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2841e6756d
libvirt was able to set the host_mtu option when an MTU was explicitly given in the interface config (with <mtu size='n'/>), set the MTU of a libvirt network in the network config (with the same named subelement), and would automatically set the MTU of any tap device to the MTU of the network. This patch ties that all together (for networks based on tap devices and either Linux host bridges or OVS bridges) by learning the MTU of the network (i.e. the bridge) during qemuInterfaceBridgeConnect(), and returning that value so that it can then be passed to qemuBuildNicDevStr(); qemuBuildNicDevStr() then sets host_mtu in the interface's commandline options. The result is that a higher MTU for all guests connecting to a particular network will be plumbed top to bottom by simply changing the MTU of the network (in libvirt's config for libvirt-managed networks, or directly on the bridge device for simple host bridges or OVS bridges managed outside of libvirt). One question I have about this - it occurred to me that in the case of migrating a guest from a host with an older libvirt to one with a newer libvirt, the guest may have *not* had the host_mtu option on the older machine, but *will* have it on the newer machine. I'm curious if this could lead to incompatibilities between source and destination (I guess it all depends on whether or not the setting of host_mtu has a practical effect on a guest that is already running - Maxime?) Likewise, we could run into problems when migrating from a newer libvirt to older libvirt - The guest would have been told of the higher MTU on the newer libvirt, then migrated to a host that didn't understand <mtu size='blah'/>. (If this really is a problem, it would be a problem with or without the current patch).
64 lines
2.4 KiB
C
64 lines
2.4 KiB
C
/*
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* qemu_interface.h: QEMU interface management
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*
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* Copyright (C) 2014, 2016 Red Hat, Inc.
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* Copyright IBM Corp. 2014
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see
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* <http://www.gnu.org/licenses/>.
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*
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* Authors:
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* Matthew J. Rosato <mjrosato@linux.vnet.ibm.com>
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*/
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#ifndef __QEMU_INTERFACE_H__
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# define __QEMU_INTERFACE_H__
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# include "domain_conf.h"
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# include "qemu_conf.h"
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# include "qemu_domain.h"
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int qemuInterfaceStartDevice(virDomainNetDefPtr net);
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int qemuInterfaceStartDevices(virDomainDefPtr def);
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int qemuInterfaceStopDevice(virDomainNetDefPtr net);
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int qemuInterfaceStopDevices(virDomainDefPtr def);
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int qemuInterfaceDirectConnect(virDomainDefPtr def,
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virQEMUDriverPtr driver,
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virDomainNetDefPtr net,
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int *tapfd,
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size_t tapfdSize,
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virNetDevVPortProfileOp vmop);
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int qemuInterfaceEthernetConnect(virDomainDefPtr def,
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virQEMUDriverPtr driver,
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virDomainNetDefPtr net,
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int *tapfd,
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size_t tapfdSize);
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int qemuInterfaceBridgeConnect(virDomainDefPtr def,
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virQEMUDriverPtr driver,
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virDomainNetDefPtr net,
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int *tapfd,
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size_t *tapfdSize,
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unsigned int *mtu)
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ATTRIBUTE_NONNULL(2);
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int qemuInterfaceOpenVhostNet(virDomainDefPtr def,
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virDomainNetDefPtr net,
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virQEMUCapsPtr qemuCaps,
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int *vhostfd,
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size_t *vhostfdSize);
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#endif /* __QEMU_INTERFACE_H__ */
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