no-op error in dmesg

Matthias Brugger matthias.bgg at
Tue Jun 19 05:41:39 EDT 2012


On 06/18/2012 08:34 PM, Pritam Bankar wrote:
> Hi,
> I have one structure called foo. Address of object of foo(say objfoo) is
> passed to ioctl call
> status = ioctl(fd, arg, &objfoo);

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.

> 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 *

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).


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