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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 <>
Cc: <>
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
-=====-==-== -=== -=--=

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