locking a device for exclusive use by userspace process (or kernel thread)

[Yann Droneaud]

Hi Greg,

Le mercredi 04 mars 2015 à 10:11 -0800, Greg KH a écrit :
> On Wed, Mar 04, 2015 at 06:59:04PM +0100, Yann Droneaud wrote:
> > Hi,
> > 
> > I have a device and I have to write a driver that exposes the
> > following three operations to kernel modules AND to userspace
> > programs:
> 
> <snip>
> 
> Why?

I'm trying to improve the current driver for this device to allow the 
lock to be released when userspace program owning the lock is killed.

>   What type of device is this?

It's a device with some kind of over complicated mailbox.

A userspace program is supposed to feed the mailbox with multiple 
commands and no other userspace program should be allowed to play with 
the device during that time.

>   And who is asking you to do this homework assignment?
> 

It's not a homework assignment. It's not even something a little penguin
ask me to do.

I was so sure I could map the semaphore sematics to open() and close()
and use that file descriptor to represent the lock that I feel terribly 
sorry for not being able to do so.

(At one point I felt like I was fighting against 40 years of Unix, and
such a fight is not going to be won by myself :)

So I'm back to step 0 and looking for a way to be able to release a 
lock in case of a userspace program is killed.

> good luck,
> 

Thanks :)

Regards.

-- 
Yann Droneaud
OPTEYA