ccd8bad0bb
(DPCPU): A new API, kvm_dpcpu_setcpu(3), selects the active CPU for the purposes of DPCPU. Calls to kvm_nlist(3) will automatically translate DPCPU symbols and return a pointer to the current CPU's version of the data. Consumers needing to read the same symbol on several CPUs will invoke a series of setcpu/nlist calls, one per CPU of interest. This addition makes it possible for tools like netstat(1) to query the values of DPCPU variables during crashdump analysis, and is based on similar code handling virtualized global variables. MFC after: 1 week Sponsored by: Juniper Networks, Inc.
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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.Vn 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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