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

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Feb 25, 2010 at 01:22:04PM -0600, Anthony Liguori wrote:
> 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?

No, nonblocking eventfd read never returns EINTR.


>> +}
>> +
>> +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;
>>
>>    
>
>