Re: distinguish kernel thread / user task

[Sylvain <autofr@gmail.com>]

I am trying to do a tool to record task switching...separating also
kernel/user tasks, but I got some trouble with that last case.

I confused since "ps" is actually able to distinguish kernel thread
from user task.
I wouldn't had a flag if It 's not necessary

Sylvain


On Fri, 03 Dec 2004 14:24:27 -0500, Brian Gerst <bgerst@didntduck.org> wrote:
> Sylvain wrote:
> 
> 
> > Hi all,
> >
> > I have little question while doing some kernel implementation.
> > How can I distinguish whether a task_struct is actually kernel thread
> > or mere user task?
> >
> > My idea was to look at task_struct "mm" field to discriminate them,
> > but that was wrong...
> >
> > Thanks,
> >
> > Sylvain
> 
> To the scheduler, a thread is a thread.  It doesn't care if it's a
> kernel thread or not.  The difference is execution context, which is
> cpu-dependant.  For example, on x86 the difference is in the code
> segment the task runs in.  Kernel threads run in KERNEL_CS (ring 0), and
> user threads run USER_CS (or any other ring 3 code segment, or vm86 mode
> set in eflags).  Other cpus might have a flag in the status register.
> 
> What are you trying to do that you need to know whether a thread is
> kernel or user?  I suppose if there were a compelling enough reason, a
> kernel/user flag could be added to the task struct, set in do_fork() for
> kernel threads, and cleared by execve().
> 
> --
>                                Brian Gerst
>