On Wed, Sep 28, 2011 at 11:11 AM, Michael Blizek <michi1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi!
...
On 21:41 Tue 27 Sep , Venkatram Tummala wrote:
> On Tue, Sep 27, 2011 at 9:19 PM, rohan puri <rohan.puri15@xxxxxxxxx> wrote:
> > in device_open() ->You could create something like this:
> >
> > if(var)
> > return -EBUSY
> > var++
> >
> > &
> >
> > in device_release() ->
> >
> > var--
> >
> >
> > I think this should do the job.
> >
> This will prevent other processes to open the file until a process releases
> it. This is not what i need. Only the threads in a process shouldn't be able
> to open the file if it is already opened in the process. Other processes
> should be able to open it.
DEFINE_MUTEX(pidlist_lock);
LIST_HEAD(pidlist);
struct pidlist_node{
struct list_head lh;
pid_t pid;
}
static struct pidlist_node *get_pin(void)
{
struct list_head *curr = pidlist.next;
while (curr != pidlist) {
struct struct pidlist_node *pin = container_of(curr, struct pidlist_node, lh);
if (pin->pid == current->pid) {
Instead of pid check, AFAIK here tgid comparison should be done. Threads in a single process may have different pid but same tgid and we want to restrict access to only one thread in a single process. Right?
return pin;
}
}
return 0;
}
int open(void)
{
struct pidlist_node *pin;
mutex_lock(&pidlist_lock);
pin = get_pin();
if (pin != 0) {
mutex_unlock(&pidlist_lock);
return -EBUSY;
}
pin = kmalloc(sizeof(struct pidlist_node), GFP_KERNEL);
if (pin == 0) {
mutex_unlock(&pidlist_lock);
return -ENOMEM;
}
pin->pid = current->pid;
list_add(&(pin->lh), &pidlist);
mutex_unlock(&pidlist_lock);
}
int close(void)
{
struct pidlist_node *pin;
mutex_lock(&pidlist_lock);
pin = get_pin();
if (pin != 0) {
list_del(&(pin->lh));
kfree(pin);
}
mutex_unlock(&pidlist_lock);
}
-Michi
--
programing a layer 3+4 network protocol for mesh networks
see http://michaelblizek.twilightparadox.com
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