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    SubjectRe: [discuss] f_ops flag to speed up compatible ioctls in linux kernel
    On Wed, Sep 01, 2004 at 10:22:45AM +0300, Michael S. Tsirkin wrote:
    > Hello!
    > Currently, on the x86_64 architecture, its quite tricky to make
    > a char device ioctl work for an x86 executables.
    > In particular,
    > 1. there is a requirement that ioctl number is unique -
    > which is hard to guarantee especially for out of kernel modules

    Yes, that is a problem for some people. But you should
    have used an unique number in the first place.

    There are some hackish ways to work around it for non modules[1], but at some
    point we should probably support it better.

    [1] it can be handled, except for module unloading, so you have
    to disable that.

    > 2. there's a performance huge overhead for each compat call - there's
    > a hash lookup in a global hash inside a lock_kernel -
    > and I think compat performance *is* important.

    Did you actually measure it? I doubt it is a big issue.

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