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qemu: re-use existing ActualNetDef for more interface types during update-device

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For the full history behind this patch, look at the following:

   https://issues.redhat.com/browse/RHEL-7036
   commit v10.7.0-101-ga37bd2a15b
   commit v10.8.0-rc2-8-gbcd5ae4e73

Summary: original problem was unexpected failure of update-device when
the user hadn't changed anything other than online status of the guest
NIC (which should always be allowed).

The first commit "fixed" this by avoiding the allocation of a new
ActualNetDef (i.e. creating a new networkport) for *all* network
device updates (because that was inappropriately changing which
ethernet physdev should be used for a macvtap connection, which by
design can't be handled in an update-device).

But this commit caused a regression for update-device of bridge-based
network devices (because some the updates of certain attributes *do*
require the ActualNetDef be re-allocated), so...

The 2nd commit narrowed the list of network types that get the "don't
allocate new ActualNetDef" treatment (so that only interfaces
connected to a network that uses a pool of ethernet VFs *being used in
passthrough mode* qualify).

But then it was pointed out that this re-broke simple updates of
devices that used a direct/macvtap network in "bridge" mode (because
it's possible to list multiple physdevs to use for bridge mode, in
which case the network driver attempts to "load balance" (and so a new
allocation might have a different ethernet physdev which, again, can't
be supported in a device-update).

So this (single line of code) patch *widens* the list of network types
that don't allocate a new ActualNetDef to also include the other
direct (macvtap) modes, e.g. bridge, private, etc.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
This commit is contained in:
Laine Stump 2024-11-25 22:51:04 -05:00
parent 2195037265
commit 4e987a86b5
1 changed files with 20 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
src/qemu/qemu_hotplug.c
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@ -3935,25 +3935,29 @@ qemuDomainChangeNet(virQEMUDriver *driver,
if (newdev->type == VIR_DOMAIN_NET_TYPE_NETWORK) {
if (olddev->type == VIR_DOMAIN_NET_TYPE_NETWORK &&
oldType == VIR_DOMAIN_NET_TYPE_DIRECT &&
virDomainNetGetActualDirectMode(olddev) == VIR_NETDEV_MACVLAN_MODE_PASSTHRU &&
STREQ(olddev->data.network.name, newdev->data.network.name)) {
/* old and new are type='network', and the network name
* hasn't changed *and* this is a network where each
* connection is allocated exclusive use of a VF
* device. In this case we *don't* want to get a new port
* ("actual device") from the network because attempting
* to allocate a new device would also allocate a
* new/different VF, causing the update to fail. And
* anyway we can use olddev's actualNetDef (since it
* hasn't changed).
* hasn't changed *and* this is a "direct" network (a pool
* of 1 or more host ethernet devices where each guest
* interface is allocated one of those physical devices
* that it then connects to via macvtap). In this case we
* *don't* want to get a new port ("actual device") from
* the network because attempting to allocate a new port
* would also allocate a new/different ethernet (physical
* device), causing the update to fail (because the
* physical device of a macvtap-based interface can't be
* changed without completely unplugging and re-plugging
* the guest NIC).
*
* So instead we just duplicate *the pointer to* the
* actualNetDef from olddev to newdev so that comparisons
* of actualNetDef will show no change. If the update is
* successful, we will clear the actualNetDef pointer from
* olddev before destroying it (or if the update fails,
* then we need to clear the pointer from newdev before
* destroying it)
* We can work around this issue by just re-using olddev's
* actualNetDef (since it hasn't changed) rather than
* allocating a new one. We just duplicate *the pointer
* to* the actualNetDef from olddev to newdev so that
* comparisons of actualNetDef will show no change. If the
* update is successful, we will clear the actualNetDef
* pointer from olddev before destroying it (or if the
* update fails, then we need to clear the pointer from
* newdev before destroying it)
*/
newdev->data.network.actual = olddev->data.network.actual;
memcpy(newdev->data.network.portid, olddev->data.network.portid,