Re: How to define customized notification from kernel-space to user-space
Re: How to define customized notification from kernel-space to user-space
- Subject: Re: How to define customized notification from kernel-space to user-space
- From: Jeff Moore <email@hidden>
- Date: Tue, 10 Feb 2009 11:53:54 -0800
This is a question more for the IOKit list I think. Basically, you
need to implement a custom user-client object for the object in your
driver you wish to send messages from.
I'll tell you what I know, but you should seek advice from the
experts. They may even be able to point you at some sample code for
what I'm about to describe.
At any rate, the outline for what it takes for a driver to send a
notification to user-space goes like this:
In the driver:
1) Create a new sub-class of IOUserClient. You will want to override
registerNotificationPort() along with some of the housekeeping methods
like initWithTask(), free(), start(), getService(), clientClose(), etc.
2) In your override of IOUserClient::registerNotificationPort(), you
can store the port somewhere handy. registerNotificationPort() is
called when a user-space entity calls IOConnectSetNotificationPort().
This port is the one on which the user-client wants to receive the
service's notifications.
3) In your sub-class of IOService, you have to override
newUserClient(). This is the function that gets called to instantiate
a new user-client object when a user-space entity has called
IOServiceOpen() on your IOService. Since the IOService you will likely
use is a sub-class of an IOAudio family class, you will need to pick a
value for the user-client type that doesn't conflict with the IOAudio
family (which uses 0, I believe).
4) Your sub-class of IOService should also override user-client
housekeeping methods like handleClose().
5) When you want to send a notification to the user-space entity, just
build up the message header and payload and call
mach_msg_send_from_kernel() to dispatch the message to the port that
the user-space entity has registered.
Out in user-space:
1) Allocate a mach port that will receive the messages from the
kernel. However you set up the port, be sure that it is capable of
receiving messages. I use a CFMachPort for this job, generally
speaking, because it handles the messy details of creating a
CFRunLoopSource I can add to a thread so that the port an receive
messages.
2) Locate the IOService you want to receive a notification from using
IOServiceMatching() or some other IORegistry mechanism.
3) Open a connection to the service by calling IOServiceOpen(). Be
sure to pass the same user-client type that your service is using.
4) Tell the service what port to send messages to by calling
IOConnectSetNotificationPort().
Obviously, this is glossing over a lot of details in both the driver
side and user-space side of things. But it should give you an idea
about what sort of work you need to do so that you can seek further
guidance.
On Feb 10, 2009, at 2:31 AM, David Tan wrote:
I’m working on an audio driver and want to implement a customized
notification. My audio device will report some status code to my
KEXT during runtime.
After the KEXT has captured a status code, I need a mechanism to
notify the user-space application at real time.
So far, it seems only I can do is to setup a thread in user-space
application and querying the KEXT periodically via IOUserClient.
That I don’t think is the best approach. I wonder if there’s a
notification mechanism to simplify it.
After doing some searching in Apple’s Mailing list, it seems I can
use Mach Port to achieve it. However, I cannot find detailed
information of this solution. Does anyone here can give me some tips
or advices?
Any ideas will be much appreciated. Thanks a lot!
--
Jeff Moore
Core Audio
Apple
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