.\"	$OpenBSD: kvm.3,v 1.10 2020/06/25 12:20:17 kn Exp $
.\"	$NetBSD: kvm.3,v 1.2 1996/03/18 22:33:11 thorpej Exp $
.\"
.\" Copyright (c) 1992, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software developed by the Computer Systems
.\" Engineering group at Lawrence Berkeley Laboratory under DARPA contract
.\" BG 91-66 and contributed to Berkeley.
.\"
.\" 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.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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.
.\"
.\"     @(#)kvm.3	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: June 25 2020 $
.Dt KVM 3
.Os
.Sh NAME
.Nm kvm
.Nd kernel memory interface
.Sh DESCRIPTION
The
.Nm kvm
library provides a uniform interface for accessing kernel virtual memory
images, including live systems and crash dumps.
Access to live systems is via
.Pa /dev/mem
while crash dumps can be examined via the core file generated by
.Xr savecore 8 .
The interface behaves identically in both cases.
Memory can be read and written, kernel symbol addresses can be
looked up efficiently, and information about user processes can
be gathered.
.Pp
.Fn kvm_open
is first called to obtain a descriptor for all subsequent calls.
.Sh FILES
.Bl -tag -width /dev/mem -compact
.It Pa /dev/mem
interface to physical memory
.El
.Sh SEE ALSO
.Xr kvm_dump 3 ,
.Xr kvm_geterr 3 ,
.Xr kvm_getfiles 3 ,
.Xr kvm_getloadavg 3 ,
.Xr kvm_getprocs 3 ,
.Xr kvm_nlist 3 ,
.Xr kvm_open 3 ,
.Xr kvm_read 3
.Sh STANDARDS
The kvm interface was first introduced in SunOS.
A considerable
number of programs have been developed that use this interface,
making backward compatibility highly desirable.
In most respects, the Sun kvm interface is consistent and clean.
Accordingly, the generic portion of the interface (i.e.,
.Fn kvm_open ,
.Fn kvm_close ,
.Fn kvm_read ,
.Fn kvm_write ,
and
.Fn kvm_nlist )
has been incorporated into the
.Bx
interface.
Indeed, many kvm
applications (i.e., debuggers and statistical monitors) use only
this subset of the interface.
.Pp
The process interface was not kept.
This is not a portability
issue since any code that manipulates processes is inherently
machine dependent.
.Pp
Finally, the Sun kvm error reporting semantics are poorly defined.
The library can be configured either to print errors to stderr automatically,
or to print no error messages at all.
In the latter case, the nature of the error cannot be determined.
To overcome this, the
.Bx
interface includes a
routine,
.Xr kvm_geterr 3 ,
to return (not print out) the error message
corresponding to the most recent error condition on the
given descriptor.