[PATCH] qemuProcessSetupDisksTransientHotplug: skip system_reset when the all disks have transient shareBacking option

[Masayoshi Mizuma <msys.mizuma@xxxxxxxxx>]

From: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>

When both <on_reboot>destroy</on_reboot/> and <transient shareBacking='yes'>
is set to the domain xml, the guest doesn't start.

# virsh start Guest
error: Failed to start domain 'Guest'
error: internal error: qemu unexpectedly closed the monitor
#

That's because libvirt does system_reset qmp command when 
<transient shareBacking='yes'> is set, and the qemu is launched
with '-no-reboot' option, so system_reset goes to shutdown.

The boot order issue happens only if the guest has not only the
transient share backing disks but also disks which isn't set the
option.

Let's skip system_reset when the all disks has the option.

Signed-off-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
---
 src/qemu/qemu_process.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 2b03b0ab98..82dba64e21 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -7058,7 +7058,8 @@ qemuProcessSetupDisksTransientHotplug(virDomainObj *vm,
                                       qemuDomainAsyncJob asyncJob)
 {
     qemuDomainObjPrivate *priv = vm->privateData;
-    bool hasHotpluggedDisk = false;
+    bool needReset = true;
+    size_t attached = 0;
     size_t i;
 
     for (i = 0; i < vm->def->ndisks; i++) {
@@ -7071,12 +7072,24 @@ qemuProcessSetupDisksTransientHotplug(virDomainObj *vm,
         if (qemuDomainAttachDiskGeneric(priv->driver, vm, domdisk, asyncJob) < 0)
             return -1;
 
-        hasHotpluggedDisk = true;
+        attached++;
+    }
+
+    /* system_reset is needed in case the domain also has the other disks (doesn't
+     * have <transient shareBacking='yes'/> option) to fix the boot order. */
+    if (!attached || vm->def->ndisks == attached)
+        needReset = false;
+
+    if (needReset && priv->allowReboot == VIR_TRISTATE_BOOL_NO) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("Doesn't support this configuration. "
+                         "Change the domain xml to allow rebooting the guest."));
+        return -1;
     }
 
     /* in order to allow booting from such disks we need to issue a system-reset
      * so that the firmware tables recording bootable devices are regerated */
-    if (hasHotpluggedDisk) {
+    if (needReset) {
         int rc;
 
         if (qemuDomainObjEnterMonitorAsync(priv->driver, vm, asyncJob) < 0)
-- 
2.27.0