Question

I have an assignment in my Operating Systems class to make a simple pseudo-stack Linux device driver. So for an example, if I was to write “Hello” to the device driver, it would return “olleH” when I read from it. We have to construct a tester program in C to just call upon the read/write functions of the device driver to just demonstrate that it functions in a FILO manner. I have done all of this, and my tester program, in my opinion, demonstrates the purpose of the assignment; however, out of curiosity, inside BASH I execute the following commands:

echo “Test” > /dev/driver

cat /dev/driver

where /dev/driver is the special file I created using “mknod”. However, when I do this, I get a black screen full of errors. After I swap back to the GUI view using CNTRL+ALT+F7, I see that BASH has returned “Killed”.

Does anyone know what could be causing this to happen? I am confused since my tester program calls open(), read(), and write() with everything functioning as it should.

If I need to show some code, just ask.

Answer 1

The function in your device driver that writes to the buffer you are providing it is most likely causing this issue.

To debug, you can do the following:

• First, make sure the read part is fine. You can printk your internal buffer after you read from input to ensure this.

• Second, in your write function, printk some information instead of actually writing anything and make sure everything is fine.

Also, make sure the writer makes it clear that the write has ended. I’m not particularly sure about device drivers, but you either need to return 0 as the number of bytes written when called a second time, or set an eof variable (if that is one of the arguments to your function)