System Calls 📞☎️
How do apps interact with Kernel?
using system calls.
What are system calls?
- System calls are special functions that allow user-level programs to request services or resources from the operating system's kernel. Since programs running in user space don't have direct access to hardware or core system resources, they rely on system calls to perform tasks that require privileged access, like reading files, allocating memory, or communicating with hardware.
System Calls are the only way through which a process can go into kernel mode from user mode.- Transitions from
UserModetoKernelModedone by software interrupts. - System Calls are implemented in C and Assembly language.
Example:
-
Eg.
mkdir my_dir- Mkdir indirectly calls kernel and asked the file mgmt. module to create a new directory.
- Mkdir is just a wrapper of actual system calls.
- Mkdir interacts with kernel using system calls.
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Eg.
Creating a process- User executes a process. (User space)
- Gets system call. (US)
- Exec system call to create a process. (KS)
- Return to user space.
Types of System Calls:
FAQs 🙋♂️
Q.1: What is the purpose of System Calls?
The purpose of the system calls is to allow user-level applications access of the services provided by the kernel. The user apps do not have the privilege to perform operations, so they make system calls which further requests a kernel to provide a specific service.
Q.2: How do device management System Calls work?
Device management system calls work by allowing a certain process or a device interact and get access to other hardware resources and perform various operations.
Q.3: What is user mode and kernel mode?
User mode and kernel modes are two different privilege modes of a Computer System, that separates the execution of operations by the user applications and the kernel on hardware. This separation provides security, stability, and a level of control over system resources.
Q.4: What happens when a System Call is executed?
When a system call is executed, a context switch occurs and the computer system switches from user mode to kernel mode and now the kernel performs the desired operation.
Q.5: What is a software interrupt?
A software interrupt is a mechanism through which the OS performs a context switch and transition from user mode to kernel mode. A software interrupt use is not limited only to the system calls but it can also be made when a high priority task is required to be executed by the CPU.