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(1M)) 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(5) for descriptions of the following attributes:


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

SEE ALSO


savecore(1M), exec(2), exit(2), pathconf(2), getloadavg(3C),
kstat(3KSTAT), kvm_getu(3KVM), kvm_nextproc(3KVM), kvm_nlist(3KVM),
kvm_kread(3KVM), libkvm(3LIB), sysconf(3C), proc(4), attributes(5),
lfcompile(5)

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(4), kstat(3KSTAT), getloadavg(3C), and pathconf(2).


May 2, 2002 KVM_OPEN(3KVM)