Re: hot patching

[Pratap Chakravarthy <pratap.chakravarthy@xxxxxxxxx>]

Thanks a lot.
    U have painted exactly what i am thinking of. I agree the points. But the line

>>    * Whenever possible, compile your code as a kernel module. You can load/unload
 >> your code without rebooting.
    confuses me. I havnt understood the micro kernel architechture in full. How far the kernel
    part can be modularised ?!!! any way i will have a study on that.

Once again thanks.
pratap

Raja Subramanian wrote:

> Pratap Chakravarthy wrote (pratap.chakravarthy@xxxxxxxxx):
>
> > Can you please tell me the feasibility of hot patching in an operating
> > system like linux and if possible please provide me with any details or
> > pointers on that.  I saw in the sun's web site that they have provided
> > hot patching in their solaris 8. How far it is reliable.
>
> Reliability of hot patching is questionable. I've seen solaris "panic" after a
> hotpatch. I would not hotfix a busy running system, planned downtime sounds
> safer. But that does not mean that hot patching is a bad idea anyway.
>
> > what is hot patching ?
> >  It is nothing but replacing a function present in the memory "on fly".In
> >  usual cases suppose there is  a  bug in the kernel code, that bug has to be
> >  removed and then compiled and linked to get the image [kernel image],which
> >  is then booted. Here in hot patching the debuged function has to be
> >  compiled. Then it is linked with the kernel without rebooting the system,
> >  on the fly.
>
> > I dont know whether this facility is really required for linux. But for any
> > OS developer, this tool is a required one.
>
> Possible solutions for an OS developer who does not want to reboot -
>
> * Whenever possible, compile your code as a kernel module. You can load/unload
>   your code without rebooting.
> * Run/debug the kernel you're developing in user mode. See "use mode linux".
> * Rewrite the linux kernel in erlang (just kidding...)
>
> The closest linux ever came to restarting without rebooting (in the
> Ctrl+Alt+Del sense) was with the "two kernel monte". This invloves restarting
> with a new kernel without rebooting the machine.
> Note: You will kill all processes as a result, so this is probably not what
> you want.
>
> Due to its modular design, hotpatching is easier with micro-kernel
> implementations like the Hurd. Even then, there may be seveal bugs which
> cannot be hotpatched.
>
> - Raja
>
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