What is difference between kernel API and system call ?

[leetow2003]

Are they in the same layer kernel?do they call each other?
What is difference between them?

[dozniak]

Kernel API is a set of services provided by the kernel.

System call is one of the ways to invoke the kernel API functions.

[leetow2003]

Kernel API is a set of services provided by the kernel.

System call is one of the ways to invoke the kernel API functions.

Are they in the same kernel layer?

[zhiayang]

Kernel API is a set of services provided by the kernel.

System call is one of the ways to invoke the kernel API functions.

Are they in the same kernel layer?

The Kernel API includes things that require access to such things, such as raw disk access (which would be processed by the FS driver and so on), starting a process etc.

Such API functions are usually exposed through system calls.
The call handler is usually in ring 0 along with the kernel, although your design may vary.

[bluemoon]

syscall usually refer to interface that exposes to user space applications or drivers, as the interface for external entity to interact with the system.

Kernel API has no specific meaning, it depends on which context you are talking, it can be components for kernel developers, driver interfaces, or syscall, etc.

[leetow2003]

Could they call each other?could you give me an example?

[dozniak]

Could they call each other?could you give me an example?

Could functions call each other? They certainly can.

You must understand the meaning of the three-letter acronym "API". It means "application programming interface", i.e. it's a bunch of functions that your application can call.

For example, the VFS API consists of "open", "close", "read", "write", "seek" calls which your application can use to open, close,read and write files.

What relation does it have to the system call? Well, "open" could be implemented as a system call. It can also be implemented as an RPC to the VFS server. It can also be implemented as a direct function call. Therefore your question about "can kernel API and system call call each other?" makes no sense.

[Jezze]

Perhaps a syscall more reflects the kernel ABI rather?

[iansjack]

Could they call each other?could you give me an example?

This is beginning to sound a lot like a homework question.