KVM_OPEN(3KVM) Kernel VM Library Functions KVM_OPEN(3KVM)

NAME

kvm_open, kvm_close - specify a kernel to examine

SYNOPSIS

cc [ flag... ] file... -lkvm [ library...]
#include <kvm.h>
#include <fcntl.h>

kvm_t *kvm_open(char *namelist, char *corefile, char *swapfile, int flag,
char *errstr);


int kvm_close(kvm_t *kd);

DESCRIPTION

The kvm_open() function initializes a set of file descriptors to be
used in subsequent calls to kernel virtual memory ( VM) routines. It
returns a pointer to a kernel identifier that must be used as the kd
argument in subsequent kernel VM function calls.


The namelist argument specifies an unstripped executable file whose
symbol table will be used to locate various offsets in corefile. If
namelist is NULL, the symbol table of the currently running kernel is
used to determine offsets in the core image. In this case, it is up
to the implementation to select an appropriate way to resolve
symbolic references, for instance, using /dev/ksyms as a default
namelist file.


The corefile argument specifies a file that contains an image of
physical memory, for instance, a kernel crash dump file (see
savecore(8)) or the special device /dev/mem. If corefile is NULL, the
currently running kernel is accessed, using /dev/mem and /dev/kmem.


The swapfile argument specifies a file that represents the swap
device. If both corefile and swapfile are NULL, the swap device of
the currently running kernel is accessed. Otherwise, if swapfile is
NULL, kvm_open() may succeed but subsequent kvm_getu(3KVM) function
calls may fail if the desired information is swapped out.


The flag function is used to specify read or write access for
corefile and may have one of the following values:

O_RDONLY
open for reading


O_RDWR
open for reading and writing


The errstr argument is used to control error reporting. If it is a
null pointer, no error messages will be printed. If it is non-null,
it is assumed to be the address of a string that will be used to
prefix error messages generated by kvm_open. Errors are printed to
stderr. A useful value to supply for errstr would be argv[0]. This
has the effect of printing the process name in front of any error
messages.


Applications using libkvm are dependent on the underlying data model
of the kernel image, that is, whether it is a 32-bit or 64-bit
kernel.


The data model of these applications must match the data model of the
kernel in order to correctly interpret the size and offsets of kernel
data structures. For example, a 32-bit application that uses the
32-bit version of the libkvm interfaces will fail to open a 64-bit
kernel image. Similarly, a 64-bit application that uses the 64-bit
version of the libkvm interfaces will fail to open a 32-bit kernel
image.


The kvm_close() function closes all file descriptors that were
associated with kd. These files are also closed on exit(2) and
execve() (see exec(2)). kvm_close() also resets the proc pointer
associated with kvm_nextproc(3KVM) and flushes any cached kernel
data.

RETURN VALUES

The kvm_open() function returns a non-null value suitable for use
with subsequent kernel VM function calls. On failure, it returns NULL
and no files are opened.


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

FILES

/dev/kmem


/dev/ksyms


/dev/mem

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Stable |
+--------------------+-----------------+
|MT-Level | Unsafe |
+--------------------+-----------------+

SEE ALSO

exec(2), exit(2), pathconf(2), getloadavg(3C), sysconf(3C),
kstat(3KSTAT), kvm_getu(3KVM), kvm_kread(3KVM), kvm_nextproc(3KVM),
kvm_nlist(3KVM), libkvm(3LIB), proc(5), attributes(7), lfcompile(7),
savecore(8)

NOTES

Kernel core dumps should be examined on the platform on which they
were created. While a 32-bit application running on a 64-bit kernel
can examine a 32-bit core dump, a 64-bit application running on a
64-bit kernel cannot examine a kernel core dump from the 32-bit
system.


On 32-bit systems, applications that use libkvm to access the running
kernel must be 32-bit applications. On systems that support both
32-bit and 64-bit applications, applications that use the libkvm
interfaces to access the running kernel must themselves be 64-bit
applications.


Although the libkvm API is Stable, the symbol names and data values
that can be accessed through this set of interfaces are Private and
are subject to ongoing change.


Applications using libkvm are likely to be platform- and release-
dependent.


Most of the traditional uses of libkvm have been superseded by more
stable interfaces that allow the same information to be extracted
more efficiently, yet independent of the kernel data model. For
examples, see sysconf(3C), proc(5), kstat(3KSTAT), getloadavg(3C),
and pathconf(2).

May 2, 2002 KVM_OPEN(3KVM)