Monitor and emit events for XenStore changes to XenBus trees

of the devices we manage.  These changes can be due to writes
we make ourselves or due to changes made by the control domain.
The goal of these changes is to insure that all state transitions
can be detected regardless of their source and to allow common
device policies (e.g. "onlined" backend devices) to be centralized
in the XenBus bus code.

sys/xen/xenbus/xenbusvar.h:
sys/xen/xenbus/xenbus.c:
sys/xen/xenbus/xenbus_if.m:
	Add a new method for XenBus drivers "localend_changed".
	This method is invoked whenever a write is detected to
	a device's XenBus tree.  The default implementation of
	this method is a no-op.

sys/xen/xenbus/xenbus_if.m:
sys/dev/xen/netfront/netfront.c:
sys/dev/xen/blkfront/blkfront.c:
sys/dev/xen/blkback/blkback.c:
	Change the signature of the "otherend_changed" method.
	This notification cannot fail, so it should return void.

sys/xen/xenbus/xenbusb_back.c:
	Add "online" device handling to the XenBus Back Bus
	support code.  An online backend device remains active
	after a front-end detaches as a reconnect is expected
	to occur in the near future.

sys/xen/interface/io/xenbus.h:
	Add comment block further explaining the meaning and
	driver responsibilities associated with the XenBus
	Closed state.

sys/xen/xenbus/xenbusb.c:
sys/xen/xenbus/xenbusb.h:
sys/xen/xenbus/xenbusb_back.c:
sys/xen/xenbus/xenbusb_front.c:
sys/xen/xenbus/xenbusb_if.m:
	o Register a XenStore watch against the local XenBus tree
	  for all devices.
	o Cache the string length of the path to our local tree.
	o Allow the xenbus front and back drivers to hook/filter both
	  local and otherend watch processing.
	o Update the device ivar version of "state" when we detect
	  a XenStore update of that node.

sys/dev/xen/control/control.c:
sys/xen/xenbus/xenbus.c:
sys/xen/xenbus/xenbusb.c:
sys/xen/xenbus/xenbusb.h:
sys/xen/xenbus/xenbusvar.h:
sys/xen/xenstore/xenstorevar.h:
	Allow clients of the XenStore watch mechanism to attach
	a single uintptr_t worth of client data to the watch.
	This removes the need to carefully place client watch
	data within enclosing objects so that a cast or offsetof
	calculation can be used to convert from watch to enclosing
	object.

Sponsored by:	Spectra Logic Corporation
MFC after:	1 week

1 files changed, 20 insertions, 4 deletions

diff --git a/sys/xen/xenbus/xenbusvar.h b/sys/xen/xenbus/xenbusvar.h
index 55d7f29..bf2a342 100644
--- a/sys/xen/xenbus/xenbusvar.h
+++ b/sys/xen/xenbus/xenbusvar.h
@@ -51,8 +51,6 @@
 
 #include <xen/xenstore/xenstorevar.h>
 
-#include "xenbus_if.h"
-
 /* XenBus allocations including XenStore data returned to clients. */
 MALLOC_DECLARE(M_XENBUS);
 
@@ -116,6 +114,8 @@ XenbusState xenbus_read_driver_state(const char *path);
  *                  must be stable for the lifetime of the watch.
  * \param callback  The function to call when XenStore objects at or below
  *                  path are modified.
+ * \param cb_data   Client data that can be retrieved from the watch object
+ *                  during the callback.
  *
  * \return  On success, 0. Otherwise an errno value indicating the
  *          type of failure.
@@ -126,7 +126,8 @@ XenbusState xenbus_read_driver_state(const char *path);
  */
 int xenbus_watch_path(device_t dev, char *path,
 		      struct xs_watch *watch, 
-		      xs_watch_cb_t *callback);
+		      xs_watch_cb_t *callback,
+		      uintptr_t cb_data);
 
 /**
  * Initialize and register a watch at path/path2 in the XenStore.
@@ -138,6 +139,8 @@ int xenbus_watch_path(device_t dev, char *path,
  *                  must be stable for the lifetime of the watch.
  * \param callback  The function to call when XenStore objects at or below
  *                  path are modified.
+ * \param cb_data   Client data that can be retrieved from the watch object
+ *                  during the callback.
  *
  * \return  On success, 0. Otherwise an errno value indicating the
  *          type of failure.
@@ -153,7 +156,8 @@ int xenbus_watch_path(device_t dev, char *path,
  */
 int xenbus_watch_path2(device_t dev, const char *path,
 		       const char *path2, struct xs_watch *watch, 
-		       xs_watch_cb_t *callback);
+		       xs_watch_cb_t *callback,
+		       uintptr_t cb_data);
 
 /**
  * Grant access to the given ring_mfn to the peer of the given device.
@@ -275,4 +279,16 @@ const char *xenbus_strstate(enum xenbus_state state);
  */
 int xenbus_dev_is_online(device_t dev);
 
+/**
+ * Default callback invoked when a change to the local XenStore sub-tree
+ * for a device is modified.
+ * 
+ * \param dev   The XenBus device whose tree was modified.
+ * \param path  The tree relative sub-path to the modified node.  The empty
+ *              string indicates the root of the tree was destroyed.
+ */
+void xenbus_localend_changed(device_t dev, const char *path);
+
+#include "xenbus_if.h"
+
 #endif /* _XEN_XENBUS_XENBUSVAR_H */