Thread: Reading raw device data

Greetings,

I know you can read raw data from devices in linux... But is it first in best dressed?

For example, dump.txt remains blank in the following:

Code:

#include <stdio.h>

int main(void)
{
	FILE * device, * out;
	int cc;
	
	if((device = fopen("/dev/input/mouse0", "rb")) == NULL)
	{
		perror("Failed to open the device");
		return 1;
	}

	if((out = fopen("dump.txt", "wb")) == NULL)
	{
		perror("Failed to open dump.txt");
		fclose(device);
		return 1;
	}

	while(1)
	{
		cc = fgetc(device);
		fputc(cc, out);
	}

	fclose(device);
	fclose(out);

	return 0;
}

I know my mouse is in use by X but, should I be able to read the raw data too?

What am I doing wrong?

Thanks in advance

So does your program lock up in the infinite loop, or does it exit with an error message?

Nah it locks... I just used while(1) for testing...

I've also tried

Code:

while((cc = fgetc(device)) != EOF)
	fputc(cc, out);

To no avail.

Do you know for sure whether it is looping or not?

Try capturing say the first 10 characters and then exiting.

You're not likely to ever get EOF from /dev/mouse.
Also, internal buffering may be holding on to a lot of data unless you flush the output file.

Hmm, Thought so - I read somewhere that it was FIFO, First in First Out or something. Hence my question about whether it matters because X is also reading the file.

I'm just trying to read raw mouse data... easily for that matter.

I've tried connecting 2 mice, but X reads both as one (/dev/input/mouse0 and /dev/input/mouse1).

Thanks for the help tho

Are you people quite sure about this? I can use od to dump raw mouse/keyboard data from /dev/input/mouse*, /dev/input/mice and /dev/input/event* quite easily, without interfering with X's operation at all.

Maybe it uses open() rather than fopen() ?

By shutting down X I was able to read from /dev/input/mouse0 (a lot of data, using fopen()).

However, using open() and read() worked flawlessly (both X and I get the bytes). Thanks everyone

Originally Posted by brewbuck

X uses hardware cursor acceleration, so you wouldn't notice any effect on mouse movement.

I don't get it.