event notifiers are slightly generalized eventfd descriptors. Current

implementation depends on eventfd because vhost is the only user, and

vhost depends on eventfd anyway, but a stub is provided for non-eventfd

case.

We'll be able to further generalize this when another user comes along

and we see how to best do this.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

---

 Makefile.target |    1 +

 hw/notifier.c   |   50 ++++++++++++++++++++++++++++++++++++++++++++++++++

 hw/notifier.h   |   16 ++++++++++++++++

 qemu-common.h   |    1 +

 4 files changed, 68 insertions(+), 0 deletions(-)

 create mode 100644 hw/notifier.c

 create mode 100644 hw/notifier.h

diff --git a/Makefile.target b/Makefile.target

index 6037fed..0c844a9 100644

--- a/Makefile.target

+++ b/Makefile.target

@@ -167,6 +167,7 @@ obj-y = vl.o async.o monitor.o pci.o pci_host.o pcie_host.o machine.o gdbstub.o

 # virtio has to be here due to weird dependency between PCI and virtio-net.

 # need to fix this properly

 obj-y += virtio-blk.o virtio-balloon.o virtio-net.o virtio-pci.o virtio-serial-bus.o

+obj-y += notifier.o

 obj-$(CONFIG_KVM) += kvm.o kvm-all.o

 # MSI-X depends on kvm for interrupt injection,

 # so moved it from Makefile.hw to Makefile.target for now

diff --git a/hw/notifier.c b/hw/notifier.c

new file mode 100644

index 0000000..dff38de

--- /dev/null

+++ b/hw/notifier.c

@@ -0,0 +1,50 @@

+#include "hw.h"

+#include "notifier.h"

+#ifdef CONFIG_EVENTFD

+#include <sys/eventfd.h>

+#endif

+

+int event_notifier_init(EventNotifier *e, int active)

+{

+#ifdef CONFIG_EVENTFD

+	int fd = eventfd(!!active, EFD_NONBLOCK | EFD_CLOEXEC);

+	if (fd < 0)

+		return -errno;

+	e->fd = fd;

+	return 0;

+#else

+	return -ENOSYS;

+#endif

+}

+

+void event_notifier_cleanup(EventNotifier *e)

+{

+	close(e->fd);

+}

+

+int event_notifier_get_fd(EventNotifier *e)

+{

+	return e->fd;

+}

+

+int event_notifier_test_and_clear(EventNotifier *e)

+{

+	uint64_t value;

+	int r = read(e->fd, &value, sizeof value);

+	return r == sizeof value;

+}

+

+int event_notifier_test(EventNotifier *e)

+{

+	uint64_t value;

+	int r = read(e->fd, &value, sizeof value);

+	if (r == sizeof value) {

+		/* restore previous value. */

+		int s = write(e->fd, &value, sizeof value);

+		/* never blocks because we use EFD_SEMAPHORE.

+		 * If we didn't we'd get EAGAIN on overflow

+		 * and we'd have to write code to ignore it. */

+		assert(s == sizeof value);

+	}

+	return r == sizeof value;

+}

diff --git a/hw/notifier.h b/hw/notifier.h

new file mode 100644

index 0000000..24117ea

--- /dev/null

+++ b/hw/notifier.h

@@ -0,0 +1,16 @@

+#ifndef QEMU_EVENT_NOTIFIER_H

+#define QEMU_EVENT_NOTIFIER_H

+

+#include "qemu-common.h"

+

+struct EventNotifier {

+	int fd;

+};

+

+int event_notifier_init(EventNotifier *, int active);

+void event_notifier_cleanup(EventNotifier *);

+int event_notifier_get_fd(EventNotifier *);

+int event_notifier_test_and_clear(EventNotifier *);

+int event_notifier_test(EventNotifier *);

+

+#endif

diff --git a/qemu-common.h b/qemu-common.h

index 5fbe0f9..cdead98 100644

--- a/qemu-common.h

+++ b/qemu-common.h

@@ -217,6 +217,7 @@ typedef struct uWireSlave uWireSlave;

 typedef struct I2SCodec I2SCodec;

 typedef struct DeviceState DeviceState;

 typedef struct SSIBus SSIBus;

+typedef struct EventNotifier EventNotifier;

 /* CPU save/load.  */

 void cpu_save(QEMUFile *f, void *opaque);

-- 

1.6.6.144.g5c3af