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KVM_GETPCPU(3) FreeBSD Library Functions Manual KVM_GETPCPU(3)
NAME
kvm_dpcpu_setcpu, kvm_getmaxcpu, kvm_getpcpu - access per-CPU data
LIBRARY
Kernel Data Access Library (libkvm, -lkvm)
SYNOPSIS
#include <sys/param.h>
#include <sys/pcpu.h>
#include <sys/sysctl.h>
#include <kvm.h>
int
kvm_dpcpu_setcpu(kvm_t *kd, u_int cpu);
int
kvm_getmaxcpu(kvm_t *kd);
int
kvm_getncpus(kvm_t *kd);
void *
kvm_getpcpu(kvm_t *kd, int cpu);
ssize_t
kvm_read_zpcpu(kvm_t *kd, u_long base, void *buf, size_t size, int cpu);
uint64_t
kvm_counter_u64_fetch(kvm_t *kd, u_long base);
DESCRIPTION
The kvm_dpcpu_setcpu(), kvm_getmaxcpu(), and kvm_getpcpu() functions are
used to access the per-CPU data of active processors in the kernel
indicated by kd. Per-CPU storage comes in two flavours: data stored
directly in a struct pcpu associated with each CPU, and dynamic per-CPU
storage (DPCPU), in which a single kernel symbol refers to different data
depending on what CPU it is accessed from.
The kvm_getmaxcpu() function returns the maximum number of CPUs supported
by the kernel.
The kvm_getncpus() function returns the current number of CPUs in the
kernel.
The kvm_getpcpu() function returns a buffer holding the per-CPU data for
a single CPU. This buffer is described by the struct pcpu type. The
caller is responsible for releasing the buffer via a call to free(3) when
it is no longer needed. If cpu is not active, then NULL is returned
instead.
The kvm_read_zpcpu() function is used to obtain private per-CPU copy from
a UMA_ZONE_PCPU zone(9). It takes base argument as base address of an
allocation and copyies size bytes into buf from the part of allocation
that is private to cpu.
The kvm_counter_u64_fetch() function fetches value of a counter(9)
pointed by base address.
kvm_getmaxcpu() and kvm_getpcpu() cache the nlist values for various
kernel variables which are reused in successive calls. You may call
either function with kd set to NULL to clear this cache.
RETURN VALUES
On success, the kvm_getmaxcpu() function returns the maximum number of
CPUs supported by the kernel. If an error occurs, it returns -1 instead.
On success, the kvm_getpcpu() function returns a pointer to an allocated
buffer or NULL. If an error occurs, it returns -1 instead.
On success, the kvm_dpcpu_setcpu() call returns 0; if an error occurs, it
returns -1 instead.
On success, the kvm_read_zpcpu() function returns number of bytes copied.
If an error occurs, it returns -1 instead.
If any function encounters an error, then an error message may be
retrieved via kvm_geterr(3).
SEE ALSO
free(3), kvm(3), counter(9), zone(9)
FreeBSD 14.0-RELEASE-p11 March 15, 2017 FreeBSD 14.0-RELEASE-p11