Re: [Xenomai-help] Sharing Semaphores in Kernel and User Space

[Jan Kiszka <jan.kiszka@domain.hid>]

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Jonathan Haws wrote:
>>> I am writing a driver that needs to wake up a user space thread on
>> a
>>> hardware interrupt.  I am reading about the Xenomai APIs
>> semaphores
>>> and want to know if I create a semaphore in my kernel module with
>> a
>>> given name using rt_sem_create, can I call rt_sem_bind in user
>> space
>>> to bind to that same semaphore?
>>>
>>> I am sure hoping the answer is yes!
>> The answer is yes, but...
>> this programming model is deprecated. You should be implementing a
>> driver using the RTDM API, as you would do with Linux.
> 
> The driver is a really dumb driver - all it really does is setup pointers to the PCI BARs and installs the interrupt.  I provide an mmap routine to map the BARs to user space so I can control the device from there.
> 
> Would this still be necessary to use the RTDM API?  I guess to install the interrupt, but there really is not anything else the driver does.

Abstraction is the primary job of a driver. Pushing things to user space
quickly blurs the boundaries and ends up in tricky to maintain blob on
the long term.

> 
> I was also reading the RTDM API and am confused about the rtdm_iomap_to_user() function - is that to be called from my user space application and it will then call the mmap routine that I have in place for my driver?

It's part of the function set that a driver can use, not an application.
This function will do all the work required to let some I/O memory show
up in the user space's memory range.

Jan


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