[PATCH] qemu: forbid updating any attributes of an interface <backend> with update-device

[Martin Kletzander]

On Wed, Feb 15, 2023 at 04:06:41PM -0500, Laine Stump wrote:
>Changing any of the attributes of an <interface>'s <backend> would
>require removing and re-adding the interface for the new setting to
>take effect, so fail any update-device that changes anything in
><backend>
>
>Resolves: https://bugzilla.redhat.com/2169245
>Signed-off-by: Laine Stump <laine at redhat.com>
>---
> src/conf/domain_conf.c   | 14 ++++++++++++++
> src/conf/domain_conf.h   |  2 ++
> src/libvirt_private.syms |  1 +
> src/qemu/qemu_hotplug.c  |  9 +++++++++
> 4 files changed, 26 insertions(+)
>
>diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
>index 3dfc5c87af..aa7bed7dc3 100644
>--- a/src/conf/domain_conf.c
>+++ b/src/conf/domain_conf.c
>@@ -19853,6 +19853,20 @@ virDomainFsDefCheckABIStability(virDomainFSDef *src,
> }
>
>
>+bool
>+virDomainNetBackendIsEqual(virDomainNetBackend *src,
>+                           virDomainNetBackend *dst)
>+{
>+    if (src->type != dst->type ||
>+        STRNEQ_NULLABLE(src->tap, dst->tap) ||
>+        STRNEQ_NULLABLE(src->vhost, dst->vhost) ||
>+        STRNEQ_NULLABLE(src->logFile, dst->logFile)) {

I thought you are missing the @upstream member comparison here, but it
looks like it is not used anywhere in the code.  So I guess

Reviewed-by: Martin Kletzander <mkletzan at redhat.com>

and I'll do some grave-digging about the long lost member.

[...]

>diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
>index c490e2b97a..b4cddef9f5 100644
>--- a/src/qemu/qemu_hotplug.c
>+++ b/src/qemu/qemu_hotplug.c
>@@ -3675,6 +3675,15 @@ qemuDomainChangeNet(virQEMUDriver *driver,
>         goto cleanup;
>     }
>
>+    /* nothing in <backend> can be modified in an existing interface -
>+     * the entire device will need to be removed and re-added.

If I were a nit picker I could tell you to start the sentence with an
uppercase letter or remove the full stop.  O:-)

>+     */
>+    if (!virDomainNetBackendIsEqual(&olddev->backend, &newdev->backend)) {
>+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
>+                       _("cannot modify network device backend settings"));
>+        goto cleanup;
>+    }
>+
>     /* allocate new actual device to compare to old - we will need to
>      * free it if we fail for any reason
>      */
>-- 
>2.39.1
>
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