freebsd-dev/lib/libkvm/kvm_open.3

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.\" Copyright (c) 1992, 1993
.\" The Regents of the University of California. All rights reserved.
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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
1999-08-28 00:22:10 +00:00
.\" $FreeBSD$
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.\"
.Dd January 29, 2004
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.Dt KVM_OPEN 3
.Os
.Sh NAME
.Nm kvm_open ,
.Nm kvm_openfiles ,
.Nm kvm_close
.Nd initialize kernel virtual memory access
.Sh LIBRARY
.Lb libkvm
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.Sh SYNOPSIS
.In fcntl.h
.In kvm.h
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.Ft kvm_t *
.Fn kvm_open "const char *execfile" "const char *corefile" "const char *swapfile" "int flags" "const char *errstr"
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.Ft kvm_t *
.Fn kvm_openfiles "const char *execfile" "const char *corefile" "const char *swapfile" "int flags" "char *errbuf"
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.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
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through this interface.
.Pp
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The
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.Fa execfile
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argument is the executable image of the kernel being examined.
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This file must contain a symbol table.
If this argument is
.Dv NULL ,
the currently running system is assumed,
as determined from
.Xr getbootfile 3 .
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.Pp
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The
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.Fa corefile
argument 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
from
.In paths.h
is used.
It can also be set to a special value
.Pa /dev/null
by utilities like
.Xr ps 1
that do not directly access kernel memory.
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.Pp
The
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.Fa swapfile
argument is currently unused.
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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.
Only
.Dv O_RDONLY ,
.Dv O_WRONLY ,
and
.Dv O_RDWR
are permitted.
.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
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.Fa errstr
argument indicates how errors should be handled.
If it is
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.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 ,
errors are printed to
.Dv 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
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.Xr kvm_geterr 3 ) .
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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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<limits.h>).
.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 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 ,
.Xr kmem 4 ,
.Xr mem 4
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.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.