Originally qemuDomainAttachNetDevice() would wait until the cleanup at
the very end of the function to add newly hotplugged interfaces to the
domain's nets list. commit 7b8bec4560 modified it to add the new
interface to the nets list earlier (but not all the way at the
beginning of the function either, because there are some operations
(PCI address assignment in particular) that need the new device to not
yet be visible in the domaindef).

But hostdev interfaces short-circuit past most of the body of
qemuDomainAttachNetDevice() (since none of it applies to hostdev
interfaces). In the past that was okay, but since the line that adds
the new interface to the domaindef's nets list is in that "most of the
body", after that commit hotplugged hostdev interfaces are no longer
being properly added to the domaindef nets list, so they don't show up
in the status XML or the virsh domiflist output.

It really *is* important to add interfaces to the nets list earlier,
so we can't revert commit 7b8bec4560, and we also can't move the
insert to common code *earlier* in the function, so instead this patch
duplicates the VIR_APPEND_ELEMENT_COPY() just before the code path for
hostdev interfaces jumps to cleanup.

Resolves: https://bugzilla.redhat.com/1972991
Fixes: 7b8bec45601b6570f6a7413e94d291986d2663f1
(any other tags I should add?)

Signed-off-by: Laine Stump <laine@redhat.com>
---
 src/qemu/qemu_hotplug.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
index 0640cdd9f7..e323edc2e8 100644
--- a/src/qemu/qemu_hotplug.c
+++ b/src/qemu/qemu_hotplug.c
@@ -1230,10 +1230,21 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver,
         /* This is really a "smart hostdev", so it should be attached
          * as a hostdev (the hostdev code will reach over into the
          * netdev-specific code as appropriate), then also added to
-         * the nets list (see cleanup:) if successful.
+         * the nets list if successful.
          */
-        ret = qemuDomainAttachHostDevice(driver, vm,
-                                         virDomainNetGetActualHostdev(net));
+        if (qemuDomainAttachHostDevice(driver, vm,
+                                       virDomainNetGetActualHostdev(net)) < 0) {
+            goto cleanup;
+        }
+        if (VIR_APPEND_ELEMENT_COPY(vm->def->nets, vm->def->nnets, net) < 0)
+            goto cleanup;
+
+        /* the rest of the setup doesn't apply to hostdev interfaces, so
+         * we can skip straight to the cleanup (nothing there applies to
+         * hostdev interfaces either, but it might in the future, so we
+         * may as well be consistent)
+         */
+        ret = 0;
         goto cleanup;
     }
 
-- 
2.31.1

On 6/17/21 7:36 AM, Laine Stump wrote:
> Originally qemuDomainAttachNetDevice() would wait until the cleanup at
> the very end of the function to add newly hotplugged interfaces to the
> domain's nets list. commit 7b8bec4560 modified it to add the new
> interface to the nets list earlier (but not all the way at the
> beginning of the function either, because there are some operations
> (PCI address assignment in particular) that need the new device to not
> yet be visible in the domaindef).
> 
> But hostdev interfaces short-circuit past most of the body of
> qemuDomainAttachNetDevice() (since none of it applies to hostdev
> interfaces). In the past that was okay, but since the line that adds
> the new interface to the domaindef's nets list is in that "most of the
> body", after that commit hotplugged hostdev interfaces are no longer
> being properly added to the domaindef nets list, so they don't show up
> in the status XML or the virsh domiflist output.
> 
> It really *is* important to add interfaces to the nets list earlier,
> so we can't revert commit 7b8bec4560, and we also can't move the
> insert to common code *earlier* in the function, so instead this patch
> duplicates the VIR_APPEND_ELEMENT_COPY() just before the code path for
> hostdev interfaces jumps to cleanup.
> 
> Resolves: https://bugzilla.redhat.com/1972991
> Fixes: 7b8bec45601b6570f6a7413e94d291986d2663f1
> (any other tags I should add?)
> 

No.

> Signed-off-by: Laine Stump <laine@redhat.com>
> ---
>  src/qemu/qemu_hotplug.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)


Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

Michal