CONS(3) CONS(3)
NAME
cons - console device
SYNOPSIS
bind #c /dev
/dev/cons
/dev/consctl
/dev/drivers
/dev/jit
/dev/keyboard
/dev/klog
/dev/kprint
/dev/memory
/dev/msec
/dev/null
/dev/notquiterandom
/dev/pointer
/dev/random
/dev/scancode
/dev/sysctl
/dev/sysname
/dev/time
/dev/user
DESCRIPTION
The console device serves a one-level directory giving
access to the console and miscellaneous information.
Reading the cons file returns characters typed on the key-
board. Normally, characters are buffered to enable erase
and kill processing. A control-U, `^U', typed at the key-
board kills 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. Killing and erasing only delete
characters back to, but not including, the last newline.
Typed keystrokes produce 21-bit runes that are translated
into the variable-length UTF encoding (see utf(6)) before
putting them into the buffer. A read of 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. A single line containing a `^D' can be
used as an end of file indication to programs that take
interactive input.
Page 1 Plan 9 (printed 12/23/24)
CONS(3) CONS(3)
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' 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 to cons causes the characters to be printed on the
console screen.
The keyboard file returns the underlying tokens produced by
the keyboard hardware as they are produced; in the emulation
environment, it is like an always-raw cons file.
The null file throws away anything written to it and always
returns zero bytes when read.
The klog file returns the tail of messages written by the
native kernel debugging function kprint (mainly used when
debugging interrupt handlers in device drivers). It is
available only in native kernel implementations.
The kprint file returns console output: messages written by
kernel print statements and messages written by processes to
this driver's cons file. Until kprint is opened, system
console output is handled normally. Once kprint has been
opened, if the machine's console is a serial line, the data
is sent both to the serial console and to kprint; if the
console is a graphics screen, the data is sent only to
kprint.
A read of the pointer file returns the status of the mouse
or other pointing device: its position and button state.
The read blocks until the state has changed since the last
read. The read returns 49 bytes: the letter m followed by
four fields containing decimal integers, each 11 characters
wide followed by a blank. The integers are: x and y, coor-
dinates of the pointer on the screen; a bit mask with the 1,
2, and 4 bits when the pointer's left, middle, and right
buttons, respectively, are down; and a time stamp in units
of milliseconds.
Writing to the pointer file, using the same format, causes
the pointer to move to the specified x, y position (the but-
ton and millisecond fields are ignored, and optional). If
there is a visible image representing the pointer's posi-
tion, that will move too.
The random device returns as many bytes of random data as
are requested in the read.
The notquiterandom device returns as many bytes of pseudo-
Page 2 Plan 9 (printed 12/23/24)
CONS(3) CONS(3)
random data as are requested in the read; this is typically
faster than random but the results are more predictable.
The scancode device provides access to the raw scan codes of
the primary keyboard . While it is open, key strokes are
diverted from cons and keyboard . The first read(2) after
opening returns an identifier string which defines the for-
mat of data delivered by subsequent reads. Known ones are
defined in scancode(6). The most common format is a single
byte per scan code, where the top bit is 1 for up and 0 for
down, and the bottom 7 bits are the scan code. Some input
devices have a larger scan code space; in this case scan
codes are often delivered as two byte little endian quanti-
ties, where the top bit is the up/down signifier, and the
bottom 15 bits are the scan code. In all cases the meaning
of the individual scan codes is device specific.
The rest of the files contain (mostly) read-only strings.
Each string has a fixed length: a read (see sys-read(2)) of
more than that gives a result of that fixed length (the
result does not include a terminating zero byte); a read of
less than that length leaves the file offset so the rest of
the string (but no more) will be read the next time. To
reread the file without closing it, seek must be used to
reset the offset. When the file contains numeric data, each
number is formatted in decimal as an 11-digit number with
leading blanks and one trailing blank: twelve bytes total.
The sysctl file can be read to return the current Inferno
version. Writing the string reboot to it attempts to reboot
the system, writing halt attempts to halt the system. Writ-
ing nobroken ensures that broken processes have all associ-
ated memory freed before being destroyed, writing broken
ensures that they are left in this state to allow debugging
(the default). Only the privileged user is allowed to write
to this file.
The sysname file holds the textual name of the machine. It
can only be written by the privileged user.
The user file contains the name of the user associated with
the current process. It can only be written by the privi-
leged user. In the emulation environment, writing to this
file also attempts to set the user id in the host operating
system to the specified value.
The memory file returns a formatted presentation of the
state of the memory allocation pools in the system. Each
line of output returned reports, for a single pool, the
amount of memory in use, the upper size limit, the high
water mark, the number of allocations done, the number of
frees done, the number of extensions done, the largest chunk
Page 3 Plan 9 (printed 12/23/24)
CONS(3) CONS(3)
available and the name of the pool.
The drivers file returns a list of the device drivers loaded
in the system. Each line gives the name of the device for
bind(1), such as #c, followed by the name of the driver as
used in the system configuration file.
The other files served by the cons device are all single
numbers:
jit non-zero if `just in time' compilation is configured
(can be written to change the state). Writing 0 turns
off JIT compilation, 1 turns it on and larger values
give increasingly detailed traces of the compilation
for debugging purposes.
msec the value of a millisecond counter
time number of microseconds since the epoch 00:00:00 GMT,
Jan. 1, 1970. (Can be written once by the privileged
user, to set at boot time.)
SOURCE
/emu/port/devcons.c
/os/port/devcons.c
SEE ALSO
draw(3), keyboard(6), utf(6), eve(10.2)
BUGS
For debugging, on native systems only, two control-T's fol-
lowed by a letter generate console output: `^T^Tp' prints
data about kernel processes, `^T^Ts' prints the kernel
stack, `^T^Tx' prints data about memory allocation.
The system can be rebooted by typing `^T^Tr'.
Page 4 Plan 9 (printed 12/23/24)