kvm_open(3)

NAME

kvm_open, kvm_openfiles, kvm_close - initialize kernel vir

tual memory
access

LIBRARY

Kernel Data Access Library (libkvm, -lkvm)

SYNOPSIS

#include <fcntl.h>
#include <kvm.h>
kvm_t *
kvm_open(const char *execfile, const char *corefile,
        const   char   *swapfile,   int  flags,  const  char
*errstr);
kvm_t *
kvm_openfiles(const char *execfile, const char *corefile,
        const char *swapfile, int flags, char *errbuf);
int
kvm_close(kvm_t *kd);

DESCRIPTION

The functions kvm_open() and kvm_openfiles() return a de

scriptor used to
access kernel virtual memory via the kvm(3) library rou

tines. Both
active kernels and crash dumps are accessible through this

interface.

The execfile argument is the executable image of the kernel

being examined. This file must contain a symbol table. If this argu

ment is NULL,
the currently running system is assumed, as determined from
getbootfile(3).

The corefile argument is the kernel memory device file. It

can be either
/dev/mem or a crash dump core generated by savecore(8). If

corefile is
NULL, the default indicated by _PATH_MEM from #include

<paths.h>
is used. It can also be set to a special value /dev/null by

utilities
like ps(1) that do not directly access kernel memory.

The swapfile argument is currently unused.

The flags argument indicates read/write access as in open(2)

and applies
only to the core file. Only O_RDONLY, O_WRONLY, and O_RDWR

are permitted.

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 report

ing framework.

The kvm_open() function is the Sun kvm compatible open call.

Here, the
errstr argument indicates how errors should be handled. If

it is NULL,
no errors are reported and the application cannot know the

specific
nature of the failed kvm call. If it is not NULL, errors

are printed to
stderr with errstr prepended to the message, as in per

ror(3). Normally,
the name of the program is used here. The string is assumed

to persist
at least until the corresponding kvm_close() call.

The kvm_openfiles() function provides BSD style error re

porting. Here,
error messages are not printed out by the library. Instead,

the application obtains the error message corresponding to the most re

cent kvm
library call using kvm_geterr() (see kvm_geterr(3)). The

results are
undefined if the most recent kvm call did not produce an er

ror. Since
kvm_geterr() requires a kvm descriptor, but the open rou

tines return NULL
on failure, kvm_geterr() cannot be used to get the error

message if open
fails. Thus, kvm_openfiles() will place any error message

in the errbuf
argument. This buffer should be _POSIX2_LINE_MAX characters

large (from
<limits.h>).

RETURN VALUES

The kvm_open() and kvm_openfiles() functions both return a

descriptor to
be used in all subsequent kvm library calls. The library is

fully reentrant. On failure, NULL is returned, in which case

kvm_openfiles()
writes the error message into errbuf.

The kvm_close() function returns 0 on success and -1 on

failure.

SEE ALSO

open(2), kvm(3), kvm_getargv(3), kvm_getenvv(3),

kvm_geterr(3),
kvm_getprocs(3), kvm_nlist(3), kvm_read(3), kvm_write(3),

kmem(4), mem(4)

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
BSD left little choice.

BSD January 29, 2004

BSD