NetBSD/lib/libkvm/kvm_open.3

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.\" $NetBSD: kvm_open.3,v 1.7 2000/06/13 15:48:57 simonb Exp $
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.\"
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.\" Copyright (c) 1992, 1993
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.\"
.\" 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.
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.\" @(#)kvm_open.3 8.3 (Berkeley) 4/19/94
.\"
.Dd April 19, 1994
.Dt KVM_OPEN 3
.Os
.Sh NAME
.Nm kvm_open ,
.Nm kvm_openfiles ,
.Nm kvm_close
.Nd initialize kernel virtual memory access
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.Sh LIBRARY
.Lb libkvm
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.Sh SYNOPSIS
.Fd #include <fcntl.h>
.Fd #include <kvm.h>
.br
.Ft kvm_t *
.Fn kvm_open "const char *execfile" "const char *corefile" "char *swapfile" "int flags" "const char *errstr"
.Ft kvm_t *
.Fn kvm_openfiles "const char *execfile" "const char *corefile" "char *swapfile" "int flags" "char *errbuf"
.Ft int
.Fn kvm_close "kvm_t *kd"
.Sh DESCRIPTION
The functions
.Fn kvm_open
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and
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.Fn kvm_openfiles
return a descriptor used to access kernel virtual memory
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via the
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.Xr kvm 3
library routines. Both active kernels and crash dumps are accessible
through this interface.
.Pp
.Fa execfile
is the executable image of the kernel being examined.
This file must contain a symbol table.
If this argument is
.Dv NULL ,
the currently running system is assumed,
which is indicated by
.Dv _PATH_UNIX
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in
.Pa Aq paths.h .
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.Pp
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.Fa corefile
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is the kernel memory device file. It can be either
.Pa /dev/mem
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or a crash dump core generated by
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.Xr savecore 8 .
If
.Fa corefile
is
.Dv NULL ,
the default indicated by
.Dv _PATH_MEM
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from
.Pa Aq paths.h
is used.
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.Pp
.Fa swapfile
should indicate the swap device. If
.Dv NULL ,
.Dv _PATH_DRUM
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from
.Pa Aq paths.h
is used.
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.Pp
The
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.Fa flags
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argument indicates read/write access as in
.Xr open 2
and applies only to the core file.
The only permitted flags from
.Xr open 2
are
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.Dv O_RDONLY ,
.Dv O_WRONLY ,
and
.Dv O_RDWR .
.Pp
As a special case, a
.Fa flags
argument of
.Dv KVM_NO_FILES
will initialse the
.Xr kvm 3
library for use on active kernels only using
.Xr sysctl 3
for retrieving kernel data and ignores the
.Fa execfile ,
.Fa corefile
and
.Fa swapfile
arguments. Only a small subset of the
.Xr kvm 3
library functions are available using this method. These
are currently
.Xr kvm_getproc2 3 ,
.Xr kvm_getargv2 3
and
.Xr kvm_getenvv2 3 .
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.Pp
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There are two open routines which differ only with respect to
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the error mechanism.
One provides backward compatibility with the SunOS kvm library, while the
other provides an improved error reporting framework.
.Pp
The
.Fn kvm_open
function is the Sun kvm compatible open call. Here, the
.Fa errstr
argument indicates how errors should be handled. If it is
.Dv NULL ,
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no errors are reported and the application cannot know the
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specific nature of the failed kvm call.
If it is not
.Dv NULL ,
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errors are printed to stderr with
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.Fa errstr
prepended to the message, as in
.Xr perror 3 .
Normally, the name of the program is used here.
The string is assumed to persist at least until the corresponding
.Fn kvm_close
call.
.Pp
The
.Fn kvm_openfiles
function provides
.Bx
style error reporting.
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Here, error messages are not printed out by the library.
Instead, the application obtains the error message
corresponding to the most recent kvm library call using
.Fn kvm_geterr
(see
.Xr kvm_geterr 3 ).
The results are undefined if the most recent kvm call did not produce
an error.
Since
.Fn kvm_geterr
requires a kvm descriptor, but the open routines return
.Dv NULL
on failure,
.Fn kvm_geterr
cannot be used to get the error message if open fails.
Thus,
.Fn kvm_openfiles
will place any error message in the
.Fa errbuf
argument. This buffer should be _POSIX2_LINE_MAX characters large (from
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.Pa Aq limits.h ) .
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.Sh RETURN VALUES
The
.Fn kvm_open
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and
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.Fn kvm_openfiles
functions both return a descriptor to be used
in all subsequent kvm library calls.
The library is fully re-entrant.
On failure,
.Dv NULL
is returned, in which case
.Fn kvm_openfiles
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writes the error message into
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.Fa errbuf .
.Pp
The
.Fn kvm_close
function returns 0 on success and -1 on failure.
.Sh BUGS
There should not be two open calls. The ill-defined error semantics
of the Sun library and the desire to have a backward-compatible library
for
.Bx
left little choice.
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.Sh SEE ALSO
.Xr open 2 ,
.Xr kvm 3 ,
.Xr kvm_getargv 3 ,
.Xr kvm_getenvv 3 ,
.Xr kvm_geterr 3 ,
.Xr kvm_getprocs 3 ,
.Xr kvm_nlist 3 ,
.Xr kvm_read 3 ,
.Xr kvm_write 3