.\"	$OpenBSD: kvm.3,v 1.5 2003/06/02 09:56:20 jmc 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
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.\"    notice, this list of conditions and the following disclaimer in the
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.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. 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.
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.\"     @(#)kvm.3	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.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_close 3 ,
.Xr kvm_getargv 3 ,
.Xr kvm_getenvv 3 ,
.Xr kvm_geterr 3 ,
.Xr kvm_getloadavg 3 ,
.Xr kvm_getprocs 3 ,
.Xr kvm_nlist 3 ,
.Xr kvm_open 3 ,
.Xr kvm_openfiles 3 ,
.Xr kvm_read 3 ,
.Xr kvm_write 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 BSD 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 BSD 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.