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\"     @(#)kvm_open.3   8.3 (Berkeley) 4/19/94
\"
Dd September 14, 2011
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
Sh SYNOPSIS
In fcntl.h
In kvm.h
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
and
Fn kvm_openfiles
return a descriptor used to access kernel virtual memory
via the
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; in this case, the functions will
attempt to use the
Xr ksyms 4
device indicated by
Dv _PATH_KSYMS
in
In paths.h ;
if that fails, then they will use the file indicated by the
Xr sysctl 3
variable
Va machdep.booted_kernel ,
or (if the sysctl information is not available)
the default kernel path indicated by
Dv _PATH_UNIX
in
In paths.h .
Pp
Fa corefile
is the kernel memory device file.
It can be either
Pa /dev/mem
or a crash dump core generated by
Xr savecore 8 .
If
Fa corefile
is
Dv NULL ,
the default indicated by
Dv _PATH_MEM
from
In paths.h
is used.
Pp
Fa swapfile
should indicate the swap device.
If
Dv NULL ,
Dv _PATH_DRUM
from
In paths.h
is used.
Pp
The
Fa flags
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
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 initialize 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 .
Pp
There are two open routines which differ only with respect to
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 ,
no errors are reported and the application cannot know the
specific nature of the failed kvm call.
If it is not
Dv NULL ,
errors are printed to stderr with
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.
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
In limits.h ) .
Sh RETURN VALUES
The
Fn kvm_open
and
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
writes the error message into
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_getkernelname 3 ,
Xr kvm_getprocs 3 ,
Xr kvm_nlist 3 ,
Xr kvm_read 3 ,
Xr kvm_write 3
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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