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CNMAGIC(9) Kernel Developer's Manual CNMAGIC(9)

cn_init_magic, cn_trap, cn_isconsole, cn_check_magic, cn_destroy_magic, cn_set_magic, cn_get_magic — console magic key sequence management

#include <sys/systm.h>

void
cn_init_magic(cnm_state_t *cnms);

void
cn_trap();

int
cn_isconsole(dev_t dev);

void
cn_check_magic(dev_t dev, int k, cnm_state_t *cnms);

void
cn_destroy_magic(cnm_state_t *cnms);

int
cn_set_magic(char *magic);

int
cn_get_magic(char *magic, int len);

The NetBSD console magic key sequence management framework is designed to provide flexible methods to set, change, and detect magic key sequences on console devices and break into the debugger or ROM monitor with a minimum of interrupt latency.

Drivers that generate console input should make use of these routines. A different cnm_state_t should be used for each separate input stream. Multiple devices that share the same input stream, such as USB keyboards, can share the same cnm_state_t. Once a cnm_state_t is allocated, it should be initialized with () so it can be used by (). If a driver thinks it might be the console input device it can set the magic sequence with cn_set_magic() to any arbitrary string. Whenever the driver receives input, it should call cn_check_magic() to process the data and determine whether the magic sequence has been hit.

The magic key sequence can be accessed through the hw.cnmagic sysctl variable. This is the raw data and may be keycodes rather than processed characters, depending on the console device.

The following functions describe the console magic interface.

(cnm)
Initialize the console magic state pointed to by cnm to a usable state.
()
Trap into the kernel debugger or ROM monitor. By default this routine is defined to be () but can be overridden in MI header files.
(dev)
Determine whether a given dev is the system console. This macro tests to see if dev is the same as cn_tab->cn_dev but can be overridden in MI header files.
cn_check_magic(dev, k, cnms)
All input should be passed through cn_check_magic() so the state machine remains in a consistent state. cn_check_magic() calls cn_isconsole() with dev to determine if this is the console. If that returns true then it runs the input value k through the state machine. If the state machine completes a match of the current console magic sequence cn_trap() is called. Some input may need to be translated to state machine values such as the serial line BREAK sequence.
(cnms)
This should be called once what cnms points to is no longer needed.
cn_set_magic(magic)
cn_set_magic() encodes a nul terminated arbitrary string into values that can be used by the state machine and installs it as the global magic sequence. The escape sequence is character value 0x27 and can be used to encode special values:

0x27
The literal value 0x27.
0x01
Serial BREAK sequence.
0x02
character.

Returns 0 on success or a non-zero error value.

(magic, len)
Extract the current magic sequence from the state machine and return up to len bytes of it in the buffer pointed to by magic. It uses the same encoding accepted by (). Returns 0 on success or a non-zero error value.

ddb(4), sysctl(8), cons(9)

The NetBSD console magic key sequence management framework first appeared in NetBSD 1.6.

The NetBSD console magic key sequence management framework was designed and implemented by Eduardo Horvath ⟨eeh@NetBSD.org⟩.

July 7, 2019 NetBSD-9.2