131 lines
3.8 KiB
Groff
131 lines
3.8 KiB
Groff
.\" Copyright (c) 2008 Yahoo!, Inc.
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.\" All rights reserved.
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.\" Written by: John Baldwin <jhb@FreeBSD.org>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the author nor the names of any co-contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 28, 2010
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.Dt KVM_GETPCPU 3
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.Os
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.Sh NAME
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.Nm kvm_dpcpu_setcpu
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.Nm kvm_getmaxcpu ,
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.Nm kvm_getpcpu
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.Nd access per-CPU data
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.Sh LIBRARY
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.Lb libkvm
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/pcpu.h
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.In sys/sysctl.h
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.In kvm.h
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.Ft int
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.Fn kvm_dpcpu_setcpu "kvm_t *kd" "u_int cpu"
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.Ft int
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.Fn kvm_getmaxcpu "kvm_t *kd"
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.Ft void *
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.Fn kvm_getpcpu "kvm_t *kd" "int cpu"
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.Sh DESCRIPTION
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The
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.Fn kvm_dpcpu_setcpu ,
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.Fn kvm_getmaxcpu ,
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and
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.Fn kvm_getpcpu
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functions are used to access the per-CPU data of active processors in the
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kernel indicated by
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.Fa kd .
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Per-CPU storage comes in two flavours: data stored directly in a
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.Vt "struct pcpu"
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associated with each CPU, and dynamic per-CPU storage (DPCPU), in which a
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single kernel symbol refers to different data depending on what CPU it is
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accessed from.
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.Pp
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The
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.Fn kvm_getmaxcpu
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function returns the maximum number of CPUs supported by the kernel.
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.Pp
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The
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.Fn kvm_getpcpu
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function returns a buffer holding the per-CPU data for a single CPU.
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This buffer is described by the
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.Vt "struct pcpu"
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type.
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The caller is responsible for releasing the buffer via a call to
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.Xr free 3
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when it is no longer needed.
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If
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.Fa cpu
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is not active, then
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.Dv NULL
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is returned instead.
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.Pp
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Symbols for dynamic per-CPU data are accessed via
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.Xr kvm_nlist 3
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as with other symbols.
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.Nm libkvm
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maintains a notion of the "current CPU", set by
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.Xr kvm_dpcpu_setcpu ,
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which defaults to 0.
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Once another CPU is selected,
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.Xr kvm_nlist 3
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will return pointers to that data on the appropriate CPU.
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.Sh CACHING
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.Fn kvm_getmaxcpu
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and
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.Fn kvm_getpcpu
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cache the nlist values for various kernel variables which are
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reused in successive calls.
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You may call either function with
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.Fa kd
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set to
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.Dv NULL
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to clear this cache.
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.Sh RETURN VALUES
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On success, the
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.Fn kvm_getmaxcpu
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function returns the maximum number of CPUs supported by the kernel.
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If an error occurs,
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it returns -1 instead.
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.Pp
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On success, the
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.Fn kvm_getpcpu
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function returns a pointer to an allocated buffer or
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.Dv NULL .
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If an error occurs,
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it returns -1 instead.
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.Pp
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On success, the
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.Fn kvm_dpcpu_setcpu
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call returns 0; if an error occurs, it returns -1 instead.
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.Pp
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If any function encounters an error,
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then an error message may be retrieved via
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.Xr kvm_geterr 3 .
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.Sh SEE ALSO
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.Xr free 3 ,
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.Xr kvm 3
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