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Old 08-04-2009, 11:48 PM   #1
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difference between kthread_create(), kernel_thread()

I am new to linux kernel programming...

As I heard in linux kernel there is no special handling for threads, all threads will be treaded like processes.

I want to just create threads in kernel mode and try to access global memory by writing a kernel module which will be loaded at run time using insmod.
To have kernel thread, I am getting two functions those are kthread_create()and kernel_thread(). what is the difference between these functions.what are all the resources shared for child process(thread) if we create using above functions.

What is the procedure to create a new process which is independent of parent process.
Old 08-05-2009, 10:52 PM   #2
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You're actually mixing two entirely-separate concepts here. (It's okay... the names are confusingly similar!)

"The kernel" lives in the highest-heavens of the computer. It creates the environment in which all user-level processes run. It knows about all processes, and all threads within those processes, and "it gives them life." But in so doing, it does not ... actually cannot ... play by their rules. It does not have access, itself, to the programming facilities that it affords to the user-land threads and processes which run under its benevolent tutelage.

Well ... somewhere along the way, some kernel-programmer thought that this was rather an unfair limitation. It occurred to this person that many of the essential tasks that the kernel performs can most-easily be thought of in terms of "threads," which are dispatched much like ordinary user-land threads but which run entirely in kernel-space. Such threads are, in other words, "entirely part of the kernel ... entirely divine..." but they are also "threads" and therefore capable of doing the things that threads can do. Things like "waiting," and "doing I/O," and so-on.

Typical example? How about "the virtual-memory swapper?" When you set about to describe how it works and what it does, you might find yourself saying that it ... waits for the amount of available memory to drop, then scans through (and locks...) virtual memory segments and performs I/O to move them out to disk ... and signals other threads, and ... you get the idea. All of these things, are things that threads can quite-naturally do.

But what if "'the kernel' can't do what threads do?"

The obvious answer is: "figure out a way for 'the kernel' to be able to support 'threads!'" So... somebody did.

A "kernel thread," then, is a thing which the kernel actually can "dispatch," under most (but not all) of the usual rules and conditions that apply to "threads," but which is nevertheless a fully-privileged part of "the kernel." It is an asynchronous "part of the kernel."

Ponder that for a while . . .

Last edited by sundialsvcs; 08-05-2009 at 10:59 PM.


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