Re: Locking IOCTL

[Praveen kumar <chatpravi@xxxxxxxxx>]

The driver is opened by multiple processes, One such process is a diagnostics.
Where I am checking sanity of some of the registers if I make ioctl open for all the processes.It can screw 
up my diagnostics check.(write some values to registers). This is basic reason I am using lock to my ioctl.

Thanks 
Praveen

On Tue, Nov 15, 2011 at 1:28 PM, Dave Hylands <dhylands@xxxxxxxxx> wrote:

Hi Praveen,

On Mon, Nov 14, 2011 at 11:22 PM, Praveen kumar <chatpravi@xxxxxxxxx> wrote:
>
> Hi All,
> I have a situation where I have to lock the ioctl provided in my driver. I
> have a uni processor (ARM) system.
> I am using Mutex as the lock for my ioctl.
> DEFINE_MUTEX(&lock_ioctl);
> MyIoctl()
> {
> Mutex_lock(&lock_ioctl);
> Switch(){
> ...........
> }
> Mutex_unlock(&lock_ioctl);
> return 0;
> }
> I just wanted to know am I using the best lock available for the situation
> aor do I have any flaw in my implementation???
>
> And from LKD I  read that "*lock the data not the code*" and which I am
> literally doing so ?? any comments on this ?

By creatiing something called lock_ioctl, I'd say you're locking the code.

Locking the data means that lets suppose you have some data structure
which requires mutual exclusion. Then I'd create a lock associated
with that data structure (and probably the lock would be a member of
the data structure), and anytime I needed to manipulate/access the
data structure (in an atomic manner), I'd acquire the lock.

> I have interrupts in my driver which is nothing to do with the lock.I am
> taking care that where ever I return in my ioctl the lock is released.

What are you locking? Does every single ioctl really need to acquire
the lock? Why?

--
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com

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