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