tools: Refactor /dev/xen/evtchn wrappers into libxenevtchn.

libxenevtchn will provide a stable API and ABI for accessing the
evtchn device.

The functions are moved into the xenevtchn namespace to make a clean
break from libxc and avoid ambiguity regarding which interfaces are
stable.

All in-tree users are updated to use the new names.

Upon request (via #define XC_WANT_COMPAT_EVTCHN_API) libxenctrl will
provide a compat API for the old names. This is used by qemu-xen for
the time being. qemu-xen-traditional is updated in lockstep.

This leaves a few event channel related functions which go via privcmd
(EVTCHNOP) rather than ioctls on the /dev/xen/evtchn device in
libxenctrl. Specifically:

 - xc_evtchn_alloc_unbound
 - xc_evtchn_reset
 - xc_evtchn_status

Note that xc_evtchn_alloc_unbound's functionality is also provided by
xenevtchn_bind_unbound_port() (née xc_evtchn_bind_unbound_port) and is
probably redundant.

These functions do not appear to be needed by qemu-dm, qemu-pv
(provision of device model to HVM guests and PV backends respectively)
or by libvchan suggesting they are not needed by non-toolstack uses of
event channels. QEMU does use these in hw/xenpv/xen_domainbuild.c but
that is a "toolstack use".

The new library uses a version script to ensure that only expected
symbols are exported and to version them such that ABI guarantees can
be kept in the future.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
[ ijc -- updated MINIOS_UPSTREAM_REVISION and QEMU_TRADITIONAL_REVISION ]

stubdom/Makefile

@@ -319,6 +319,12 @@ mk-headers-$(XEN_TARGET_ARCH): $(IOEMU_LINKFARM_TARGET)
 	  ln -sf $(XEN_ROOT)/tools/libs/toollog/include/*.h . && \
 	  ln -sf $(XEN_ROOT)/tools/libs/toollog/*.c . && \
 	  ln -sf $(XEN_ROOT)/tools/libs/toollog/Makefile . )
+	mkdir -p libs-$(XEN_TARGET_ARCH)/evtchn/include
+	[ -h libs-$(XEN_TARGET_ARCH)/evtchn/Makefile ] || ( cd libs-$(XEN_TARGET_ARCH)/evtchn && \
+	  ln -sf $(XEN_ROOT)/tools/libs/evtchn/*.h . && \
+	  ln -sf $(XEN_ROOT)/tools/libs/evtchn/include/*.h include/ && \
+	  ln -sf $(XEN_ROOT)/tools/libs/evtchn/*.c . && \
+	  ln -sf $(XEN_ROOT)/tools/libs/evtchn/Makefile . )
 	mkdir -p libxc-$(XEN_TARGET_ARCH)
 	[ -h libxc-$(XEN_TARGET_ARCH)/Makefile ] || ( cd libxc-$(XEN_TARGET_ARCH) && \
 	  ln -sf $(XEN_ROOT)/tools/libxc/*.h . && \
@@ -350,13 +356,22 @@ libxentoollog: libs-$(XEN_TARGET_ARCH)/toollog/libxentoollog.a
 libs-$(XEN_TARGET_ARCH)/toollog/libxentoollog.a: mk-headers-$(XEN_TARGET_ARCH) $(NEWLIB_STAMPFILE)
 	CPPFLAGS="$(TARGET_CPPFLAGS)" CFLAGS="$(TARGET_CFLAGS)" $(MAKE) DESTDIR= -C libs-$(XEN_TARGET_ARCH)/toollog
 
+#######
+# libxenevtchn
+#######
+
+.PHONY: libxenevtchn
+libxenevtchn: libs-$(XEN_TARGET_ARCH)/evtchn/libxenevtchn.a
+libs-$(XEN_TARGET_ARCH)/evtchn/libxenevtchn.a: mk-headers-$(XEN_TARGET_ARCH) $(NEWLIB_STAMPFILE)
+	CPPFLAGS="$(TARGET_CPPFLAGS)" CFLAGS="$(TARGET_CFLAGS)" $(MAKE) DESTDIR= -C libs-$(XEN_TARGET_ARCH)/evtchn
+
 #######
 # libxc
 #######
 
 .PHONY: libxc
 libxc: libxc-$(XEN_TARGET_ARCH)/libxenctrl.a libxc-$(XEN_TARGET_ARCH)/libxenguest.a
-libxc-$(XEN_TARGET_ARCH)/libxenctrl.a: mk-headers-$(XEN_TARGET_ARCH) libxentoollog cross-zlib
+libxc-$(XEN_TARGET_ARCH)/libxenctrl.a: mk-headers-$(XEN_TARGET_ARCH) libxentoollog libxenevtchn cross-zlib
 	CPPFLAGS="$(TARGET_CPPFLAGS)" CFLAGS="$(TARGET_CFLAGS)" $(MAKE) DESTDIR= CONFIG_LIBXC_MINIOS=y -C libxc-$(XEN_TARGET_ARCH)
 
  libxc-$(XEN_TARGET_ARCH)/libxenguest.a: libxc-$(XEN_TARGET_ARCH)/libxenctrl.a