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freebsd/share/man/man4/snp.4
Ed Schouten 932ef5b5cd Reintroduce the snp(4) driver.
Because the TTY hooks interface was not finished when I imported the
MPSAFE TTY layer, I had to disconnect the snp(4) driver. This snp(4)
implementation has been sitting in my P4 branch for some time now.
Unfortunately it still doesn't use the same error handling as snp(4)
(returning codes through FIONREAD), but it should already be usable.

I'm committing this to SVN, hoping someone else could polish off its
rough edges. It's always better than having a broken driver sitting in
the tree.
2008-11-05 15:04:03 +00:00

100 lines
1.8 KiB
Groff

.\"
.\" $FreeBSD$
.\"
.Dd November 5, 2008
.Dt SNP 4
.Os
.Sh NAME
.Nm snp
.Nd tty snoop interface
.Sh 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
.Sh DESCRIPTION
.Pa /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
.Cd "device snp" ,
or the
.Nm
module must be loaded,
for these devices to be available.
.Pp
To associate a given
.Nm
device with a tty to be observed, open the
.Nm
device and a tty device, and then issue the
.Dv SNPSTTY
ioctl on
.Nm
device.
The argument passed to the
.Xr ioctl 2
is the address of a variable of type
.Vt int ,
holding the file descriptor of a tty device.
To detach the
.Nm
device from a tty use a pointer to a value of
\-1.
.Pp
The
.Dv SNPGTTY
ioctl returns information about the current tty attached to
the open
.Nm
device.
.Pp
The
.Dv FIONREAD
ioctl returns a positive value equal to the number of characters
in a read buffer.
Special values defined are:
.Bl -tag -width ".Dv SNP_TTYCLOSE"
.It Dv SNP_OFLOW
device overflow occurred, device detached.
.It Dv SNP_TTYCLOSE
tty not attached.
.It Dv SNP_DETACH
.Nm
device has been detached by user or tty device has been closed
and detached.
.El
.Sh SEE ALSO
.Xr pty 4 ,
.Xr sio 4 ,
.Xr kldload 8 ,
.Xr watch 8
.Sh HISTORY
The
.Nm
device first appeared in
.Fx 2.1 .
In
.Fx 8.0
the
.Nm
driver was rewritten to work with the replaced TTY subsystem.
.Sh AUTHORS
The author of the current implementation is
.An Ed Schouten Aq ed@FreeBSD.org .
Previous versions of
.Nm
were based on code written by
.An Ugen J.S. Antsilevich Aq ugen@NetVision.net.il .
.Sh BUGS
This version of
.Nm
does not return proper error codes when calling
.Dv FIONREAD .
It also does not allow
.Dv SNPSTTY
to detach itself from the TTY.