87 lines
2.8 KiB
Groff
87 lines
2.8 KiB
Groff
.\" $NetBSD: viomb.4,v 1.4 2020/08/24 19:27:36 ryoon Exp $
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.\"
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.\" Copyright (C) 2011 Minoura Makoto.
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.\" All rights reserved.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" 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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.Dd August 25, 2020
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.Dt VIOMB 4
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.Os
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.Sh NAME
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.Nm viomb
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.Nd VirtIO memory ballooning driver
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.Sh SYNOPSIS
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.Cd "virtio* at pci? dev ? function ?"
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.Cd "viomb* at virtio?"
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.Sh DESCRIPTION
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.Xr virtio 4
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defines an interface for efficient, standard, and extensible I/O between
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the hypervisor and the virtual machine.
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The
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.Nm
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driver supports the virtio-compliant memory ballooning device.
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.Pp
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Memory ballooning works as follows:
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.Pp
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.Bl -enum -compact
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.It
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The host operator requests a guest to return some amount of memory to the host
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(via e.g. Qemu monitor balloon command).
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.It
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The hypervisor sends the request via VirtIO memory ballooning device.
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.It
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The guest
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.Nm
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driver requests allocation of that amount of physical memory from the
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.Nx
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memory management system.
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.It
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The
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.Nm
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device tells the hypervisor the guest physical memory address of the
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allocated memory via VirtIO memory ballooning device.
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.El
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.Pp
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The sysctl node
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.Li hw.viomb.npages
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shows the requested number of memory pages to return to the hypervisor, while
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.Li hw.viomb.actual
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shows the actual number of memory pages that are already returned to the hypervisor.
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.Sh SEE ALSO
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.Xr virtio 4 ,
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.Xr sysctl 8 ,
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.Xr x86/balloon 4
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.Pp
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.Rs
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.%A Rusty Russell, IBM Corporation
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.%T Virtio PCI Card Specification
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.%U http://ozlabs.org/~rusty/virtio-spec/
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.Re
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.Sh HISTORY
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The
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.Nm
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device driver appeared in
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.Nx 6.0 .
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.Sh BUGS
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The userland interface should be same as the Xen ballooning device.
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