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>

diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index b1c11775839cd6543590d98a2d482dd3b9ef769c..9b5915ebeb35ab80d705e6c449390ad5e7775470 100644 (file)
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -1583,7 +1583,7 @@ static int dispatch_ioctl(struct client *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));