qemu: Be more forgiving when acquiring QUERY job when formatting domain XML

[PATCH] qemu: Be more forgiving when acquiring QUERY job when formatting domain XML

Posted by Michal Privoznik via Devel 2 months, 3 weeks ago

From: Michal Privoznik <mprivozn@redhat.com>

In my previous commit of v11.0.0-rc1~115 I've made QEMU driver
implementation for virDomainGetXMLDesc() (qemuDomainGetXMLDesc())
acquire QERY job. See its commit message for more info. But this
unfortunately broke apps witch fetch domain XML for incoming
migration (like virt-manager). The reason is that for incoming
migration the VIR_ASYNC_JOB_MIGRATION_IN async job is set, but
the mask of allowed synchronous jobs is empty (because QEMU can't
talk on monitor really). This makes virDomainObjBeginJob() fail
which in turn makes qemuDomainGetXMLDesc() fail too.

It makes sense for qemuDomainGetXMLDesc() to acquire the job
(e.g. so that it's coherent with another thread that might be in
the middle of a MODIFY job). But failure to dump XML may be
treated as broken daemon (e.g. virt-manager does so).

Therefore, still try to acquire the QUERY job (if job mask
permits it) but, do not treat failure as an error.

Fixes: 6cc93bf28842526be2fd596a607ebca796b7fb2e
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2369243
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/qemu/qemu_driver.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index b3b0ee66f8..9b583ad7aa 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -6182,6 +6182,7 @@ static char
 {
     virQEMUDriver *driver = dom->conn->privateData;
     virDomainObj *vm;
+    bool hasJob = false;
     char *ret = NULL;
 
     virCheckFlags(VIR_DOMAIN_XML_COMMON_FLAGS | VIR_DOMAIN_XML_UPDATE_CPU,
@@ -6193,8 +6194,10 @@ static char
     if (virDomainGetXMLDescEnsureACL(dom->conn, vm->def, flags) < 0)
         goto cleanup;
 
-    if (virDomainObjBeginJob(vm, VIR_JOB_QUERY) < 0)
-        goto cleanup;
+    if (virDomainNestedJobAllowed(vm->job, VIR_JOB_QUERY) &&
+        virDomainObjBeginJob(vm, VIR_JOB_QUERY) >= 0) {
+        hasJob = true;
+    }
 
     qemuDomainUpdateCurrentMemorySize(vm);
 
@@ -6210,7 +6213,8 @@ static char
 
     ret = qemuDomainFormatXML(driver, vm, flags);
 
-    virDomainObjEndJob(vm);
+    if (hasJob)
+        virDomainObjEndJob(vm);
 
  cleanup:
     virDomainObjEndAPI(&vm);
-- 
2.49.0

Re: [PATCH] qemu: Be more forgiving when acquiring QUERY job when formatting domain XML

Posted by Pavel Hrdina via Devel 2 months, 3 weeks ago

On Mon, Jun 16, 2025 at 10:45:15AM +0200, Michal Privoznik via Devel wrote:
> From: Michal Privoznik <mprivozn@redhat.com>
> 
> In my previous commit of v11.0.0-rc1~115 I've made QEMU driver
> implementation for virDomainGetXMLDesc() (qemuDomainGetXMLDesc())
> acquire QERY job. See its commit message for more info. But this
> unfortunately broke apps witch fetch domain XML for incoming
> migration (like virt-manager). The reason is that for incoming
> migration the VIR_ASYNC_JOB_MIGRATION_IN async job is set, but
> the mask of allowed synchronous jobs is empty (because QEMU can't
> talk on monitor really). This makes virDomainObjBeginJob() fail
> which in turn makes qemuDomainGetXMLDesc() fail too.
> 
> It makes sense for qemuDomainGetXMLDesc() to acquire the job
> (e.g. so that it's coherent with another thread that might be in
> the middle of a MODIFY job). But failure to dump XML may be
> treated as broken daemon (e.g. virt-manager does so).
> 
> Therefore, still try to acquire the QUERY job (if job mask
> permits it) but, do not treat failure as an error.
> 
> Fixes: 6cc93bf28842526be2fd596a607ebca796b7fb2e
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2369243
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> ---
>  src/qemu/qemu_driver.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>