freebsd-dev/share/man/man4/snp.4

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.\"
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.\" $FreeBSD$
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.\"
.Dd September 18, 2005
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.Dt SNP 4
.Os
.Sh NAME
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.Nm snp
.Nd tty snoop interface
.Sh SYNOPSIS
.In sys/snoop.h
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.Ft int
.Fn ioctl fd SNPSTTY &dev
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.Ft int
.Fn ioctl fd SNPGTTY &dev
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.Ft int
.Fn ioctl fd FIONREAD &result
.Sh DESCRIPTION
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.Pa /dev/snp?
are snoop devices which allow users to attach to any tty
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and watch activities on it.
The kernel must be compiled with
.Cd "device snp" ,
or the
.Nm
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module must be loaded,
for these devices to be available.
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.Pp
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To associate a given
.Nm
device with a tty to be observed, open the
.Nm
device and a tty device, and then issue the
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.Dv SNPSTTY
ioctl on
.Nm
device.
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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.
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To detach the
.Nm
device from a tty use a pointer to a value of
\-1.
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.Pp
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The
.Dv SNPGTTY
ioctl returns information about the current tty attached to
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the open
.Nm
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device.
.Pp
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The
.Dv FIONREAD
ioctl returns a positive value equal to the number of characters
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in a read buffer.
Special values defined are:
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.Bl -tag -width ".Dv SNP_TTYCLOSE"
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.It Dv SNP_OFLOW
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device overflow occurred, device detached.
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.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.
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.El
.Sh SEE ALSO
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.Xr pty 4 ,
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.Xr sio 4 ,
.Xr kldload 8 ,
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.Xr watch 8
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.Sh HISTORY
The
.Nm
device first appeared in
.Fx 2.1 .
.Sh AUTHORS
.An Ugen J.S. Antsilevich Aq ugen@NetVision.net.il
.Sh BUGS
Caveat emptor!
This manual page is horribly stale and wildly inaccurate in some places.
.Pp
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While in line mode, user input cannot be seen.
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No signals may be sent to the observed tty.