Hi ,

I have the following requirement in my module.
The driver gets some data from the external device. After getting 1MB of data it has to send it to the user space application.

What is the best thing to implement for this in driver.?

Is it ok to implement like, after getting data, the driver will send a signal to the user space application. Then the user space application sends an ioctl to read the data.

Is there any alternate, that the driver directly sends the data without the user space application asks for it.? I dont think its feasible, but just asking if I missed something.

Thanks in advance.

Sunil.

The usual way for something like this is a standard UNIX I/O call. User space starts everything in motion. For example it issues a read to your driver which passes in the address of a 1 MB memory buffer. The user space program is now sleeping waiting for the kernel to respond. The driver puts the data into the memory buffer and then completes the I/O. This wakes up the waiting user space program which now has its 1 MB of data.

Doing it the other way around as you propose has a number of problems. What if there are two user space programs? What if there are multiple devices? What if the user space program has stopped running? What if you get less than 1 MB? How do you tell user space if the device got an error? All of these are handled by the standard way of doing things, none of them are if you make up your own way.

Hi smallpond,
Thanks a lot for your feedback.

can you please brief me the i/o call you mentioned.
You mean I need to use read system call for this from user application or do I need
to use any ioctl.
Does the user application sleeps itself after initiating the read or we need to call any sleep function.
I dont know if it is very basic as I am not familiar with linux.

Please help me.

Regards,
Sunil.

The user-space program(s) always need to "rendezvous" with the kernel-space through some kind of call which it makes. "ioctl()" or an asynchronous read is what is normally used.

This is not a Linux question, this is an Operating System question. Applications run in user space. The kernel provides services. This is true in all environments. Read "Linux Device Drivers" for a description of how the two communicate.