[gentoo-amd64] Re: Gentoo crashing?

[Duncan]

"Boyd Stephen Smith Jr." <bss03@××××××××××.net> posted
200705190231.33752.bss03@××××××××××.net, excerpted below, on  Sat, 19 May
2007 02:31:27 -0500:

> On Friday 18 May 2007 23:45:42 Peter Davoust wrote:
>> Actually, I wanted to ask a some what unrelated question as well: I've
>> heard it's possible to update kernel without rebooting, and while I'm
>> not sure of the advisability, I'm getting things to work here and I'd
>> like to not have to reboot my computer so many times. Besides, it just
>> sounds cool. Could someone tell me how to do it?
>
> I've done it before via kexec, but I don't remember exactly how.  Google
> for: linux kexec how-to
> and you should get some useful links.

I'm going to go out on a limb here (but not so far, I think), and say 
most folks shouldn't be worried about kexec at this point.  There are a 
lot of unpredictables in terms of hardware state once the new kernel is 
started, many of which the kernel isn't yet expecting (it expects to 
start with everything in a known or just initialized state) or prepared 
to deal with, and most folks won't be prepared to deal with the potential 
crashes and even possible data loss, if things don't go quite right.

kexec is coming along (just with kernel 2.6.22-rc1 a critical piece was 
placed for x86_64/amd64 users, an x86_64 kernel can now be compiled as 
relocatable, according to the changelog), but I don't believe any 
involved kernel hacker would tell you it's ready for ordinary prime-time 
use, yet.  I'd say another six months to a year, anyway, maybe more if 
development focuses on other areas more and less on kexec.

Without kexec, in general, no, one has to reboot to make use of a new 
kernel or its features.  However, it IS possible to build modules and 
insert them into a running kernel.  Of course, that works best if it's 
modules for the same kernel and using the same CFLAGS. I'm sufficiently 
cautious not to even consider otherwise, but it does sometimes work (and 
in fact, with proprietary closed source modules, /must/ work, to /some/ 
extent, but I don't run those, either).  So yes, even without kexec, if 
all you are doing is building additional modules, particularly if it's 
the same kernel sources and cflags, you should be able to load those 
modules in the running kernel without damage or indeed undue risk.  The 
kernel is in fact designed for such module loading.  (The big risk is in 
unloading modules, particularly in /force/ unloading, because it can 
create serious race and unknown state conditions.  There's still an 
option for forced unload, however, with the caveat that it's discouraged, 
and only for use where the alternative would be reboot anyway, and the 
risk of kernel instability is considered less of a loss than the reboot 
might be.)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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