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    SubjectRe: [PATCH 6/8] ptrace: arch_ptrace -ENOSYS return

    On Thu, 20 Mar 2008, Roland McGrath wrote:
    > The motivation is to get the arch function out of the code path for the
    > machine-independent request handling. I want to be able to change the
    > implementation later without touching the arch code again.

    If there is no stronger motivation than that, then I don't want to have
    this ugly and unnecessary complication.

    I really don't see the advantage of doing

    /* We can't handle it, let the generic code sort it out */
    return -ENOSYS;

    over a

    /* We can't handle it, let the generic code sort it out */
    return ptrace_request(child, request, addr, data);

    in the arch-specific code, and I think the latter version is *much*
    preferable if it avoids this whole unnecessary new abstraction crud and
    odd testing in the generic part.

    > The reason I took the approach I did instead is incrementalism.
    > I can't change that signature without breaking about 22 arch builds.

    Don't worry about the arch builds. If that's your main worry and reason
    for this, it's not worth it. Yes, ptrace changes, and yes, we may have
    arch issues, but no, it's not that big of a deal. Just break them.

    Make sure x86[-64] works, and make sure that other architectures *can*
    work (and explain it on linux-arch) when you have to fix something up, but
    ptrace is a blip on the radar for people, it's not going to be a huge

    > I'm only really prepared to thoroughly verify a change on 2 of those
    > myself.

    .. and you really aren't expected to. It's why we have architecture
    people: if there is a good reason for the change (ie it's not just some
    churn for churns sake), it's largely up to them to make sure the code

    Sure, you need to be able to explain the interface changes and answer
    questions, but as mentioned, the ptrace code is not a big deal: it has
    lots of tiny _details_, but it's not conceptually complex code.

    > So this ugliness seemed like a better bet than waiting for 20 more
    > arch sign-offs before any of it could go in.

    Really, that has never been a major concern. I will _happily_ break the
    odd architectures if I see that it's a matter of changing over some
    detail (ie it's not some fundamentally hard issue for an arch maintaner to
    fix up).

    I think it's *wrong* to add a new an odd calling convention that is less
    readable than what we have now, just to try to avoid something like this
    that really isn't a big problem. It's not like we haven't broken
    architectures over ptrace in the past, and it's also not like it's an area
    that I think anybody has ever lost sleep over..


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