On Sat, Aug 2, 2014 at 4:58 PM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
> On 07/31/14 18:07, Aniroop Mathur wrote:
>> Dear IIO Community,
>> Greetings !!
>>
>> I am Aniroop Mathur working in Sensors kernel and HAL field.
>> I have one question about IIO, for which i need your support.
>>
>> I would like to open two file descriptors for IIO device node - /dev/iio:device0
>> int fd1 = open("/dev/iio:device0",O_RDONLY);
>> int fd2 = open("/dev/iio:device0",O_RDONLY);
>>
>> But, only first open call succeeds.
>> The second open calls fails with error "Device or Resource busy".
>>
>> In normal input device, we can open as many event node file
>> descriptors as we like.
>> int fd1 = open("/dev/input/event1");
>> int fd2 = open("/dev/input/event1");
>>
>> Both calls succeeds for input subsystem case.
>>
>> So, why restriction is present in IIO subsystem ?
> Basically a different design descision for the userspace interfaces. Input moves
> a lot of handling and processing into the kernel. For IIO, which at least sometimes
> is dealing with much faster devices, this adds overhead. Note that we remove
> all overhead of description of data from the main data stream to reduce overhead
> so that must be described elsewhere (sysfs).
>
> If you really want to do that then we do have a prototype input client driver for IIO
> (though it's not seen much work recently).
>
I did not understood your point clearly. (prototype input client driver for IIO)
So you mean it is possible to open same iio device node twice by some means ?
If so, could you please explain how to do it ?
Actually, main aim is to create an IIO device Simulator.
For this I need to write data to IIO device node from a user space application
when hardware chip is actually off.
So, even after opening iio device node,
can we write the data to IIO device node from user space ?
(I do not see write function in below fileops)
static const struct file_operations iio_event_chrdev_fileops = {
.read = iio_event_chrdev_read,
.poll = iio_event_poll,
.release = iio_event_chrdev_release,
.owner = THIS_MODULE,
.llseek = noop_llseek,
};
> In theory it is possible to have more userspace exposed buffer associated with
> a given IIO device, though right now this isn't actually done. The intent of that
> infrastructure is to provide splitting of data to multiple users within the kernel
> (one might be IIO, another input and a third battery monitoring).
>
> Ultimately if you want multiple userspace devices to share a datastream, then it
> makes sense to avoid multiple switches in and out of the kernel and do it in userspace
> instead.
>
> Jonathan
>
>> Why two iio device nodes cannot be open together ?
> Not quite what I think you mean. You mean, why can you not open the same device node
> twice?
Yes, right. Thanks for the correction. :)
>>
>> Thanks in advance !
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Thanks,
Aniroop Mathur
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