hw/ppc/spapr.c: adding pending_dimm_unplugs to sPAPRMachineState

The LMB DRC release callback, spapr_lmb_release(), uses an opaque
parameter, a sPAPRDIMMState struct that stores the current LMBs that
are allocated to a DIMM (nr_lmbs). After each call to this callback,
the nr_lmbs is decremented by one and, when it reaches zero, the callback
proceeds with the qdev calls to hot unplug the LMB.

Using drc->detach_cb_opaque is problematic because it can't be migrated in
the future DRC migration work. This patch makes the following changes to
eliminate the usage of this opaque callback inside spapr_lmb_release:

- sPAPRDIMMState was moved from spapr.c and added to spapr.h. A new
attribute called 'addr' was added to it. This is used as an unique
identifier to associate a sPAPRDIMMState to a PCDIMM element.

- sPAPRMachineState now hosts a new QTAILQ called 'pending_dimm_unplugs'.
This queue of sPAPRDIMMState elements will store the DIMM state of DIMMs
that are currently going under an unplug process.

- spapr_lmb_release() will now retrieve the nr_lmbs value by getting the
correspondent sPAPRDIMMState. A helper function called spapr_dimm_get_address
was created to fetch the address of a PCDIMM device inside spapr_lmb_release.
When nr_lmbs reaches zero and the callback proceeds with the qdev hot unplug
calls, the sPAPRDIMMState struct is removed from spapr->pending_dimm_unplugs.

After these changes, the opaque argument for spapr_lmb_release is now
unused and is passed as NULL inside spapr_del_lmbs. This and the other
opaque arguments can now be safely removed from the code.

As an additional cleanup made by this patch, the spapr_del_lmbs function
was merged with spapr_memory_unplug_request. The former was being called
only by the latter and both were small enough to fit one single function.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
[dwg: Minor stylistic cleanups]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

include/hw/ppc/spapr.h

@@ -32,6 +32,7 @@ struct sPAPRRTCState {
     int64_t ns_offset;
 };
 
+typedef struct sPAPRDIMMState sPAPRDIMMState;
 typedef struct sPAPRMachineClass sPAPRMachineClass;
 
 #define TYPE_SPAPR_MACHINE      "spapr-machine"
@@ -104,6 +105,11 @@ struct sPAPRMachineState {
     /* RTAS state */
     QTAILQ_HEAD(, sPAPRConfigureConnectorState) ccs_list;
 
+    /* Pending DIMM unplug cache. It is populated when a LMB
+     * unplug starts. It can be regenerated if a migration
+     * occurs during the unplug process. */
+    QTAILQ_HEAD(, sPAPRDIMMState) pending_dimm_unplugs;
+
     /*< public >*/
     char *kvm_type;
     MemoryHotplugState hotplug_memory;