[Qemu-devel] [PATCH] monitor: fix object_del for command-line-created objects

[Michael Roth]

Currently objects specified on the command-line are only partially
cleaned up when 'object_del' is issued in either HMP or QMP: the
object itself is fully finalized, but the QemuOpts are not removed.
This results in the following behavior:

  x86_64-softmmu/qemu-system-x86_64 -monitor stdio \
    -object memory-backend-ram,id=ram1,size=256M

  QEMU 2.7.91 monitor - type 'help' for more information
  (qemu) object_del ram1
  (qemu) object_del ram1
  object 'ram1' not found
  (qemu) object_add memory-backend-ram,id=ram1,size=256M
  Duplicate ID 'ram1' for object
  Try "help object_add" for more information

which can be an issue for use-cases like memory hotplug.

This happens on the HMP side because hmp_object_add() attempts to
create a temporary QemuOpts entry with ID 'ram1', which ends up
conflicting with the command-line-created entry, since it was never
cleaned up during the previous hmp_object_del() call.

We address this by adding checks in {qmp,hmp}_object_del to determine
whether an option group entry matching the object's ID is present,
and removing it if it is.

Note that qmp_object_add() never attempts to create a temporary
QemuOpts entry, so it does not encounter the duplicate ID error,
which is why this isn't generally visible in libvirt.

Cc: "Dr. David Alan Gilbert" <address@hidden>
Cc: Markus Armbruster <address@hidden>
Cc: Eric Blake <address@hidden>
Cc: Daniel Berrange <address@hidden>
Signed-off-by: Michael Roth <address@hidden>
---
 hmp.c | 10 ++++++++++
 qmp.c | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/hmp.c b/hmp.c
index b869617..99b8bf3 100644
--- a/hmp.c
+++ b/hmp.c
@@ -2072,6 +2072,16 @@ void hmp_object_del(Monitor *mon, const QDict *qdict)
 
     user_creatable_del(id, &err);
     hmp_handle_error(mon, &err);
+
+    /* if object was defined on the command-line, remove its corresponding
+     * option group entry
+     */
+    if (err == NULL) {
+        QemuOptsList *opt_group = qemu_find_opts_err("object", &err);
+        if (opt_group) {
+            qemu_opts_del(qemu_opts_find(opt_group, id));
+        }
+    }
 }
 
 void hmp_info_memdev(Monitor *mon, const QDict *qdict)
diff --git a/qmp.c b/qmp.c
index 0028f0b..87c545d 100644
--- a/qmp.c
+++ b/qmp.c
@@ -686,6 +686,16 @@ void qmp_object_add(const char *type, const char *id,
 void qmp_object_del(const char *id, Error **errp)
 {
     user_creatable_del(id, errp);
+
+    /* if object was defined on the command-line, remove its corresponding
+     * option group entry
+     */
+    if (!(errp && *errp)) {
+        QemuOptsList *opt_group = qemu_find_opts_err("object", errp);
+        if (opt_group) {
+            qemu_opts_del(qemu_opts_find(opt_group, id));
+        }
+    }
 }
 
 MemoryDeviceInfoList *qmp_query_memory_devices(Error **errp)
-- 
1.9.1