>>> On Mon, May 14, 2007 at 3:12 PM, in message
<[EMAIL PROTECTED]>, Davide Libenzi
<[EMAIL PROTECTED]> wrote:
> On Mon, 14 May 2007, Gregory Haskins wrote:
>
>> >>> On Mon, May 14, 2007 at 1:23 PM, in message <[EMAIL PROTECTED]>,
>> Avi Kivity <[EMAIL PROTECTED]> wrote:
>> >
>> >> Do you close the signaled fd after receiving the signal/event? If you
>> >> don't close it, eventfd will always return ready (POLLIN).
>> >>
>> >
>> > We don't. Anyway, that's what we thought. Thanks for the confirmation.
>> >
>>
>> And plus I just finished converting to Davide's eventfd, so its moot ;)
>>
>> On that topic, I could use some advice:
>>
>> I was originally planning on adding a new ioctl like KVM_VCPU_CREATE_EVENTFD
> which would allocate a new eventfd and return it. However, I soon realized
> that the only method to create an eventfd is sys_eventfd(), which is not
> exported by the eventfd.h headerfile (presumably this must be a new system
> call).
>>
>> So based on that, I figured I would change the model so that the usermode
> app should call the eventfd open() call on its own, and then they could
> register the fd with me. So KVM_VCPU_CREATE_EVENTFD becomes
> KVM_VCPU_SET_EVENTFD (where - 1 "unregisters" it).
>>
>> Does this sound like a reasonable approach? If so, how does the usermode
> app actually open the eventfd today? Is there a new glibc that I need to get
> the new system call? Or can the app use open() somehow? If open(), what is
> the path that should be specified?
>>
>> Conversely, if my first approach was the right one how do I invoke the
> sys_eventfd()? Is there a way to invoke system calls in kernel mode? A
> better way?
>>
>> Any advice appreciated.
>
> The eventfd syscall is defined in include/linux/syscalls.h
> From userspace, till glibc aligns:
>
> #include <sys/syscall.h>
>
> #ifndef __NR_eventfd
> #if defined(__x86_64__)
> #define __NR_eventfd 283
> #elif defined(__i386__)
> #define __NR_eventfd 323
> #else
> #error Cannot detect your architecture!
> #endif
> #endif
>
> static int eventfd(int count) {
>
> return syscall(__NR_eventfd, count);
> }
>
>
> If the kernel side receives an fd from userspace, it must use:
>
> file = eventfd_fget(fd);
> if (IS_ERR(file))
> ....
> eventfd_signal(file, 1);
> fput(file);
>
>
>
> - Davide
Thanks Davide,
That is very helpful. Is there any reason why we can't export
eventfd_signal() and eventfd_fget() to modules?
-Greg
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