How does user space and kernel space communicate?

How does user space and kernel space communicate?

There are couple of well known methods to communicate from user space to kernel space.

1. Virtual file system like /proc , /sys , /configfs , /debugfs Standard.
2. system call like read() , write() , open() , close() , fork()
3. ioctl for char drivers.
4. netlink socket – mostly used by network subsystem.

How do processes communicate with kernel?

There is no separate “kernel” process to communicate with. The kernel is code that runs in the context of any process. Kernel kernel code is invoked by an interrupt, trap, or exception. While in kernel mode the process has access to the kernel memory that is shared by all processes.

What is mac80211 in Linux?

mac80211 is a framework which driver developers can use to write drivers for SoftMAC wireless devices. SoftMAC devices allow for a finer control of the hardware, allowing for 802.11 frame management to be done in software for them, for both parsing and generation of 802.11 wireless frames.

What is netlink socket?

The Netlink socket family is a Linux kernel interface used for inter-process communication (IPC) between both the kernel and userspace processes, and between different userspace processes, in a way similar to the Unix domain sockets.

What is Copy_to_user in Linux?

The copy_to_user function copies a block of data from the kernel into user space. This function accepts a pointer to a user space buffer, a pointer to a kernel buffer, and a length defined in bytes. The function returns zero on success or non-zero to indicate the number of bytes that weren’t transferred.

What is Wiphy?

The fundamental structure for each device is the ‘wiphy’, of which each instance describes a physical wireless device connected to the system.

What is Netlink H?

Netlink is used to transfer information between the kernel and user-space processes. It consists of a standard sockets-based interface for user space processes and an internal kernel API for kernel modules.

What causes a context switch from userspace to kernel space?

System calls (which includes accessing devices) also causes a context switch from userspace to kernel space.

What is the kernel module used for?

This kernel module needs to receive tasks issued by a user space program, and send results back to user space program after completion. The user space program should be blocked while the kernel module is doing its job.

How to communicate between two userspace programs in a module?

The easiest is to use the proc file interface to communicate, especially if the message and the result are less than one page in size. Open and close can implement locking so that only one instance of userspace program can actually access the module request engine.