From b36260c361f9d8a854c4d5e9c7309aed7cb99834 Mon Sep 17 00:00:00 2001

Message-Id: <b36260c361f9d8a854c4d5e9c7309aed7cb99834@dist-git>

From: Laine Stump <laine@laine.org>

Date: Tue, 23 May 2017 13:02:42 -0400

Subject: [PATCH] Revert "qemu: propagate bridge MTU into qemu "host_mtu"

 option"

This reverts commit 2841e675.

It turns out that adding the host_mtu field to the PCI capabilities in

the guest bumps the length of PCI capabilities beyond the 32 byte

boundary, so the virtio-net device gets 64 bytes of ioport space

instead of 32, which offsets the address of all the other following

devices. Migration doesn't work very well when the location and length

of PCI capabilities of devices is changed between source and

destination.

This means that we need to make sure that the absence/presence of

host_mtu on the qemu commandline always matches between source and

destination, which means that we need to make setting of host_mtu an

opt-in thing (it can't happen automatically when the bridge being used

has a non-default MTU, which is what commit 2841e675 implemented).

I do want to re-implement this feature with an <mtu auto='on'/>

setting, but probably won't backport that to any stable branches, so

I'm first reverting the original commit, and that revert can be pushed

to the few releases that have been made since the original (3.1.0 -

3.3.0)

Resolves: https://bugzilla.redhat.com/1449346

(cherry picked from commit 77780a29edace958a1f931d3281b962be4f5290e)

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

---

 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, 16 insertions(+), 32 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c

index 30feef1de..4d3a3d8ca 100644

--- a/src/qemu/qemu_command.c

+++ b/src/qemu/qemu_command.c

@@ -3633,8 +3633,7 @@ qemuBuildNicDevStr(virDomainDefPtr def,

                    int vlan,

                    unsigned int bootindex,

                    size_t vhostfdSize,

-                   virQEMUCapsPtr qemuCaps,

-                   unsigned int mtu)

+                   virQEMUCapsPtr qemuCaps)

 {

     virBuffer buf = VIR_BUFFER_INITIALIZER;

     const char *nic = net->model;

@@ -3758,23 +3757,13 @@ qemuBuildNicDevStr(virDomainDefPtr def,

         virBufferAsprintf(&buf, ",rx_queue_size=%u", net->driver.virtio.rx_queue_size);

     }

-    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;

-            }

+    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;

         }

+        virBufferAsprintf(&buf, ",host_mtu=%u", net->mtu);

     }

     if (vlan == -1)

@@ -8275,7 +8264,7 @@ qemuBuildVhostuserCommandLine(virQEMUDriverPtr driver,

     VIR_FREE(netdev);

     if (!(nic = qemuBuildNicDevStr(def, net, -1, bootindex,

-                                   queues, qemuCaps, net->mtu))) {

+                                   queues, qemuCaps))) {

         virReportError(VIR_ERR_INTERNAL_ERROR,

                        "%s", _("Error generating NIC -device string"));

         goto error;

@@ -8321,7 +8310,6 @@ qemuBuildInterfaceCommandLine(virQEMUDriverPtr driver,

     virDomainNetType actualType = virDomainNetGetActualType(net);

     virNetDevBandwidthPtr actualBandwidth;

     size_t i;

-    unsigned int mtu = net->mtu;

     if (!bootindex)

@@ -8376,7 +8364,7 @@ qemuBuildInterfaceCommandLine(virQEMUDriverPtr driver,

         memset(tapfd, -1, tapfdSize * sizeof(tapfd[0]));

         if (qemuInterfaceBridgeConnect(def, driver, net,

-                                       tapfd, &tapfdSize, &mtu) < 0)

+                                       tapfd, &tapfdSize) < 0)

             goto cleanup;

         break;

@@ -8556,7 +8544,7 @@ qemuBuildInterfaceCommandLine(virQEMUDriverPtr driver,

     }

     if (qemuDomainSupportsNicdev(def, net)) {

         if (!(nic = qemuBuildNicDevStr(def, net, vlan, bootindex,

-                                       vhostfdSize, qemuCaps, mtu)))

+                                       vhostfdSize, qemuCaps)))

             goto cleanup;

         virCommandAddArgList(cmd, "-device", nic, NULL);

     } else {

diff --git a/src/qemu/qemu_command.h b/src/qemu/qemu_command.h

index 7da92c8c9..09cb00ee9 100644

--- a/src/qemu/qemu_command.h

+++ b/src/qemu/qemu_command.h

@@ -101,8 +101,7 @@ char *qemuBuildNicDevStr(virDomainDefPtr def,

                          int vlan,

                          unsigned int bootindex,

                          size_t vhostfdSize,

-                         virQEMUCapsPtr qemuCaps,

-                         unsigned int mtu);

+                         virQEMUCapsPtr qemuCaps);

 char *qemuDeviceDriveHostAlias(virDomainDiskDefPtr disk);

diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c

index 5c3660922..cdeb0617a 100644

--- a/src/qemu/qemu_hotplug.c

+++ b/src/qemu/qemu_hotplug.c

@@ -968,7 +968,6 @@ 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 +1024,7 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,

             goto cleanup;

         memset(vhostfd, -1, sizeof(*vhostfd) * vhostfdSize);

         if (qemuInterfaceBridgeConnect(vm->def, driver, net,

-                                       tapfd, &tapfdSize, &mtu) < 0)

+                                       tapfd, &tapfdSize) < 0)

             goto cleanup;

         iface_connected = true;

         if (qemuInterfaceOpenVhostNet(vm->def, net, priv->qemuCaps,

@@ -1239,7 +1238,7 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,

         VIR_FORCE_CLOSE(vhostfd[i]);

     if (!(nicstr = qemuBuildNicDevStr(vm->def, net, vlan, 0,

-                                      queueSize, priv->qemuCaps, mtu)))

+                                      queueSize, priv->qemuCaps)))

         goto try_remove;

     qemuDomainObjEnterMonitor(driver, vm);

diff --git a/src/qemu/qemu_interface.c b/src/qemu/qemu_interface.c

index c643b76ec..e11d69c3e 100644

--- a/src/qemu/qemu_interface.c

+++ b/src/qemu/qemu_interface.c

@@ -503,8 +503,7 @@ qemuInterfaceBridgeConnect(virDomainDefPtr def,

                            virQEMUDriverPtr driver,

                            virDomainNetDefPtr net,

                            int *tapfd,

-                           size_t *tapfdSize,

-                           unsigned int *mtu)

+                           size_t *tapfdSize)

 {

     const char *brname;

     int ret = -1;

@@ -545,7 +544,7 @@ qemuInterfaceBridgeConnect(virDomainDefPtr def,

                                            def->uuid, tunpath, tapfd, *tapfdSize,

                                            virDomainNetGetActualVirtPortProfile(net),

                                            virDomainNetGetActualVlan(net),

-                                           net->coalesce, net->mtu, mtu,

+                                           net->coalesce, 0, NULL,

                                            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 ba74ac2cf..a7faa0b3d 100644

--- a/src/qemu/qemu_interface.h

+++ b/src/qemu/qemu_interface.h

@@ -51,8 +51,7 @@ int qemuInterfaceBridgeConnect(virDomainDefPtr def,

                                virQEMUDriverPtr driver,

                                virDomainNetDefPtr net,

                                int *tapfd,

-                               size_t *tapfdSize,

-                               unsigned int *mtu)

+                               size_t *tapfdSize)

     ATTRIBUTE_NONNULL(2);

 int qemuInterfaceOpenVhostNet(virDomainDefPtr def,

-- 

2.13.0