OvmfPkg/XenBusDxe: Introduce XenBus support itself.

This is a bus-like on top of XenStore. It will look for advertised
ParaVirtualized devices and initialize them by producing XenBus
protocol.

Change in V4:
- Replace the license by the commonly used file header text.
- Clean XenBus.h header (remove copyright that does not belong to the
  file anymore; and rewrite the brief description of the file)
- Fix description on the function

Change in V3:
- Insert to ChildList later, once populated.
- Remove XENBUS_XENSTORE_NODE macro.
- add comment to XenBusAddDevice and XenBusEnumerateBus about
  concurrency calls.
- Add a description to the introduced member to the protocol.

Change in V2:
- comment, file header
- Fix comment style
- Error handling in the main init function
- coding style
- Fix error path in add device.

Origin: FreeBSD 10.0
License: This patch adds XenBus.c which is under the MIT licence.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16270 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/XenBusDxe/XenBusDxe.h

@@ -82,6 +82,7 @@ extern EFI_COMPONENT_NAME_PROTOCOL  gXenBusDxeComponentName;
 #define PCI_DEVICE_ID_XEN_PLATFORM       0x0001
 
 
+typedef struct _XENBUS_DEVICE_PATH XENBUS_DEVICE_PATH;
 typedef struct _XENBUS_DEVICE XENBUS_DEVICE;
 
 // Have the state of the driver.
@@ -92,11 +93,29 @@ struct _XENBUS_DEVICE {
   EFI_HANDLE                    ControllerHandle;
   EFI_PCI_IO_PROTOCOL           *PciIo;
   EFI_EVENT                     ExitBootEvent;
+  EFI_DEVICE_PATH_PROTOCOL      *DevicePath;
+  LIST_ENTRY                    ChildList;
 
   VOID                          *Hyperpage;
   shared_info_t                 *SharedInfo;
 };
 
+// There is one of this struct allocated for every child.
+#define XENBUS_PRIVATE_DATA_SIGNATURE SIGNATURE_32 ('X', 'B', 'p', 'd')
+typedef struct {
+    UINTN Signature;
+    LIST_ENTRY Link;
+    EFI_HANDLE Handle;
+    XENBUS_PROTOCOL XenBusIo;
+    XENBUS_DEVICE *Dev;
+    XENBUS_DEVICE_PATH *DevicePath;
+} XENBUS_PRIVATE_DATA;
+
+#define XENBUS_PRIVATE_DATA_FROM_THIS(a) \
+  CR (a, XENBUS_PRIVATE_DATA, XenBusIo, XENBUS_PRIVATE_DATA_SIGNATURE)
+#define XENBUS_PRIVATE_DATA_FROM_LINK(a) \
+  CR (a, XENBUS_PRIVATE_DATA, Link, XENBUS_PRIVATE_DATA_SIGNATURE)
+
 /*
  * Helpers
  */