On Wed, 7 Jun 2000, Rogier Wolff wrote:
> James Sutherland wrote:
> > On Wed, 7 Jun 2000, Keith Owens wrote:
> >
> > > On Wed, 7 Jun 2000 10:01:36 +0100 (BST),
> > > James Sutherland <jas88@cam.ac.uk> wrote:
> > > >Then add a
> > > >way to upgrade from one module version to another seamlessly
> > >
> > > It already exists, it is called module symbol versions. If the kernel
> > > and modules were compiled with symbol versions and the versions match
> > > then insmod will load the module, no questions asked. This applies
> > > even if the module and the kernel are for different releases.
> >
> > DOH! s/module/kernel/
> >
> > My aim was that if, say, kernel 2.6.17 and 2.6.18 differ only in the
> > modules, I could upgrade from 2.6.17 to 2.6.18 just by rmmoding the old
> > modules, and insmodding the new ones - no downtime.
> >
> > A useful feature, perhaps, if it can be done...
>
> One of the problem is that to upgrade say the serial driver, you'll
> have to "down" everything using the serial ports, and then "up" them
> again. And how do you go about rmmodding the driver for the harddisk?
> Tricky!
In general, yes, it will be difficult. Having said that, there are quite a
few things I could upgrade quite easily: sound drivers, for example, or
network drivers if I'm connected to the machine via another link (serial,
another NIC, at the console).
> In short, it is usually easier to just kick the whole system down, and
> let it boot from scratch.
>
> Passing the internal state from one version of the module/kernel to
> the next is very, very tricky business.
You don't need to; for an NIC, for example, you could just down it, rmmod,
insmod the new one, and configure it. You are offline for perhaps 10
seconds while the change takes place - which should be OK for most setups.
(With a bit of clever trickery, you could even avoid dropping TCP sessions
etc.)
It will take quite a while to get to this stage, and it won't be perfect,
but it could be quite good...
James.
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