[uml-devel] Regarding getpid

[uml-devel] Regarding getpid

[Krishnappa Abhijith-A21204]

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Hi ,
            "Process system calls must be nullified in the host, and
this is done by converting them into getpid. "
How is system calls  are nullified by converting them to getpid() ?
 
Pls let me know.
 
Regards,
Abhi

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Re: [uml-devel] Regarding getpid

[Geert Uytterhoeven]

On Tue, 12 Dec 2006, Krishnappa Abhijith-A21204 wrote:
>             "Process system calls must be nullified in the host, and
> this is done by converting them into getpid. "
> How is system calls  are nullified by converting them to getpid() ?

Instead of calling the actual system call, it just calls getpid(). I.e. the
actual system call is not executed, and getpid() is more or less a NOP.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

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Re: [uml-devel] Regarding getpid

[Krishnappa Abhijith-A21204]

Ok Thanks. So actually getpid() doesn't cause mode switch.
But is it mandatory to execute  getpid()? If yes why

Regards,
Abhi

-----Original Message-----
From: geert@sonytel.be [mailto:geert@sonytel.be] On Behalf Of Geert
Uytterhoeven
Sent: Tuesday, December 12, 2006 3:19 PM
To: Krishnappa Abhijith-A21204
Cc: User-mode Linux Kernel Development
Subject: Re: [uml-devel] Regarding getpid

On Tue, 12 Dec 2006, Krishnappa Abhijith-A21204 wrote:
>             "Process system calls must be nullified in the host, and 
> this is done by converting them into getpid. "
> How is system calls  are nullified by converting them to getpid() ?

Instead of calling the actual system call, it just calls getpid(). I.e.
the actual system call is not executed, and getpid() is more or less a
NOP.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker.
But when I'm talking to journalists I just say "programmer" or something
like that.
							    -- Linus
Torvalds

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Re: [uml-devel] Regarding getpid

[Jeff Dike]

On Tue, Dec 12, 2006 at 06:12:24PM +0800, Krishnappa Abhijith-A21204 wrote:
> Ok Thanks. So actually getpid() doesn't cause mode switch.

Sure it does.  Any system call does.

> But is it mandatory to execute  getpid()? If yes why

That's the way ptrace traditionally works.  PTRACE_SYSEMU, which came later
avoids the need to invoke some system call.  It just nullifies the system
call in the expectation that the tracer will emulate it.

				Jeff

-- 
Work email - jdike at linux dot intel dot com

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