Enhance documentation, improve interoperability, and fix defects in

FreeBSD's front and back Xen blkif interface drivers.

sys/dev/xen/blkfront/block.h:
sys/dev/xen/blkfront/blkfront.c:
sys/dev/xen/blkback/blkback.c:
	Replace FreeBSD specific multi-page ring impelementation with
	support for both the Citrix and Amazon/RedHat versions of this
	extension.

sys/dev/xen/blkfront/blkfront.c:
	o Add a per-instance sysctl tree that exposes all negotiated
	  transport parameters (ring pages, max number of requests,
	  max request size, max number of segments).
	o In blkfront_vdevice_to_unit() add a missing return statement
	  so that we properly identify the unit number for high numbered
	  xvd devices.

sys/dev/xen/blkback/blkback.c:
	o Add static dtrace probes for several events in this driver.
	o Defer connection shutdown processing until the front-end
	  enters the closed state.  This avoids prematurely tearing
	  down the connection when buggy front-ends transition to the
	  closing state, even though the device is open and they
	  veto the close request from the tool stack.
	o Add nodes for maximum request size and the number of active
	  ring pages to the exising, per-instance, sysctl tree.
	o Miscelaneous style cleanup.

sys/xen/interface/io/blkif.h:
	o Add extensive documentation of the XenStore nodes used to
	  implement the blkif interface.
	o Document the startup sequence between a front and back driver.
	o Add structures and documenatation for the "discard" feature
	  (AKA Trim).
	o Cleanup some definitions related to FreeBSD's request
	  number/size/segment-limit extension.

sys/dev/xen/blkfront/blkfront.c:
sys/dev/xen/blkback/blkback.c:
sys/xen/xenbus/xenbusvar.h:
	Add the convenience function xenbus_get_otherend_state() and
	use it to simplify some logic in both block-front and block-back.

MFC after:	1 day

1 files changed, 14 insertions, 0 deletions

diff --git a/sys/xen/xenbus/xenbusvar.h b/sys/xen/xenbus/xenbusvar.h
index bf2a342..1c730fb 100644
--- a/sys/xen/xenbus/xenbusvar.h
+++ b/sys/xen/xenbus/xenbusvar.h
@@ -104,6 +104,20 @@ XENBUS_ACCESSOR(otherend_path,	OTHEREND_PATH,		const char *)
 XenbusState xenbus_read_driver_state(const char *path);
 
 /**
+ * Return the state of the "other end" (peer) of a XenBus device.
+ *
+ * \param dev   The XenBus device whose peer to query.
+ *
+ * \return  The current state of the peer device or XenbusStateClosed if no
+ *          state can be read.
+ */
+static inline XenbusState
+xenbus_get_otherend_state(device_t dev)
+{
+	return (xenbus_read_driver_state(xenbus_get_otherend_path(dev)));
+}
+
+/**
  * Initialize and register a watch on the given path (client suplied storage).
  *
  * \param dev       The XenBus device requesting the watch service.