SNP(4) | Device Drivers 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 withdevice 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¶
Thesnp
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 ofsnp
were based on code written by
Ugen J.S. Antsilevich ⟨ugen@NetVision.net.il⟩.
BUGS¶
This version ofsnp
does not return proper
error codes when calling FIONREAD
. It also
does not allow SNPSTTY
to detach itself
from the TTY.November 5, 2008 | Debian |