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 1.4 2008/09/07 08:36:54 swildner Exp $ 39.\" 40.Dd January 8, 2006 41.Dt KVM_READ 3 42.Os 43.Sh NAME 44.Nm kvm_read , 45.Nm kvm_readstr , 46.Nm kvm_write 47.Nd read or write kernel virtual memory 48.Sh LIBRARY 49.Lb libkvm 50.Sh SYNOPSIS 51.In kvm.h 52.Ft ssize_t 53.Fn kvm_read "kvm_t *kd" "unsigned long addr" "void *buf" "size_t nbytes" 54.Ft "char *" 55.Fn kvm_readstr "kvm_t *kd" "unsigned long addr" "char *buf" "size_t *len" 56.Ft ssize_t 57.Fn kvm_write "kvm_t *kd" "unsigned long addr" "const void *buf" "size_t nbytes" 58.Sh DESCRIPTION 59The 60.Fn kvm_read , 61.Fn kvm_readstr 62and 63.Fn kvm_write 64functions are used to read and write kernel virtual memory (or a crash 65dump file). See 66.Fn kvm_open 3 67or 68.Fn kvm_openfiles 3 69for information regarding opening kernel virtual memory and crash dumps. 70.Pp 71The 72.Fn kvm_read 73function transfers 74.Fa nbytes 75bytes of data from 76the kernel space address 77.Fa addr 78to 79.Fa buf . 80Conversely, 81.Fn kvm_write 82transfers data from 83.Fa buf 84to 85.Fa addr . 86Unlike their SunOS counterparts, these functions cannot be used to 87read or write process address spaces. 88.Pp 89The 90.Fn kvm_readstr 91function exists for convenience to read NUL terminated strings 92from the kernel address space. 93If 94.Fa buf 95is 96.Dv NULL , 97.Fn kvm_readstr 98will allocate a sufficiently large buffer, which needs to be 99deallocated via 100.Xr free 3 101by the caller. 102If 103.Fa len 104is not 105.Dv NULL , 106.Fn kvm_readstr 107will interpret the value it is pointing to as the size of 108.Fa buf 109and will store the size of the complete string at 110.Fa addr . 111Note that if only 112.Fa buf 113is too small to hold the complete string, 114.Fn kvm_readstr 115will return 116.Dv NULL 117but set 118.Fa len 119to the size needed. 120.Sh RETURN VALUES 121For 122.Fn kvm_read 123and 124.Fn kvm_write 125the number of bytes actually transferred is returned, if the request 126was successful. 127Otherwise, -1 is returned. 128.Pp 129For 130.Fn kvm_readstr 131.Dv NULL 132is returned on failure. 133Upon success, the address of the string is returned, which will be 134.Fa buf 135if this was supplied. 136.Sh SEE ALSO 137.Xr kvm 3 , 138.Xr kvm_close 3 , 139.Xr kvm_getargv 3 , 140.Xr kvm_getenvv 3 , 141.Xr kvm_geterr 3 , 142.Xr kvm_getprocs 3 , 143.Xr kvm_nlist 3 , 144.Xr kvm_open 3 , 145.Xr kvm_openfiles 3 146