/dev/snp? are snoop devices which allow users to attach to any tty and watch activities on it. The kernel must be compiled with
.Cd "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
.Vt 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: