Example: <network> ... <mtu size='9000'/> ... If mtu is unset, it's assumed that we want the default for whatever is the underlying transport (usually this is 1500). This setting isn't yet wired in, so it will have no effect. This partially resolves: https://bugzilla.redhat.com/1224348 --- Change from V1: * switch from <bridge .... mtu='9000'/> to <mtu size='9000'/> for consistency and to allow for potentially setting an MTU on a network that doesn't have a <bridge> element. * use Michal's mtu element definition from networkcommon.rng rather than rolling my own. docs/formatnetwork.html.in | 19 ++++++++++++++++++- docs/news.xml | 5 +++-- docs/schemas/network.rng | 5 +++++ src/conf/network_conf.c | 31 ++++++++++++++++++++++++++++++- src/conf/network_conf.h | 1 + tests/networkxml2xmlin/set-mtu.xml | 12 ++++++++++++ tests/networkxml2xmlout/set-mtu.xml | 12 ++++++++++++ tests/networkxml2xmltest.c | 1 + 8 files changed, 82 insertions(+), 4 deletions(-) create mode 100644 tests/networkxml2xmlin/set-mtu.xml create mode 100644 tests/networkxml2xmlout/set-mtu.xml diff --git a/docs/formatnetwork.html.in b/docs/formatnetwork.html.in index 8638df9..777c341 100644 --- a/docs/formatnetwork.html.in +++ b/docs/formatnetwork.html.in @@ -93,6 +93,7 @@ <pre> ... &lt;bridge name="virbr0" stp="on" delay="5" macTableManager="libvirt"/&gt; +&lt;mtu size="9000"/&gt; &lt;domain name="example.com" localOnly="no"/&gt; &lt;forward mode="nat" dev="eth0"/&gt; ...</pre> @@ -151,9 +152,25 @@ <span class="since">Since 1.2.11, requires kernel 3.17 or newer</span> </p> + </dd> - + <dt><code>mtu</code></dt> + <dd> + The <code>size</code> attribute of the <code>mtu></code> + element specifies the Maximum Transmission Unit (MTU) for the + network. <span class="since">Since 3.1.0</span>. In the case + of a libvirt-managed network (one with forward mode + of <code>nat</code>, <code>route</code>, <code>open</code>, or + no <code>forward</code> element (i.e. an isolated network), + this will be the MTU assigned to the bridge device when + libvirt creates it, and thereafter also assigned to all tap + devices created to connect guest interfaces. Network types not + specifically mentioned here don't support having an MTU set in + the libvirt network config. If mtu size is unspecified, the + default setting for the type of device being used is assumed + (usually 1500). </dd> + <dt><code>domain</code></dt> <dd> The <code>name</code> attribute on the <code>domain</code> diff --git a/docs/news.xml b/docs/news.xml index f408293..8f0d3d6 100644 --- a/docs/news.xml +++ b/docs/news.xml @@ -36,10 +36,11 @@ </change> <change> <summary> - Introduce MTU to domain &lt;interface/&gt; + Introduce MTU to domain &lt;interface/&gt; and &lt;network&gt; </summary> <description> - Allow setting MTU size for some types of domain interface. + Allow setting MTU size for some types of domain interface + and network. </description> </change> </section> diff --git a/docs/schemas/network.rng b/docs/schemas/network.rng index 8f0a61b..1048dab 100644 --- a/docs/schemas/network.rng +++ b/docs/schemas/network.rng @@ -79,6 +79,11 @@ </element> </optional> + <!-- <mtu> element --> + <optional> + <ref name="mtu"/> + </optional> + <!