no-op error in dmesg

Hi,
I have one structure called foo. Address of object of foo(say objfoo) is passed to ioctl call

status = ioctl(fd, arg, &objfoo);

But during manipulation I am not getting ioctl error 5 (input/output error). I am more confused about error in dmesg which is
*foo: no-op *

What does no-op indicate? If it is no-operation, how can we relate this to foo structure?

Thanks,
Pritam
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Hi,

as objfoo is a pointer to foo:
struct something foo;
struct somethint *objfoo = &foo;

&objfoo therefore is a pointer to a pointer, not sure if you wanted to pass this to the ioctl.

you can't work directly on a object in userspace memory as this might be a security issue. There exits a function to copy from user memory area to kernel memory area (copy_from_user; and afterwards copy back to the user; copy_to_user).

Cheers,
Matthias