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man pages section 3: Extended Library Functions, Volume 2

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Updated: Thursday, June 13, 2019
 
 

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. If corefile contains pointers to files holding additional sections of memory and the files are present in the same directory as corefile, they will be loaded and appended automatically to the image unless the KVM_NSRCH flag is set. If the KVM_NSRCH flag is set and some of the files referenced by corefile is missing, kvm_open() will load accessible files and return pointer to kvm_t.

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

KVM_NSRCH

do not perform the search for additional sections

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
Committed
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 Committed, 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 pathconf(2), sysconf(3C), kstat(3KSTAT), getloadavg(3C), and proc(5).