Messages in this thread | | | Subject | Re: f_ops flag to speed up compatible ioctls in linux kernel | From | Lee Revell <> | Date | Wed, 01 Sep 2004 03:47:12 -0400 |
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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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