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    SubjectRe: systemtap & backward compatibility, was Re: [RFC] systemtap: begin the process of using proper kernel APIs
    Arjan van de Ven <> writes:

    > [...]
    >> It does happen to *generate* kernel modules. The way that such a
    >> module must interface with any particular kernel is naturally subject
    >> to the whims & desires of the kernel du jour. This is why we have a
    >> mass of mechanism to try to automatically speak to each kernel version
    >> as appropriate.

    > and this is where I strongly disagree. THIS part *has* to be in the
    > kernel source, so that we can change it WITH the kernel as we change
    > it. [...] But to have any chance at all of systemtap being
    > sustainable, this part of the stack has to be together with where
    > the changes happen.

    OK. It will take us some time to figure out to what extent this would
    be feasible. Maybe a topic for Portland.

    >> It is desirable to minimize this mass for obvious reasons. When a new
    >> upstream kernel comes out with a tasty new feature -- or a less tasty
    >> API rewrite -- we need to extend systemtap to support that too.
    > At that point you are already 3 months too late for me, and probably
    > for most of my fellow kernel hackers.

    (Really? Have we ever been 3 months behind supporting the git kernel?)

    > (and when it's seen it gets a rather luke warm reception, but that's
    > a different story).

    I hope the backward compatibility issue, as it stands today, helps
    explain the reasons for the current deal with kprobes.

    In the interim (before we come up with a way of moving more
    kernel-coupled systemtap code into, would y'all
    consider an arrangement? Those of you who care about systemtap, and
    are intending to make an incompatible kernel/module interface change,
    please run the systemtap testsuite before & after. If it regresses,
    send us a note or a patch. If practical, we'll integrate it (and add
    any backward-compatibility hacks if needed) into systemtap.

    - FChE

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