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    SubjectRe: [PATCH 14/16] IB uverbs: add mthca user CQ support
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        >> + int is_kernel;

    Andrew> I assume we have one body of code which is capable of
    Andrew> handling data structures in either kenrel memory of user
    Andrew> memory? (guess).

    Andrew> If so, that's a fairly sensitive thing to be doing. Tell
    Andrew> us more, please.

    It's actually not that bad. A completion queue (CQ) is a basically a
    chunk of memory where completion information is written when a work
    request completes. The hardware can handle many CQs (64K is not an
    unreasonable number), and we always do things like allocation of CQ
    numbers, programming HW for CQ context, etc. in the kernel.

    Both the kernel and userspace can do data path operations like looking
    for a new CQ entry. This means that for userspace CQs, the actual
    memory where entries are written should be in userspace. However the
    struct mthca_cq will always be in the kernel.

    If you look at how the is_kernel flag is used, you can see that all it
    does is control whether we allocate/free the actual buffer and a few
    other things in the kernel, or just use the stuff that userspace has
    already allocated.

    - R.
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