event_notifier: Make event_notifier_init_fd() #ifdef CONFIG_EVENTFD

Event notifiers are designed for eventfd(2).  They can fall back to
pipes, but according to Paolo, event_notifier_init_fd() really
requires the real thing, and should therefore be under #ifdef
CONFIG_EVENTFD.  Do that.

Its only user is ivshmem, which is currently CONFIG_POSIX.  Narrow it
to CONFIG_EVENTFD.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1458066895-20632-6-git-send-email-armbru@redhat.com>

default-configs/pci.mak

@@ -36,5 +36,5 @@ CONFIG_SDHCI=y
 CONFIG_EDU=y
 CONFIG_VGA=y
 CONFIG_VGA_PCI=y
-CONFIG_IVSHMEM=$(CONFIG_POSIX)
+CONFIG_IVSHMEM=$(CONFIG_EVENTFD)
 CONFIG_ROCKER=y

tests/Makefile

@@ -161,7 +161,7 @@ gcov-files-pci-y += hw/display/virtio-gpu-pci.c
 gcov-files-pci-$(CONFIG_VIRTIO_VGA) += hw/display/virtio-vga.c
 check-qtest-pci-y += tests/intel-hda-test$(EXESUF)
 gcov-files-pci-y += hw/audio/intel-hda.c hw/audio/hda-codec.c
-check-qtest-pci-$(CONFIG_POSIX) += tests/ivshmem-test$(EXESUF)
+check-qtest-pci-$(CONFIG_EVENTFD) += tests/ivshmem-test$(EXESUF)
 gcov-files-pci-y += hw/misc/ivshmem.c
 
 check-qtest-i386-y = tests/endianness-test$(EXESUF)

util/event_notifier-posix.c

@@ -20,11 +20,17 @@
 #include <sys/eventfd.h>
 #endif
 
+#ifdef CONFIG_EVENTFD
+/*
+ * Initialize @e with existing file descriptor @fd.
+ * @fd must be a genuine eventfd object, emulation with pipe won't do.
+ */
 void event_notifier_init_fd(EventNotifier *e, int fd)
 {
     e->rfd = fd;
     e->wfd = fd;
 }
+#endif
 
 int event_notifier_init(EventNotifier *e, int active)
 {