-- <mac> element --> <optional> <element name="mac"> diff --git a/src/conf/network_conf.c b/src/conf/network_conf.c index 86ce311..0e20dac 100644 --- a/src/conf/network_conf.c +++ b/src/conf/network_conf.c @@ -2242,6 +2242,17 @@ virNetworkDefParseXML(xmlXPathContextPtr ctxt) def->mac_specified = true; } + tmp = virXPathString("string(./mtu/@size)", ctxt); + if (tmp) { + if (virStrToLong_ui(tmp, NULL, 10, &def->mtu) < 0) { + virReportError(VIR_ERR_XML_ERROR, + _("Invalid mtu size '%s' in network '%s'"), + tmp, def->name); + goto error; + } + } + VIR_FREE(tmp); + dnsNode = virXPathNode("./dns", ctxt); if (dnsNode != NULL && virNetworkDNSDefParseXML(def->name, dnsNode, ctxt, &def->dns) < 0) { @@ -2435,7 +2446,9 @@ virNetworkDefParseXML(xmlXPathContextPtr ctxt) case VIR_NETWORK_FORWARD_BRIDGE: if (def->delay || stp) { virReportError(VIR_ERR_XML_ERROR, - _("bridge delay/stp options only allowed in route, nat, and isolated mode, not in %s (network '%s')"), + _("bridge delay/stp options only allowed in " + "route, nat, and isolated mode, not in %s " + "(network '%s')"), virNetworkForwardTypeToString(def->forward.type), def->name); goto error; @@ -2454,6 +2467,19 @@ virNetworkDefParseXML(xmlXPathContextPtr ctxt) VIR_FREE(stp); + if (def->mtu && + (def->forward.type != VIR_NETWORK_FORWARD_NONE && + def->forward.type != VIR_NETWORK_FORWARD_NAT && + def->forward.type != VIR_NETWORK_FORWARD_ROUTE && + def->forward.type != VIR_NETWORK_FORWARD_OPEN)) { + virReportError(VIR_ERR_XML_ERROR, + _("mtu size only allowed in open, route, nat, " + "and isolated mode, not in %s (network '%s')"), + virNetworkForwardTypeToString(def->forward.type), + def->name); + goto error; + } + /* Extract custom metadata */ if ((metadataNode = virXPathNode("./metadata[1]", ctxt)) != NULL) { def->metadata = xmlCopyNode(metadataNode, 1); @@ -2964,6 +2990,9 @@ virNetworkDefFormatBuf(virBufferPtr buf, virBufferAddLit(buf, "/>\n"); } + if (def->mtu) + virBufferAsprintf(buf, "<mtu size='%u'/>\n", def->mtu); + if (def->mac_specified) { char macaddr[VIR_MAC_STRING_BUFLEN]; virMacAddrFormat(&def->mac, macaddr); diff --git a/src/conf/network_conf.h b/src/conf/network_conf.h index b5c9ea2..9e4ae71 100644 --- a/src/conf/network_conf.h +++ b/src/conf/network_conf.h @@ -240,6 +240,7 @@ struct _virNetworkDef { int domainLocalOnly; /* enum virTristateBool: yes disables dns forwarding */ unsigned long delay; /* Bridge forward delay (ms) */ bool stp; /* Spanning tree protocol */ + unsigned int mtu; /* MTU for bridge, 0 means "default" i.e. unset in config */ virMacAddr mac; /* mac address of bridge device */ bool mac_specified; diff --git a/tests/networkxml2xmlin/set-mtu.xml b/tests/networkxml2xmlin/set-mtu.xml new file mode 100644 index 0000000..d1ef32a --- /dev/null +++ b/tests/networkxml2xmlin/set-mtu.xml @@ -0,0 +1,12 @@ +<network ipv6='no'> + <name>private</name> + <uuid>81ff0d90-c91e-6742-64da-4a736edb9a9b</uuid> + <bridge name='virbr2'/> + <mtu size='9000'/> + <mac address='52:54:00:17:3F:37'/> + <ip address="192.168.152.1" netmask="255.255.255.0"> + <dhcp> + <range start="192.168.152.2" end="192.168.152.254"/> + </dhcp> + </ip> +</network> diff --git a/tests/networkxml2xmlout/set-mtu.xml b/tests/networkxml2xmlout/set-mtu.xml new