devctl(4) [debian man page]

DEVCTL(4)						   BSD Kernel Interfaces Manual 						 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 implemen-
     tation.  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 author 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 lose 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 returns 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 detach 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 message.  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
								 February 11, 2003							       BSD

Check Out this Related Man Page

SNP(4)                                                     BSD Kernel Interfaces Manual                                                     SNP(4)

NAME

     snp -- tty snoop interface

SYNOPSIS

     #include <sys/snoop.h>

     int
     ioctl(fd, SNPSTTY, &dev);

     int
     ioctl(fd, SNPGTTY, &dev);

     int
     ioctl(fd, FIONREAD, &result);

DESCRIPTION

     /dev/snp is a snoop device which allows users to attach to any tty and watch activities on it.  The kernel must be compiled with device snp,
     or the snp module must be loaded, for these devices to be available.

     To associate a given snp device with a tty to be observed, open the snp device and a tty device, and then issue the SNPSTTY ioctl on snp
     device.  The argument passed to the ioctl(2) is the address of a variable of type int, holding the file descriptor of a tty device.  To
     detach the snp device from a tty use a pointer to a value of -1.

     The SNPGTTY ioctl returns information about the current tty attached to the open snp device.

     The FIONREAD ioctl returns a positive value equal to the number of characters in a read buffer.  Special values defined are:

     SNP_OFLOW     device overflow occurred, device detached.

     SNP_TTYCLOSE  tty not attached.

     SNP_DETACH    snp device has been detached by user or tty device has been closed and detached.

SEE ALSO

     pty(4), sio(4), kldload(8), watch(8)

HISTORY

     The snp device first appeared in FreeBSD 2.1.  In FreeBSD 8.0 the snp driver was rewritten to work with the replaced TTY subsystem.

AUTHORS

     The author of the current implementation is Ed Schouten <ed@FreeBSD.org>.  Previous versions of snp were based on code written by
     Ugen J.S. Antsilevich <ugen@NetVision.net.il>.

BUGS

     This version of snp does not return proper error codes when calling FIONREAD.  It also does not allow SNPSTTY to detach itself from the TTY.

BSD                                                              November 5, 2008                                                              BSD

Linux and UNIX Man Pages

devctl(4) [debian man page]

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