SNP(4) | Device Drivers Manual | SNP(4) |
NAME¶
snp — tty snoop interfaceSYNOPSIS¶
#include <sys/snoop.h> intioctl(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 theSNPSTTY
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 byUgen J.S. Antsilevich ⟨ugen@NetVision.net.il⟩.
BUGS¶
This version of snp does not return proper error codes when callingFIONREAD
. It also does not allow
SNPSTTY
to detach itself from the TTY.November 5, 2008 | Debian |