, 2011).