[Xenomai] Transfer data from a kernel module to user

[Xenomai] Transfer data from a kernel module to user

[ashwin damle]

Hello Developers,

I am trying to pass data from the Xenomai kernel module, using RTDM driver,
to a user program. I am using the default examples-tut01-skeleton-drv.c and
tut01-skeleton-app.c. The examples are working nicely  and I could get the
right expected results. I am using Linux raspberrypi 3.5.7-xenomai #4
PREEMPT Tue Mar 11 16:49:44 IST 2014 armv6l GNU/Linux, Xenomai used for
during compilation was xenomai-2.6.2.1. The target is RaspberryPi.

The intention is to transfer a integer variable from the kernel to user. I
tried changing the default example program only to reeive the error message
""ERROR : can't copy data from driver". I am unable to figure-out the
problem. Attach is the program which I edited. I have written a comment
wherever I define my variable, which is freq. Below is a snap

"
static ssize_t simple_rtdm_read_nrt(struct rtdm_dev_context *context,
                    rtdm_user_info_t * user_info, void *buf,
                    size_t nbyte)
{
    buffer_t * buffer = (buffer_t *) context->dev_private;
    int size = (buffer->size > nbyte) ? nbyte : buffer->size;

    buffer->size = sizeof(buffer->freq);
    buffer->freq = 50;            //my variable, this is printed correctly
as seen in dmesg

    if (rtdm_safe_copy_to_user(user_info, buf, &buffer->freq,
sizeof(buffer->freq)))
        rtdm_printk("ERROR : can't copy data from driver\n");

    return size;
}
"
Attached is the user program, too.

Also, I wanted to know whether it is explicitly required to write to the
device before reading it? I only want to read the device.( My application
is noting the time of GPIO interrupts. )

Could you please help me with this? Request you to help me solve the
problem.

Thanks.
Ashwin

-- 

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Re: [Xenomai] Transfer data from a kernel module to user

[Gilles Chanteperdrix]

On 03/14/2014 10:52 AM, ashwin damle wrote:
> Hello Developers,
> 
> I am trying to pass data from the Xenomai kernel module, using RTDM driver,
> to a user program. I am using the default examples-tut01-skeleton-drv.c and
> tut01-skeleton-app.c. The examples are working nicely  and I could get the
> right expected results. I am using Linux raspberrypi 3.5.7-xenomai #4
> PREEMPT Tue Mar 11 16:49:44 IST 2014 armv6l GNU/Linux, Xenomai used for
> during compilation was xenomai-2.6.2.1. The target is RaspberryPi.
> 
> The intention is to transfer a integer variable from the kernel to user. I
> tried changing the default example program only to reeive the error message
> ""ERROR : can't copy data from driver". I am unable to figure-out the
> problem. Attach is the program which I edited. I have written a comment
> wherever I define my variable, which is freq. Below is a snap
> 
> "
> static ssize_t simple_rtdm_read_nrt(struct rtdm_dev_context *context,
>                     rtdm_user_info_t * user_info, void *buf,
>                     size_t nbyte)
> {
>     buffer_t * buffer = (buffer_t *) context->dev_private;
>     int size = (buffer->size > nbyte) ? nbyte : buffer->size;
> 
>     buffer->size = sizeof(buffer->freq);
>     buffer->freq = 50;            //my variable, this is printed correctly
> as seen in dmesg
> 
>     if (rtdm_safe_copy_to_user(user_info, buf, &buffer->freq,
> sizeof(buffer->freq)))
>         rtdm_printk("ERROR : can't copy data from driver\n");
> 
>     return size;
> }
> "
> Attached is the user program, too.
> 
> Also, I wanted to know whether it is explicitly required to write to the
> device before reading it? I only want to read the device.( My application
> is noting the time of GPIO interrupts. )
> 
> Could you please help me with this? Request you to help me solve the
> problem.

copy_to_user operates on addresses, so you should pass &freq instead of
(void *)freq to rt_dev_read, otherwise the current value of freq, which
is a random value, is used by copy_to_user as an address which causes a
fault.


-- 
                                                                Gilles.

Re: [Xenomai] Transfer data from a kernel module to user

[Gilles Chanteperdrix]

On 03/14/2014 03:13 PM, ashwin damle wrote:
> Hi Gilles,
>
> I got it working. Thanks for your help. I am very grateful to you. You
> responded really fast.
>
> There is one more small doubt. I want the kernel module to run with
> highest priority. I saw the APIs for setting priority but they refer to
> rtdm_task_init() which is not used in my program tut01-skeleton-drv.c-so
> how do I set priority?

You do not seem to understand much about C and kernel modules 
programming. I suggest you read some documentation, or buy some training 
on C language programming. When you are done, read the "Linux device 
drivers" book:

https://lwn.net/Kernel/LDD3/

Then come back to Xenomai, and start by reading the documentation here:
http://xenomai.org/index.php/Included_documentation_summary

Please do not send me private messages.

-- 
					    Gilles.

Re: [Xenomai] Transfer data from a kernel module to user

[ashwin damle]

Hello Gilles,

Yes, you are correct.

Sorry to bother you with trivial questions. I will start reading the
documentation you mentioned. Also, the e-mail sent to you was not
intentional. Sorry again.

Thanks for your help.

Ashwin


On 14 March 2014 21:11, Gilles Chanteperdrix <
gilles.chanteperdrix@xenomai.org> wrote:

> On 03/14/2014 03:13 PM, ashwin damle wrote:
>
>> Hi Gilles,
>>
>> I got it working. Thanks for your help. I am very grateful to you. You
>> responded really fast.
>>
>> There is one more small doubt. I want the kernel module to run with
>> highest priority. I saw the APIs for setting priority but they refer to
>> rtdm_task_init() which is not used in my program tut01-skeleton-drv.c-so
>> how do I set priority?
>>
>
> You do not seem to understand much about C and kernel modules programming.
> I suggest you read some documentation, or buy some training on C language
> programming. When you are done, read the "Linux device drivers" book:
>
> https://lwn.net/Kernel/LDD3/
>
> Then come back to Xenomai, and start by reading the documentation here:
> http://xenomai.org/index.php/Included_documentation_summary
>
> Please do not send me private messages.
>
> --
>                                             Gilles.
>

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