Re: Hot swap kernel

docwhat@gerf.org ;The Doctor What ("docwhat@gerf.org)
Wed, 21 Jan 1998 15:29:08 -0800

Repeating what you said:
->Many portables has got a feature which allows you to turn of the
machine and
->restart it without needing to boot again. Basically I think it flushes the
->memory and info about processes.. Before it does that it probably
syncs the
->discs etc. This feature didn't work to well on Linux but the theory...
->I am not sure (as usual) but if it would be possible to freeze the system,
->flush all interesting info including the entire memory and make the
new kernel
->cooperate with the "old" info..
->Perhaps it would only operate if we killed all processes perhaps even
umounting
->all filesystems. This wouldn't be bad at all. I can imagine this
won't take
->more then perhaps 10 seconds. A major time saving compared to a complete
->reboot... But then all network connections would be lost, but it is
at least a
->start =)

I believe that the feature in laptops that you mention doesn't connect
with the OS. Specifically, I believe that the hardware in the laptop
saves the state of the Memory, CPU and Video, then simply turns off the
power. When it re-starts, it loads everything back in place and tells
the cpu to "go".

Am I wrong? I had a friend who installed an ancient copy of Win3.0 on
one of these Laptops (it was originally a Win95 OEM2 laptop) and it
worked fine. Ditto DOS version 3 thru 6 and OS/2.

If Linux was persistant (i.e. it saved memory, process*, and filesystem
states between "shutdowns") then rebooting to install the next version
of the OS would be fine, since it'd just reload the old memory,
process, etc. Then you'd have no problem with temporarily shutting
down the core kernel and loading up a new one without an actual "reboot".

* Yeah, I know...not all definitions of persistance include processes.

Ciao!
-=Doc

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