OpenBSD manual page server

Manual Page Search Parameters

KVM_OPEN(3) Library Functions Manual KVM_OPEN(3)

kvm_open, kvm_openfiles, kvm_closeinitialize kernel virtual memory access

#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);

kvm_close(kvm_t *kd);

The functions () and kvm_openfiles() return a descriptor used to access kernel virtual memory via the kvm(3) library routines. Both active kernels and crash dumps are accessible through this interface.

execfile is the executable image of the kernel being examined. This file must contain a symbol table. If this argument is NULL, the currently running system is assumed, which is indicated by _PATH_KSYMS, if it exists, otherwise _PATH_UNIX is used. Both are defined in <paths.h>.

corefile 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 <paths.h> is used.

swapfile should indicate the swap device. If NULL, no swap device will be used.

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. A special value KVM_NO_FILES can be specified which will cause no files to be opened and the handle can only be used on live kernels on a limited subset of all kvm operations.

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 reporting framework.

The () 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 perror(3). Normally, the name of the program is used here. The string is assumed to persist at least until the corresponding () call.

The () function provides BSD style error reporting. Here, error messages are not printed out by the library. Instead, the application obtains the error message corresponding to the most recent kvm library call using () (see kvm_geterr(3)). The results are undefined if the most recent kvm call did not produce an error. Since kvm_geterr() requires a kvm descriptor, but the open routines 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>).

The kvm_open() and kvm_openfiles() functions both return a descriptor to be used in all subsequent kvm library calls. The library is fully re-entrant. 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.

open(2), kvm(3), kvm_geterr(3), kvm_getprocs(3), kvm_nlist(3), kvm_read(3)

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.

April 4, 2015 OpenBSD-current