devctl(4)

NAME

devctl - device event reporting and device control interface

DESCRIPTION

The devctl device is used to report device events from the

kernel.
Future versions will allow for some device control as well.

IMPLEMENTATION NOTES

This design allows only one reader for /dev/devctl. This is

not desirable in the long run, but will get a lot of hair out of this

implementation. Maybe we should make this device a clonable device.

Also note: we specifically do not attach a device to the

device_t tree to
avoid potential chicken and egg problems. One could argue

that all of
this belongs to the root node. One could also further argue

that the
sysctl(3) interface that we have now might more properly be

an ioctl(2)
interface.

SIGIO support is included in the driver. However, the au

thor is not sure
that the SIGIO support is done correctly. It was copied

from a driver
that had SIGIO support that likely has not been tested since

FreeBSD 3.4
or FreeBSD 2.2.8!

The read channel for this device is used to report changes

to userland in
realtime. We return one record at a time. If you try to

read this
device a character at a time, you will loose the rest of the

data. Listening programs are expected to cope.

The sysctl and boot parameter hw.bus.devctl_disable is used

to disable
devctl when no devd(8) is running.

PROTOCOL

The devctl device uses an ASCII protocol. The driver re

turns one record
at a time to its readers. Each record is terminated with a

newline. The
first character of the record is the event type.

Type Description
! A notify event, such as a link state change.
+ Device node in tree attached.
- Device node in tree detached.
? Unknown device detected.

Message Formats

Except for the first character in the record, attach and de

tach messages
have the same format.

Tdev at parent on location

Part Description
T + or dev The device name that was attached/detached.
parent The device name of the parent bus that attached

the device.
location Bus specific location information.

The nomatch messages can be used to load devices driver. If

you load a
device driver, then one of two things can happen. If the

device driver
attaches to something, you will get a device attached mes

sage. If it
does not, then nothing will happen.

The attach and detach messages arrive after the event. This

means one
cannot use the attach message to load an alternate driver.

The attach
message driver has already claimed this device. One cannot

use the
detach messages to flush data to the device. The device is

already gone.

SEE ALSO

devd(8)

BSD January 23, 2006

BSD