msgsnd in module

msgsnd in module

[Vijayalakshmi Hadimani]

Hi,
   I am inserting a module(device driver) using insmod. 
I want to send a message from this module to an user process.
For this I used msgsnd with buffer in the call as a local 
variable.  I am getting an error "EFAULT" for this call. 
However this did not happen when I made the driver code as a
part of kernel and not as a module.  Any idea about what could
be the problem and how to solve it?

TIA

Regards,
Vijayalakshmi

Re: msgsnd in module

[Robert Hancock]

Vijayalakshmi Hadimani wrote:
> Hi,
>    I am inserting a module(device driver) using insmod. 
> I want to send a message from this module to an user process.
> For this I used msgsnd with buffer in the call as a local 
> variable.  I am getting an error "EFAULT" for this call. 
> However this did not happen when I made the driver code as a
> part of kernel and not as a module.  Any idea about what could
> be the problem and how to solve it?

Well, first off, sending SysV messages from the kernel is a pretty 
bizarre thing to do. Secondly, you can't just call the system call from 
inside the kernel and pass in kernel memory, because the system call 
expects to deal with user-space memory. You'd have to duplicate some or 
all of the code of msgsnd and change it to just read the memory directly 
  instead of using copy_from_user, etc.