[libvirt] [PATCHv2] qemu: don't leak vm on failure

[Eric Blake]

Failure to attach to a domain during 'virsh qemu-attach' left
the list of domains in an odd state:

$ virsh qemu-attach 4176
error: An error occurred, but the cause is unknown

$ virsh list --all
 Id    Name                           State
----------------------------------------------------
 2     foo                            shut off

$ virsh qemu-attach 4176
error: Requested operation is not valid: domain is already active as 'foo'

$ virsh undefine foo
error: Failed to undefine domain foo
error: Requested operation is not valid: cannot undefine transient domain

$ virsh shutdown foo
error: Failed to shutdown domain foo
error: invalid argument: monitor must not be NULL

It all stems from leaving the list of domains unmodified on
the initial failure; we should follow the lead of createXML
which removes vm on failure (the actual initial failure still
needs to be fixed in a later patch, but at least this patch
gets us to the point where we aren't getting stuck with an
unremovable "shut off" transient domain).

While investigating, I also found a leak in qemuDomainCreateXML;
the two functions should behave similarly.  Note that there are
still two unusual paths: if dom is not allocated, the user will
see an OOM error even though the vm remains registered (but oom
errors already indicate tricky cleanup); and if the vm starts
and then quits again all before the job ends, it is possible
to return a non-NULL dom even though the dom will no longer be
useful for anything (but this at least lets the user know their
short-lived vm ran).

* src/qemu/qemu_driver.c (qemuDomainCreateXML): Don't leak vm on
failure to obtain job.
(qemuDomainQemuAttach): Match cleanup of qemuDomainCreateXML.

Signed-off-by: Eric Blake <eblake at redhat.com>
---

v1 was discussed here: https://www.redhat.com/archives/libvir-list/2013-September/msg00362.html
changes since then: plug another leak of vm, and clean up some style.
Expand the commit message to explain unusual paths.

 src/qemu/qemu_driver.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index e37fe33..6dafa2b 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -1602,8 +1602,11 @@ static virDomainPtr qemuDomainCreateXML(virConnectPtr conn,

     def = NULL;

-    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0)
-        goto cleanup; /* XXXX free the 'vm' we created ? */
+    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0) {
+        qemuDomainRemoveInactive(driver, vm);
+        vm = NULL;
+        goto cleanup;
+    }

     if (qemuProcessStart(conn, driver, vm, NULL, -1, NULL, NULL,
                          VIR_NETDEV_VPORT_PROFILE_OP_CREATE,
@@ -1631,10 +1634,10 @@ static virDomainPtr qemuDomainCreateXML(virConnectPtr conn,
     virDomainAuditStart(vm, "booted", true);

     dom = virGetDomain(conn, vm->def->name, vm->def->uuid);
-    if (dom) dom->id = vm->def->id;
+    if (dom)
+        dom->id = vm->def->id;

-    if (vm &&
-        qemuDomainObjEndJob(driver, vm) == 0)
+    if (qemuDomainObjEndJob(driver, vm) == 0)
         vm = NULL;

 cleanup:
@@ -13630,34 +13633,38 @@ static virDomainPtr qemuDomainQemuAttach(virConnectPtr conn,

     def = NULL;

-    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0)
+    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0) {
+        qemuDomainRemoveInactive(driver, vm);
+        vm = NULL;
         goto cleanup;
+    }

     if (qemuProcessAttach(conn, driver, vm, pid,
                           pidfile, monConfig, monJSON) < 0) {
+        if (qemuDomainObjEndJob(driver, vm) > 0)
+            qemuDomainRemoveInactive(driver, vm);
+        vm = NULL;
         monConfig = NULL;
-        goto endjob;
+        goto cleanup;
     }

     monConfig = NULL;

     dom = virGetDomain(conn, vm->def->name, vm->def->uuid);
-    if (dom) dom->id = vm->def->id;
+    if (dom)
+        dom->id = vm->def->id;

-endjob:
     if (qemuDomainObjEndJob(driver, vm) == 0) {
         vm = NULL;
-        goto cleanup;
-    }

 cleanup:
     virDomainDefFree(def);
-    virObjectUnref(qemuCaps);
     virDomainChrSourceDefFree(monConfig);
     if (vm)
         virObjectUnlock(vm);
     VIR_FREE(pidfile);
     virObjectUnref(caps);
+    virObjectUnref(qemuCaps);
     return dom;
 }

-- 
1.8.3.1