81 lines
1.8 KiB
Groff
81 lines
1.8 KiB
Groff
.\"
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.\" @(#)snp.4 1.1 (FreeBSD) 2/17/95
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.\"
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.Dd February 17, 1995
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.Dt SNP 4
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.Os FreeBSD
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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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.Fd #include <sys/ioctl.h>
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.Fd #include <sys/snoop.h>
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.Ft int
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.Fn ioctl fd SNPSTTY &snptty
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.Ft int
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.Fn ioctl fd SNPGTTY &snptty
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.Ft int
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.Fn ioctl fd FIONREAD 0
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.Sh DESCRIPTION
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/dev/snp? are snoop devices which allow user to attach to any tty
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and watch activities on it.
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To associate a given
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.Nm snp
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device with a tty to be observed, open the
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.Nm snp
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device and then use the SNPSTTY ioctl.
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The argument passed to the IOCTL is the address of a structure of
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the following type:
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.Bd -literal -ffset indent
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struct snptty {
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int st_unit; /* number of the tty unit */
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int st_type; /* type of the tty to attach */
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#define ST_PTY 0 /* regular pty */
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#define ST_VTY 1 /* syscons vty */
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#define ST_SIO 2 /* serial lines */
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}
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.Ed
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.Pp
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By setting st_type or st_unit to -1, the user may detach the snp device
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for a tty.
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.Pp
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The SNPGTTY ioctl returns information about the current tty attached to
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the open
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.Nm snp
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device.
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.Pp
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The FIONREAD 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 SNP_TTYCLOSE
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.It Dv SNP_OFLOW
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device overflow occured, device detatched.
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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 snp
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device has been detatched by user or tty device has been closed
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and detatched.
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.Sh SEE ALSO
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.Xr watch 8 ,
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.Xr pty 4 ,
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.Xr sio 4
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.Sh RESTRICTIONS
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Only the superuser may access the
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.Nm snp
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devices.
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.Sh BUGS
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While in line mode, user input can't be seen.
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.Nm
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snp
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is a read-only device, there is no ability to write to attached tty device.
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.Sh AUTHOR
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Ugen J.S. Antsilevich <ugen@NetVision.net.il>
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.Sh HISTORY
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The
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.Nm
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snp
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device first appeared in FreeBSD 2.1.
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