Messages in this thread | | | Date | Fri, 3 Dec 2004 21:15:36 +0100 | From | Sylvain <> | Subject | Re: distinguish kernel thread / user task |
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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 > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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