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    SubjectRe: f_ops flag to speed up compatible ioctls in linux kernel
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    On Wed, 2004-09-01 at 03:32, viro@parcelfarce.linux.theplanet.co.uk
    wrote:
    > 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
    >
    > Too bad.
    >
    > > 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.
    > >
    > > Further, adding a command to the ioctl suddenly requires changing
    > > two places - registration code and ioctl itself.
    >
    > So don't add them. Adding a new ioctl is *NOT* a step to be taken lightly -
    > we used to be far too accepting in that area and as somebody who'd waded
    > through the resulting dungpiles over the last months I can tell you that
    > result is utterly revolting.
    >

    By adding a new ioctl you are adding a new use of the BKL. It has been
    suggested on dri-devel that this should be fixed. Is this even
    possible?

    Lee


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