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    Subject[PATCH] firewire: cdev: return -ENOTTY for unimplemented ioctls, not -EINVAL
    On Jun 27 Linus Torvalds wrote:
    > The correct error code for "I don't understand this ioctl" is ENOTTY.
    > The naming may be odd, but you should think of that error value as a
    > "unrecognized ioctl number, you're feeding me random numbers that I
    > don't understand and I assume for historical reasons that you tried to
    > do some tty operation on me".
    [...]
    > The EINVAL thing goes way back, and is a disaster. It predates Linux
    > itself, as far as I can tell. You'll find lots of man-pages that have
    > this line in it:
    >
    > EINVAL Request or argp is not valid.
    >
    > and it shows up in POSIX etc. And sadly, it generally shows up
    > _before_ the line that says
    >
    > ENOTTY The specified request does not apply to the kind of object
    > that the descriptor d references.
    >
    > so a lot of people get to the EINVAL, and never even notice the ENOTTY.
    [...]
    > At least glibc (and hopefully other C libraries) use a _string_ that
    > makes much more sense: strerror(ENOTTY) is "Inappropriate ioctl for
    > device"

    So let's correct this in the <linux/firewire-cdev.h> ABI while it is
    still young, relative to distributor adoption.

    Side note: We return -ENOTTY not only on _IOC_TYPE or _IOC_NR mismatch,
    but also on _IOC_SIZE mismatch. An ioctl with an unsupported size of
    argument structure can be seen as an unsupported version of that ioctl.

    Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
    Cc: <stable@kernel.org>
    ---
    drivers/firewire/core-cdev.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    Index: b/drivers/firewire/core-cdev.c
    ===================================================================
    --- a/drivers/firewire/core-cdev.c
    +++ b/drivers/firewire/core-cdev.c
    @@ -1583,7 +1583,7 @@ static int dispatch_ioctl(struct client
    if (_IOC_TYPE(cmd) != '#' ||
    _IOC_NR(cmd) >= ARRAY_SIZE(ioctl_handlers) ||
    _IOC_SIZE(cmd) > sizeof(buffer))
    - return -EINVAL;
    + return -ENOTTY;

    if (_IOC_DIR(cmd) == _IOC_READ)
    memset(&buffer, 0, _IOC_SIZE(cmd));

    --
    Stefan Richter
    -=====-==-== -=== -=--=
    http://arcgraph.de/sr/

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