CODEWITHSUNDEEP
linux-kernelkernel-moduleprocfs
Sara.0
Sara.0

Reputation: 167

How to access kernel parameters in kernel space

This is one of my lab assignments: I have to create an proc entry here: /proc/sys/kernel/ and I have to write a system call to manipulate a user space variable for different values of the proc entry I just added. For eg: say, user space variable is 1 and proc entry is 0 or 1. Now the system call should increment the user space variable by 1(if proc entry is 0/off) or multiply it by two(if proc entry is 1/on)

I did the following to add the proc entry: I created an entry xxx by adding a struct under the kernel ctl table section in the file in the kernel/sysctl.c. Compiled the kernel and the system boots well with this kernel. The entry is also added into proc directory as /proc/sys/kernel/xxx. I am now able to read or write to it from user space. I did both cat and echo to read and write resp.

I did the following in the system call: I wrote a system call to read the user space variable. I also completed and tested the access_ok, copy_from user, copy_to_user and all that. I also completed manipulating the user space variable to increment always(for now).

Problem I am facing: Now, I have to add an if condition to check the "xxx" value to decide whether I should increment or multiply the user space variable. This is where I am stuck. Not in writing the system call. I don't know how to read this proc entry "xxx".

  1. Can I use file handling?
  2. If so, should I use open() system call inside my system call? Will it work?

When I checked, there was sysctl system call, but it seems deprecated now. This IBM tutorial talks about reading the proc entry. But create_proc_entry does not apply to parameters inside /proc/sys/kernel directory right? If so, how can I ever use read proc entry function?

Upvotes: 2

Views: 1133

Answers (1)

Dipstick
Dipstick

Reputation: 10129

"But, now I have to write a system call to read the value of xxx."

I suspect that the term "system call" is being used in a formal sense and that you are being asked to add a new system call to the kernel (similar to open, read, mmap, signal etc) that returns your value.

See Adding a new system call in Linux kernel 3.3

Upvotes: 1

Related Questions