NAME
kvm_open, kvm_close − specify a kernel to examine
SYNOPSIS
#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
kvm_open()
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.
kvm_close()
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 −1 on failure.
FILES
/dev/kmem
/dev/ksyms
/dev/mem
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
SEE ALSO
savecore(1M), exec(2), exit(2), pathconf(2), getloadavg(3C), kstat(3KSTAT), kvm_getu(3KVM), kvm_nextproc(3KVM), kvm_nlist(3KVM), kvm_read(3KVM), sysconf(3C), libkvm(3LIB), 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.
Applications using libkvm are likely to be platform- and release-dependent.
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.
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).