file mode 100644 index 0000000..10e8155 --- /dev/null +++ b/tests/networkxml2xmlout/set-mtu.xml @@ -0,0 +1,12 @@ +<network> + <name>private</name> + <uuid>81ff0d90-c91e-6742-64da-4a736edb9a9b</uuid> + <bridge name='virbr2' stp='on' delay='0'/> + <mtu size='9000'/> + <mac address='52:54:00:17:3f:37'/> + <ip address='192.168.152.1' netmask='255.255.255.0'> + <dhcp> + <range start='192.168.152.2' end='192.168.152.254'/> + </dhcp> + </ip> +</network> diff --git a/tests/networkxml2xmltest.c b/tests/networkxml2xmltest.c index 01cd6f7..cfaf718 100644 --- a/tests/networkxml2xmltest.c +++ b/tests/networkxml2xmltest.c @@ -158,6 +158,7 @@ mymain(void) DO_TEST_PARSE_ERROR("hostdev-duplicate"); DO_TEST_PARSE_ERROR("passthrough-duplicate"); DO_TEST("metadata"); + DO_TEST("set-mtu"); return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE; } -- 2.9.3

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 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?) (I hope we don't have to add a "<mtu auto='yes'/>" and only set host_mtu when that is present :-/) 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). --- New in V2. src/qemu/qemu_command.c | 32 ++++++++++++++++++++++---------- src/qemu/qemu_command.h | 3 ++- src/qemu/qemu_hotplug.c | 5 +++-- src/qemu/qemu_interface.c | 5 +++-- src/qemu/qemu_interface.h | 3 ++- 5 files changed, 32 insertions(+), 16 deletions(-) diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index 6d65872..522152d 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -3555,7 +3555,8 @@ qemuBuildNicDevStr(virDomainDefPtr def, int vlan, unsigned int bootindex, size_t vhostfdSize, - virQEMUCapsPtr qemuCaps) + virQEMUCapsPtr qemuCaps, + unsigned int mtu) { virBuffer buf = VIR_BUFFER_INITIALIZER; const char *nic = net->model; @@ -3679,13 +3680,23 @@ qemuBuildNicDevStr(virDomainDefPtr def, virBufferAsprintf(&buf, ",rx_queue_size=%u", net->driver.virtio.rx_queue_size); } - if (usingVirtio && net->mtu) { - if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_VIRTIO_NET_HOST_MTU)) { - virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s", - _("setting MTU is not supported with this QEMU binary")); - goto error; + if (usingVirtio && mtu) { + if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_VIRTIO_NET_HOST_MTU)) { + + virBufferAsprintf(&buf, ",host_mtu=%u", mtu); + + } else { + /* log an error if mtu was requested specifically for this + * interface, otherwise, if it's just what was reported by + * the attached network, ignore it. + */ + if (net->mtu) { + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s", + _("setting MTU is not supported with " + "this QEMU binary")); + goto error; + } } - virBufferAsprintf(&buf, ",host_mtu=%u", net->mtu); } if (vlan == -1) @@ -8042,7 +8053,7 @@ qemuBuildVhostuserCommandLine(virQEMUDriverPtr driver, VIR_FREE(netdev); if (!