Document a few kernel functions and the sysctl tunables that

affect their behaviour.

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+.\"
+.\" Copyright (c) 2003 Joseph Koshy <jkoshy@freebsd.org>
+.\"
+.\" All rights reserved.
+.\"
+.\" This program is free software.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.Dd November 11, 2003
+.Os
+.Dt p_candebug 9
+.Sh NAME
+.Nm p_candebug
+.Nd determine debuggability of a process
+.Sh SYNOPSIS
+.In sys/proc.h
+.Ft int
+.Fn p_candebug "struct thread *td" "struct proc *p"
+.Sh DESCRIPTION
+This function can be used to determine if a given process
+.Fa p
+is debuggable by the thread
+.Fa td .
+.Sh SYSCTL TUNABLES
+The following
+.Xr sysctl 8
+tunables directly influence the behaviour of
+.Fn p_candebug :
+.Bl -tag -width indent
+.It Va kern.securelevel
+debugging of the init process is not allowed if this tunable is
+.Li 1
+or greater.
+.It Va security.bsd.unprivileged_proc_debug
+must be set to a non-zero value to allow unprivileged processes
+access to the kernel's debug facilities.
+.El
+.Sh RETURN VALUES
+.Fn p_candebug
+returns
+.Li 0
+if the process denoted by
+.Ar p
+is debuggable by thread
+.Ar td ,
+or a non-zero error return value otherwise.
+.Sh ERRORS
+.Bl -tag -width Er
+.It Bq Er EACCESS
+The MAC subsystem denied debuggability.
+.It Bq Er EAGAIN
+Process
+.Fa p
+is in the process of being
+.Fn exec Ns 'ed.
+.It Bq Er EPERM
+Thread
+.Fa td
+lacks super-user credentials and process
+.Fa p
+is executing a set-user-id or set-group-id executable.
+.It Bq Er EPERM
+Thread
+.Fa td
+lacks super-user credentials and process
+.Fa p Ns 's
+group set is not a subset of
+.Fa td Ns 's
+effective group set.
+.It Bq Er EPERM
+Thread
+.Fa td
+lacks super-user credentials and process
+.Fa p Ns 's
+user ids do not match thread
+.Fa td Ns 's
+effective user id.
+.It Bq Er EPERM
+Process
+.Fa p
+denotes the initial process
+.Fn initproc
+and the sysctl tunable
+.Va kern.securelevel
+is greater than zero.
+.It Bq Er ESRCH
+Process
+.Fa p
+is not visible to thread
+.Fa td
+as determined by
+.Xr cr_seeotheruids 9
+or
+.Xr cr_seeothergids 9 .
+.It Bq Er ESRCH
+Thread
+.Fa td
+has been jailed and process
+.Fa p
+does not belong to the same jail as
+.Fa td .
+.It Bq Er ESRCH
+The MAC subsystem denied debuggability.
+.El
+.Sh SEE ALSO
+.Xr intro 2 ,
+.Xr jail 2 ,
+.Xr sysctl 8 ,
+.Xr cr_seeotheruids 9 ,
+.Xr cr_seeothergids 9 ,
+.Xr mac 9 ,
+.Xr prison_check 9