Date: Thu, 22 Dec 2011 07:57:11 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Sushanth Rai <sushanth_rai@yahoo.com> Subject: Re: Using kevent for signalling user app from kernel Message-ID: <201112220757.11823.jhb@freebsd.org> In-Reply-To: <1324533811.54730.YahooMailClassic@web180006.mail.gq1.yahoo.com> References: <1324533811.54730.YahooMailClassic@web180006.mail.gq1.yahoo.com>
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On Thursday, December 22, 2011 1:03:31 am Sushanth Rai wrote:
> Hi,
>
> I'm planning to use kqueue/kevent mechanism to notify a user application
from the kernel. Basically I set up a file descriptor for read event from the
user application by calling kevent(). Now, I would like to wake-up the process
from within the kernel. The wake-up will happen due to one of the internal
events (not due to data being available to read). I have access to the process
structure and vnode corresponding to file descriptor. Is there a mechanism
available from the kernel to trigger a wakeup and clear the kernel break
notify message ?
In the kernel you'd typically use KNOTE() to signal that an event should be
signalled. However, that will only post the event if the file is now
readable. I think you have a couple of options:
1) You can send a signal to the process which will interrupt the kevent.
2) You can add a new filter type and use it with your file descriptor to
signal your special side-band events. The userland app will have to add
both an EVFILT_READ event and and event for your custom filter type.
You can then use KNOTE when your side-band event happens and your custom
filter's f_event hook can signal the event in that case.
--
John Baldwin
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