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    SubjectRe: Request for comments (kdev_t and friends...)
    Oliver Xymoron writes:
    > On Fri, 26 Nov 1999, Richard Gooch wrote:
    >
    > > Oliver Xymoron writes:
    > > > In fact, we should add at least a void *private so that devices can
    > > > be freed of managing their instance data with static arrays indexed
    > > > off minor number.
    > >
    > > With devfs this is really clean. A driver can allocate an instance
    > > structure at probe time, and pass the pointer to devfs_register().
    > > When the device node is opened, file->private_data is initialised with
    > > that pointer. So the driver open() method already has a handle to the
    > > device instance structure, without any lookups being required.
    >
    > That part of the scheme is good, but I'm still not convinced the
    > lookup is a big deal. To open a file, you still end up doing a
    > lookup that matches name to device (ie a dentry hash
    > lookup). There's no reason opening a device couldn't use a similarly
    > fast (or even identical!) method without requiring that the /dev dir
    > be managed inside the kernel. In fact, I think I earlier suggested
    > it's possible to cache the lookup in the inode.

    I'm not saying the extra lookup is going to make all the difference in
    the world. However:

    - one less lookup is always going to be faster

    - devfs is cleaner (which is what matters more to me)

    - why have an extra lookup when there is a simpler, cleaner method?

    Regards,

    Richard....
    Permanent: rgooch@atnf.csiro.au
    Current: rgooch@ras.ucalgary.ca


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