(nic = qemuBuildNicDevStr(def, net, -1, bootindex, - queues, qemuCaps))) { + queues, qemuCaps, net->mtu))) { virReportError(VIR_ERR_INTERNAL_ERROR, "%s", _("Error generating NIC -device string")); goto error; @@ -8088,6 +8099,7 @@ qemuBuildInterfaceCommandLine(virQEMUDriverPtr driver, virDomainNetType actualType = virDomainNetGetActualType(net); virNetDevBandwidthPtr actualBandwidth; size_t i; + unsigned int mtu = net->mtu; if (!bootindex) @@ -8142,7 +8154,7 @@ qemuBuildInterfaceCommandLine(virQEMUDriverPtr driver, memset(tapfd, -1, tapfdSize * sizeof(tapfd[0])); if (qemuInterfaceBridgeConnect(def, driver, net, - tapfd, &tapfdSize) < 0) + tapfd, &tapfdSize, &mtu) < 0) goto cleanup; break; @@ -8322,7 +8334,7 @@ qemuBuildInterfaceCommandLine(virQEMUDriverPtr driver, } if (qemuDomainSupportsNicdev(def, net)) { if (!(nic = qemuBuildNicDevStr(def, net, vlan, bootindex, - vhostfdSize, qemuCaps))) + vhostfdSize, qemuCaps, mtu))) goto cleanup; virCommandAddArgList(cmd, "-device", nic, NULL); } else { diff --git a/src/qemu/qemu_command.h b/src/qemu/qemu_command.h index 3bcfdc6..69fe846 100644 --- a/src/qemu/qemu_command.h +++ b/src/qemu/qemu_command.h @@ -101,7 +101,8 @@ char *qemuBuildNicDevStr(virDomainDefPtr def, int vlan, unsigned int bootindex, size_t vhostfdSize, - virQEMUCapsPtr qemuCaps); + virQEMUCapsPtr qemuCaps, + unsigned int mtu); char *qemuDeviceDriveHostAlias(virDomainDiskDefPtr disk); diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c index a6de254..c0d1ab9 100644 --- a/src/qemu/qemu_hotplug.c +++ b/src/qemu/qemu_hotplug.c @@ -969,6 +969,7 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver, bool charDevPlugged = false; bool netdevPlugged = false; bool hostPlugged = false; + unsigned int mtu = net->mtu; /* preallocate new slot for device */ if (VIR_REALLOC_N(vm->def->nets, vm->def->nnets + 1) < 0) @@ -1025,7 +1026,7 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver, goto cleanup; memset(vhostfd, -1, sizeof(*vhostfd) * vhostfdSize); if (qemuInterfaceBridgeConnect(vm->def, driver, net, - tapfd, &tapfdSize) < 0) + tapfd, &tapfdSize, &mtu) < 0) goto cleanup; iface_connected = true; if (qemuInterfaceOpenVhostNet(vm->def, net, priv->qemuCaps, @@ -1236,7 +1237,7 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver, VIR_FORCE_CLOSE(vhostfd[i]); if (!(nicstr = qemuBuildNicDevStr(vm->def, net, vlan, 0, - queueSize, priv->qemuCaps))) + queueSize, priv->qemuCaps, mtu))) goto try_remove; qemuDomainObjEnterMonitor(driver, vm); diff --git a/src/qemu/qemu_interface.c b/src/qemu/qemu_interface.c index ce448d2..c5dca60 100644 --- a/src/qemu/qemu_interface.c +++ b/src/qemu/qemu_interface.c @@ -503,7 +503,8 @@ qemuInterfaceBridgeConnect(virDomainDefPtr def, virQEMUDriverPtr driver, virDomainNetDefPtr net, int *tapfd, - size_t *tapfdSize) + size_t *tapfdSize, + unsigned int *mtu) { const char *brname; int ret = -1; @@ -544,7 +545,7 @@ qemuInterfaceBridgeConnect(virDomainDefPtr def, def->uuid, tunpath, tapfd, *tapfdSize, virDomainNetGetActualVirtPortProfile(net), virDomainNetGetActualVlan(net), - 0, NULL, + net->mtu, mtu, tap_create_flags) < 0) { virDomainAuditNetDevice(def, net, tunpath, false); goto cleanup; diff --git a/src/qemu/qemu_interface.h b/src/qemu/qemu_interface.h index 66ead2a..0ec873f 100644 --- a/src/qemu/qemu_interface.h +++ b/src/qemu/qemu_interface.h @@ -50,7 +50,8 @@ int qemuInterfaceBridgeConnect(virDomainDefPtr def, virQEMUDriverPtr driver, virDomainNetDefPtr net, int *tapfd, - size_t *tapfdSize) + size_t *tapfdSize, + unsigned int *mtu) ATTRIBUTE_NONNULL(2); int qemuInterfaceOpenVhostNet(virDomainDefPtr def, -- 2.9.3