Re: kldunload kernel: How should the kernel behave when it is requested to unload itself

> On Nov 10, 2023, at 1:03 AM, Warner Losh <imp@bsdimp.com> wrote:
> 
> Yea. Kexec is what you'd need to do to get a new kernel... and we don't support kexec... so I agree this is good..

If we ever want to support kexec, a new kernel should be loaded into memory before the old one is unloaded.
Then probably a dedicated syscall is needed for that.

The current change D42530  is mainly to prevent userland from unloading the kernel via kldunload(2), so it should be OK.

> 
> Warner
> 
> On Thu, Nov 9, 2023, 9:34 AM Doug Rabson <dfr@rabson.org <mailto:dfr@rabson.org>> wrote:
> I think your intuition is correct - it never makes sense to unload the kernel (IMO). I approved the review.
> 
> Doug.
> 
> 
> On Thu, 9 Nov 2023 at 16:10, Zhenlei Huang <zlei@freebsd.org <mailto:zlei@freebsd.org>> wrote:
> Hi,
> 
> This is *NOT* joking.
> 
> While working on https://reviews.freebsd.org/D42527 <https://reviews.freebsd.org/D42527> I realized the
> module kernel also has userrefs, that is to say, userland can request
> to unload kernel, aka `kldunload kernel`.
> 
> This is interesting. Well no doubt that the loader can unload kernel.
> Then after the kernel is loaded and has been initialized (SYSINIT), how
> should it behave when it get an unload request?
> 
> I'm proposing https://reviews.freebsd.org/D42530 <https://reviews.freebsd.org/D42530> to do not allow unloading
> the kernel. It is by intuition.
> 
> What do you think ?
> 
> 
> Best regards,
> Zhenlei
>