/* Returns nonzero if this process's lock is released, and 0 if this process
did not hold a lock. */
static int try_release_lock(osprd_info_t *d, struct file *filp, int filp_writable)
{
if (d->write_lock_pid == current->pid)
{
if (!filp_writable)
eprintk("How did I acquire this write lock??");
d->write_lock_pid = -1;
filp->f_flags &= ~F_OSPRD_LOCKED;
}
else if (int_list_contains(d->read_lock_list, current->pid))
{
int_list_remove(d->read_lock_list, current->pid);
if (int_list_empty(d->read_lock_list)) /* Set to unlocked if no other read locks */
filp->f_flags &= ~F_OSPRD_LOCKED;
}
else /* No locks held by this process */
{
return 0;
}
return 1;
}
/*
* osprd_ioctl(inode, filp, cmd, arg)
* Called to perform an ioctl on the named file.
*/
int osprd_ioctl(struct inode *inode, struct file *filp,
unsigned int cmd, unsigned long arg)
{
osprd_info_t *d = file2osprd(filp); // device info
int r = 0; // return value: initially 0
// is file open for writing?
int filp_writable = (filp->f_mode & FMODE_WRITE) != 0;
// Set 'r' to the ioctl's return value: 0 on success, negative on error
if (cmd == OSPRDIOCACQUIRE) {
// EXERCISE: Lock the ramdisk.
//
// If *filp is open for writing (filp_writable), then attempt
// to write-lock the ramdisk; otherwise attempt to read-lock
// the ramdisk.
//
// This lock request must block using 'd->blockq' until:
// 1) no other process holds a write lock;
// 2) either the request is for a read lock, or no other process
// holds a read lock; and
// 3) lock requests should be serviced in order, so no process
// that blocked earlier is still blocked waiting for the
// lock.
//
// If a process acquires a lock, mark this fact by setting
// 'filp->f_flags |= F_OSPRD_LOCKED'. You also need to
// keep track of how many read and write locks are held:
// change the 'osprd_info_t' structure to do this.
//
// Also wake up processes waiting on 'd->blockq' as needed.
//
// If the lock request would cause a deadlock, return -EDEADLK.
// If the lock request blocks and is awoken by a signal, then
// return -ERESTARTSYS.
// Otherwise, if we can grant the lock request, return 0.
// 'd->ticket_head' and 'd->ticket_tail' should help you
// service lock requests in order. These implement a ticket
// order: 'ticket_tail' is the next ticket, and 'ticket_head'
// is the ticket currently being served. You should set a local
// variable to 'd->ticket_head' and increment 'd->ticket_head'.
// Then, block at least until 'd->ticket_tail == local_ticket'.
// (Some of these operations are in a critical section and must
// be protected by a spinlock; which ones?)
unsigned my_ticket;
int ret;
osp_spin_lock(&d->mutex);
/* Check for deadlock: can't acquire r/w lock if already locked by this process */
if (int_list_contains(d->read_lock_list, current->pid) ||
d->write_lock_pid == current->pid)
{
osp_spin_unlock(&d->mutex);
return -EDEADLK;
}
/* Increment ticket_head after checking for deadlock, or else ticket becomes invalid */
my_ticket = d->ticket_head++;
/* If write lock request, must wait until no more read locks AND no more write locks;
if read lock request, wait until no more write locks. */
if (filp_writable)
{
osp_spin_unlock(&d->mutex);
ret = wait_event_interruptible(d->blockq, d->ticket_tail == my_ticket &&
int_list_empty(d->read_lock_list) &&
d->write_lock_pid == -1);
if (!ret)
{
/* Set device to locked, indicate that this process holds the write lock,
and advance d->ticket_tail. */
osp_spin_lock(&d->mutex);
filp->f_flags |= F_OSPRD_LOCKED;
d->write_lock_pid = current->pid;
advance_to_next_valid_ticket(d);
osp_spin_unlock(&d->mutex);
}
else /* Woken up by signal */
{
/* If ticket_tail == this thread's ticket, advance to next valid ticket;
otherwise, mark this thread's ticket as invalid */
SIGNAL_WAKE_UP:
if (d->ticket_tail == my_ticket)
{
osp_spin_lock(&d->mutex);
advance_to_next_valid_ticket(d);
osp_spin_unlock(&d->mutex);
}
else
{
osp_spin_lock(&d->mutex);
int_list_add(d->invalid_tickets, my_ticket);
osp_spin_unlock(&d->mutex);
}
return -ERESTARTSYS;
}
}
else
{
osp_spin_unlock(&d->mutex);
ret = wait_event_interruptible(d->blockq, d->ticket_tail == my_ticket &&
d->write_lock_pid == -1);
if (!ret)
{
/* Set device to locked, indicate that this process holds a read lock,
and advance d->ticket_tail. */
osp_spin_lock(&d->mutex);
filp->f_flags |= F_OSPRD_LOCKED;
int_list_add(d->read_lock_list, current->pid);
advance_to_next_valid_ticket(d);
osp_spin_unlock(&d->mutex);
wake_up_all(&d->blockq);
}
else /* Woken up by signal */
goto SIGNAL_WAKE_UP;
}
r = 0;
} else if (cmd == OSPRDIOCTRYACQUIRE) {
// EXERCISE: ATTEMPT to lock the ramdisk.
//
// This is just like OSPRDIOCACQUIRE, except it should never
// block. If OSPRDIOCACQUIRE would block or return deadlock,
// OSPRDIOCTRYACQUIRE should return -EBUSY.
// Otherwise, if we can grant the lock request, return 0.
osp_spin_lock(&d->mutex);
/* Check for deadlock normally */
if (int_list_contains(d->read_lock_list, current->pid) ||
d->write_lock_pid == current->pid)
{
osp_spin_unlock(&d->mutex);
return -EBUSY;
}
/* Check for lock acquire conditions:
- ticket_tail must equal ticket_head
- there must be no write lock
- if write lock request, must be no read locks */
if (d->ticket_head != d->ticket_tail || d->write_lock_pid != -1)
{
osp_spin_unlock(&d->mutex);
return -EBUSY;
}
if (filp_writable && !int_list_empty(d->read_lock_list))
{
osp_spin_unlock(&d->mutex);
return -EBUSY;
}
/* Acquire the read/write lock */
if (filp_writable)
d->write_lock_pid = current->pid;
else
int_list_add(d->read_lock_list, current->pid);
filp->f_flags |= F_OSPRD_LOCKED;
osp_spin_unlock(&d->mutex);
wake_up_all(&d->blockq);
r = 0;
} else if (cmd == OSPRDIOCRELEASE) {
// EXERCISE: Unlock the ramdisk.
//
// If the file hasn't locked the ramdisk, return -EINVAL.
// Otherwise, clear the lock from filp->f_flags, wake up
// the wait queue, perform any additional accounting steps
// you need, and return 0.
/* Same as release procedure in osprd_close_last() */
osp_spin_lock(&d->mutex);
if (try_release_lock(d, filp, filp_writable))
{
osp_spin_unlock(&d->mutex);
wake_up_all(&d->blockq);
}
else
{
osp_spin_unlock(&d->mutex);
}
r = 0;
} else
r = -ENOTTY; /* unknown command */
return r;
}
char *test_empty(){
IntList *il = create_int_list();
mu_assert(int_list_empty(il), "La lista de enteros esta vacia");
return NULL;
}
