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    SubjectRe: What's left over.
    Jeff Garzik wrote:
    > That said, I used to be an LKCD cheerleader until a couple people made
    > some good points to me: it is not nearly low-level enough to truly be
    > of use in crash situations.

    I'm not so convinced about this. I like the Mission Critical
    approach: save the dump to memory, then either boot through the
    firmware or through bootimg (nowadays, that would be kexec),
    then retrieve the dump from memory, and do whatever you like
    with it.

    The huge advantage here is that you don't need a ton of
    specialized dump drivers and/or have much of the original kernel
    infrastructure to be in a usable state. The rebooted system will
    typically be stable enough to offer the full range of utilities,
    including up to date drivers for all possible devices, so you
    can safely write to disk, scp all the mess to your support
    critter, or post an automatic flame to linux-kernel :-)

    The weak points of the Mission Critical design are that early
    memory allocation in the kernel needs to be tightly controlled,
    that architectures that wipe CPU caches on reboot need to
    commit them to memory before the firmware restart, and that
    drivers need to be able to recover from an "unclean" hardware
    state. (I think we'll see much of the latter happen as kexec
    advances. The other two issues aren't really special.)

    Actually, at the RAS BOF I thought that IBM were developing LKCD
    in this direction, and had also eliminated a few not so elegant
    choices of Mission Critical's original design. I haven't looked
    at the LKCD code, but the descriptions sound as if all the
    special-case cruft seems to be back again, which I would find a
    little disappointing.

    There might be a case for specialized low-overhead dump handlers
    for small embedded systems and such, but they're probably better
    maintained outside of the mainstream kernel. (They're more like
    firmware anyway.)

    - Werner

    --
    _________________________________________________________________________
    / Werner Almesberger, Buenos Aires, Argentina wa@almesberger.net /
    /_http://www.almesberger.net/____________________________________________/
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