bionic (4) snp.4freebsd.gz

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.