[Qemu-devel] Re: [PATCHv2 03/12] notifier: event notifier implementation

[Anthony Liguori <anthony@codemonkey.ws>]

On 02/25/2010 12:28 PM, Michael S. Tsirkin wrote:
> 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 4c4d397..c1580e9 100644
> --- a/Makefile.target
> +++ b/Makefile.target
> @@ -173,6 +173,7 @@ 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-y += rwhandler.o
>   obj-$(CONFIG_KVM) += kvm.o kvm-all.o
>   obj-$(CONFIG_ISA_MMIO) += isa_mmio.o
> 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;
>    

Probably should handle EINTR, no?

> +}
> +
> +int event_notifier_test(EventNotifier *e)
> +{
> +	uint64_t value;
> +	int r = read(e->fd,&value, sizeof value);
>    

Coding Style is not quite explicit here but we always use 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 @@
>    

Needs copyright/license.

Thanks for doing this abstraction, I'm really happy with it over direct 
eventfd usage.

Regards,

Anthony Liguori

> +#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 805be1a..f12a8f5 100644
> --- a/qemu-common.h
> +++ b/qemu-common.h
> @@ -227,6 +227,7 @@ typedef struct uWireSlave uWireSlave;
>   typedef struct I2SCodec I2SCodec;
>   typedef struct DeviceState DeviceState;
>   typedef struct SSIBus SSIBus;
> +typedef struct EventNotifier EventNotifier;
>
>   typedef uint64_t pcibus_t;
>
>