Re: Hot swap kernel

Richard Jones (
Wed, 21 Jan 1998 13:07:45 +0000

Kalle Andersson wrote:
> Evening all
> I am sorry if I am the 57th asking for this but it would be great to be able to
> hotswap kernels, ie change kernel without needing to reboot.

A very nice idea, but quite hard to implement. The problem
is that _all_ the data stored by the kernel needs to be
transfered to the new kernel. That is, all the static variables
used everywhere, page tables, process table, file system
mount information and god knows what (possibly outstanding
NFS request information :-), ... Then, of course, the new
kernel has probably changed the semantics of particular
variables or changed the format of particular data
structures, so you need to ``upgrade'' the state to the
new kernel. And, of course, you need different upgrade
modules for different kernel transitions. Imagine the
difficulties of upgrading the state from 1.2.13 -> 2.1.80!
(You can also do it in stages, by chaining together
1.2.13->2.0->2.1 as a _very_ simplified example).

Yuk. Monolithic kernels just don't support this very
well. It might be a lot easier with a microkernel, since
the amount of state you need to deal with is reduced.


Richard Jones Tel: +44 171 460 6141 Fax: .. 4461
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Copyright © 1998 Richard W.M. Jones