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    SubjectRe: ioctl cleanups: enable sg_io and serial stuff to be shared
    On Wednesday 07 May 2003 18:04, David S. Miller wrote:
    > You can define it as follows:
    > 1) If entry exists in COMPAT or TRANSLATE table, invoke
    > fops->ioctl(), else
    > 2) If ->compat_ioctl() exists, invoke that, else
    > 3) Fail.

    Another solution could be to use the tables only if
    ->compat_ioctl() is undefined or returned -ENOTTY. That
    would save the hash table lookup in many cases and makes
    it possible for a driver to override a generic handler
    with its more specialized version (e.g. CIODEVPRIVATE).

    > The COMPAT tables are sort of valuable, in that it eliminates
    > the need to duplicate code when all of a drivers ioctls need
    > no translation.

    Right. Of course you can just as well do

    .ioctl = &foo_ioctl,
    .compat_ioctl = &foo_ioctl,

    in that case.

    Btw: is there any bit in the ioctl number definition that can
    be (ab)used for compat_ioctl? Maybe we don't even need another
    callback if the compatibility mode can be encoded in the
    number itself (simplified):

    long compat_sys_ioctl(unsigned int fd, unsigned int cmd,
    unsigned long arg)
    long err = sys_ioctl(fd, cmd | _IOC_COMPAT, arg);
    if (err == -ENOTTY) /* use ioctl_trans table */
    err = compat_do_ioctl(fd, cmd, arg);
    return err;
    long foo_ioctl(struct inode * inode, struct file * filp,
    unsigned int cmd, unsigned long arg)
    switch(cmd) {
    case SOMEIOCTL:
    return do_something(inode, arg);
    return compat_do_something(inode, arg);
    return do_something_else(inode, arg);
    return -ENOTTY;

    Arnd <><
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