1.\" Copyright (c) 1992, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software developed by the Computer Systems 5.\" Engineering group at Lawrence Berkeley Laboratory under DARPA contract 6.\" BG 91-66 and contributed to Berkeley. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" @(#)kvm_read.3 8.1 (Berkeley) 6/4/93 37.\" $FreeBSD: src/lib/libkvm/kvm_read.3,v 1.6.2.3 2001/12/17 10:08:30 ru Exp $ 38.\" $DragonFly: src/lib/libkvm/kvm_read.3,v 1.3 2006/01/11 01:12:59 corecode Exp $ 39.\" 40.Dd January 8, 2006 41.Dt KVM_READ 3 42.Os 43.Sh NAME 44.Nm kvm_read , 45.Nm kvm_write 46.Nd read or write kernel virtual memory 47.Sh LIBRARY 48.Lb libkvm 49.Sh SYNOPSIS 50.In kvm.h 51.Ft ssize_t 52.Fn kvm_read "kvm_t *kd" "unsigned long addr" "void *buf" "size_t nbytes" 53.Ft "char *" 54.Fn kvm_readstr "kvm_t *kd" "unsigned long addr" "char *buf" "size_t *len" 55.Ft ssize_t 56.Fn kvm_write "kvm_t *kd" "unsigned long addr" "const void *buf" "size_t nbytes" 57.Sh DESCRIPTION 58The 59.Fn kvm_read , 60.Fn kvm_readstr 61and 62.Fn kvm_write 63functions are used to read and write kernel virtual memory (or a crash 64dump file). See 65.Fn kvm_open 3 66or 67.Fn kvm_openfiles 3 68for information regarding opening kernel virtual memory and crash dumps. 69.Pp 70The 71.Fn kvm_read 72function transfers 73.Fa nbytes 74bytes of data from 75the kernel space address 76.Fa addr 77to 78.Fa buf . 79Conversely, 80.Fn kvm_write 81transfers data from 82.Fa buf 83to 84.Fa addr . 85Unlike their SunOS counterparts, these functions cannot be used to 86read or write process address spaces. 87.Pp 88The 89.Fn kvm_readstr 90function exists for convenience to read NUL terminated strings 91from the kernel address space. 92If 93.Fa buf 94is 95.Dv NULL , 96.Fn kvm_readstr 97will allocate a sufficiently large buffer, which needs to be 98deallocated via 99.Xr free 3 100by the caller. 101If 102.Fa len 103is not 104.Dv NULL , 105.Fn kvm_readstr 106will interpret the value it is pointing to as the size of 107.Fa buf 108and will store the size of the complete string at 109.Fa addr . 110Note that if only 111.Fa buf 112is too small to hold the complete string, 113.Fn kvm_readstr 114will return 115.Dv NULL 116but set 117.Fa len 118to the size needed. 119.Sh RETURN VALUES 120For 121.Fn kvm_read 122and 123.Fn kvm_write 124the number of bytes actually transferred is returned, if the request 125was successful. 126Otherwise, -1 is returned. 127.Pp 128For 129.Fn kvm_readstr 130.Dv NULL 131is returned on failure. 132Upon success, the address of the string is returned, which will be 133.Fa buf 134if this was supplied. 135.Sh SEE ALSO 136.Xr kvm 3 , 137.Xr kvm_close 3 , 138.Xr kvm_getargv 3 , 139.Xr kvm_getenvv 3 , 140.Xr kvm_geterr 3 , 141.Xr kvm_getprocs 3 , 142.Xr kvm_nlist 3 , 143.Xr kvm_open 3 , 144.Xr kvm_openfiles 3 145