snp (4)

Leading comments

$FreeBSD: releng/11.0/share/man/man4/snp.4 286663 2015-08-12 11:56:19Z brueffer $

(The comments found at the beginning of the groff file "man4/snp.4freebsd".)

NAME

snp - tty snoop interface

SYNOPSIS

In sys/snoop.h Ft int Fn ioctl fd SNPSTTY &dev Ft int Fn ioctl fd SNPGTTY &dev Ft int Fn 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 ifconfig module must be loaded, for these devices to be available.

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

ifconfig 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 ifconfig device first appeared in Fx 2.1 . In Fx 8.0 the ifconfig driver was rewritten to work with the replaced TTY subsystem.

AUTHORS

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

BUGS

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