----- Original Message -----
From: "Helge Hafting" <firstname.lastname@example.org>
To: "C. Slater" <email@example.com>
Sent: Wednesday, July 11, 2001 5:10 AM
Subject: Re: Switching Kernels without Rebooting?
> "C. Slater" wrote:
> > I don't think that it would be possible to switch kernels when one was
> > properly set up to do it, if thats what you mean. You could only switch
> > between kernels that have been compiled to support live switching.
> > I do see you'r point with the datastructures changeing. We would need to
> > some format that all properly setup kernels could understand,
> That seems completely out of question. The structures a 2.4.7
> kernel understands might be insufficient to express the setup
> a future 2.6.9 kernel is using to do its stuff better. (And vice
> versa, if future kernels drop a 2.4.7 feature deemed obsolete.
> But what if that feature is in use when you decide to upgrade?)
> You can easily deal with simple stuff like struct
> rearrangement and type conversions, but what to do when whole data
> change completely?
> Example: something changes from two linked lists representation to a
> single tree or 4 hashtables. You'll have a very hard time inventing
> a generic data format to deal with that kind of changes. It might
> happen. Look at differences in 2.2 and 2.4 VM with the big pagecache
> change in early 2.3. And the dentry cache that suddenly appeared.
> And of course the rules change too, from time to time.
> Many releases have a list of "active pages". what kind exactly is that?
> The rules may change, what to do if the new kernel don't allow
> one particular kind of page on that list, but the old running kernel
> have a bunch?
> This was jsut some made-up examples, I guess you'll run into a ton
> of such issues. New releases aren't simply fixes and tweaks, there
> are frequent design changes.
> > Are you saying that swaping the kernels out altogether would be a
> > task, or that saveing/restoring the datastructures would be a massive
> All you need to swap kernel images is memory. Swapping structures
> can't be done in a generic way, you'll need code that convert the
> structures of one particular kernel release to those of a
> particular other kernel. And I don't think you'll have the usual
> kernel developers do that.
> A "long-term uptime" distro might do this kind of work for a few
> selected kernels, but I cannot imagine it happen for the regular
> Helge Hafting
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