changing internal kernel system mechanism in runtime by a module patch

changing internal kernel system mechanism in runtime by a module patch

[Yitzchak Eidus]

is it possible to replace linux kernel internal functions such as
schdule () to lets say my_schdule ()  in a run time with a module
patch???
(so that every call in the kernel to schdule() will go to my_schdule()... ) ???

i am talking about a clean/standard way to do such thing
(without overwrite the mem address of the function and replace it in a
dirty way...)

Re: changing internal kernel system mechanism in runtime by a module patch

[Adrian Bunk]

On Thu, Nov 16, 2006 at 09:19:50PM +0200, Yitzchak Eidus wrote:
> is it possible to replace linux kernel internal functions such as
> schdule () to lets say my_schdule ()  in a run time with a module
> patch???
> (so that every call in the kernel to schdule() will go to my_schdule()... ) 
> ???
> 
> i am talking about a clean/standard way to do such thing
> (without overwrite the mem address of the function and replace it in a
> dirty way...)

No.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

Re: changing internal kernel system mechanism in runtime by a module patch

[Jan Engelhardt]

On Nov 16 2006 20:29, Adrian Bunk wrote:
>On Thu, Nov 16, 2006 at 09:19:50PM +0200, Yitzchak Eidus wrote:
>> is it possible to replace linux kernel internal functions such as
>> schdule () to lets say my_schdule ()  in a run time with a module
>> patch???

Nothing is impossible.

>> (so that every call in the kernel to schdule() will go to my_schdule()... ) 
>> ???
>> 
>> i am talking about a clean/standard way to do such thing

Not clean. Not standard.
And it sounds evil too.

>> (without overwrite the mem address of the function and replace it in a
>> dirty way...)
>
>No.

You would have to patch _every_ callsite. That's too tedious to be 
useful.

(Hey there is SMP alternatives which sounds like it did just that - 
anyone?)



	-`J'
-- 

Re: changing internal kernel system mechanism in runtime by a module patch

[Stephen Hemminger]

On Thu, 16 Nov 2006 21:19:50 +0200
"Yitzchak Eidus" <ieidus@gmail.com> wrote:

> is it possible to replace linux kernel internal functions such as
> schdule () to lets say my_schdule ()  in a run time with a module
> patch???
> (so that every call in the kernel to schdule() will go to my_schdule()... ) ???
> 
> i am talking about a clean/standard way to do such thing
> (without overwrite the mem address of the function and replace it in a
> dirty way...)
> -
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Look at kprobe/jprobe.

-- 
Stephen Hemminger <shemminger@osdl.org>

Re: changing internal kernel system mechanism in runtime by a module patch

[Muli Ben-Yehuda]

On Thu, Nov 16, 2006 at 09:19:50PM +0200, Yitzchak Eidus wrote:

> is it possible to replace linux kernel internal functions such as
> schdule () to lets say my_schdule () in a run time with a module
> patch???  (so that every call in the kernel to schdule() will go to
> my_schdule()... ) ???

Not in Linux.

> i am talking about a clean/standard way to do such thing
> (without overwrite the mem address of the function and replace it in a
> dirty way...)

k42 supports "dynamic hot-swap" and there's been some work done to
bring it into Linux, see e.g.,
http://ozlabs.org/pipermail/k42-discussion/2006-October/001615.html.

Cheers,
Muli

Re: changing internal kernel system mechanism in runtime by a module patch

[Christoph Hellwig]

On Fri, Nov 17, 2006 at 08:47:32AM +0200, Muli Ben-Yehuda wrote:
> > i am talking about a clean/standard way to do such thing
> > (without overwrite the mem address of the function and replace it in a
> > dirty way...)
> 
> k42 supports "dynamic hot-swap" and there's been some work done to
> bring it into Linux, see e.g.,
> http://ozlabs.org/pipermail/k42-discussion/2006-October/001615.html.

This kind of stuff is just sick.  Better let them play with their research
OS for this kind of thing :)  In practice any non-trivial bug fix requires
changes to global data structures so reloading a module doesn't make sense.
And for module-specific problems you should be able to hack around using
kprobes if you really need (but then again for a mission critical system
you should have proper active-active failover clustering anyway)

Re: changing internal kernel system mechanism in runtime by a module patch

[Muli Ben-Yehuda]

On Fri, Nov 17, 2006 at 06:58:29AM +0000, Christoph Hellwig wrote:

> This kind of stuff is just sick.  Better let them play with their research
> OS for this kind of thing :)

sick, research, what's the difference? :-)

> In practice any non-trivial bug fix requires
> changes to global data structures so reloading a module doesn't make
> sense.

... unless you have a mechanism (which k42 does) to interpose between
data structures and the users of said structures, which you can use to
decide when to repace them.

> And for module-specific problems you should be able to hack around using
> kprobes if you really need (but then again for a mission critical system
> you should have proper active-active failover clustering anyway)

I'm not advocating we merge this - nor have I seen the implementation
for Linux yet - no need to preemptively scorch it from orbit :-)

Cheers,
Muli