ipcrsc.c

Go to the documentation of this file.

/*
 * Copyright (C) 2006 Ondrej Palkovsky
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/* IPC resources management
 *
 * The goal of this source code is to properly manage IPC resources
 * and allow straight and clean clean-up procedure upon task termination.
 *
 * The pattern of usage of the resources is:
 * - allocate empty phone slot, connect | deallocate slot
 * - disconnect connected phone (some messages might be on the fly)
 * - find phone in slot and send a message using phone
 * - answer message to phone
 * - hangup phone (the caller has hung up)
 * - hangup phone (the answerbox is exiting)
 * 
 * Locking strategy
 *
 * - To use a phone, disconnect a phone etc., the phone must be
 *   first locked and then checked that it is connected
 * - To connect an allocated phone it need not be locked (assigning
 *   pointer is atomic on all platforms)
 *
 * - To find an empty phone slot, the TASK must be locked
 * - To answer a message, the answerbox must be locked
 * - The locking of phone and answerbox is done at the ipc_ level.
 *   It is perfectly correct to pass unconnected phone to these functions
 *   and proper reply will be generated.
 *
 * Locking order
 *
 * - first phone, then answerbox
 *   + Easy locking on calls
 *   - Very hard traversing list of phones when disconnecting because
 *     the phones may disconnect during traversal of list of connected phones.
 *     The only possibility is try_lock with restart of list traversal.
 *
 * Destroying is less frequent, this approach is taken.
 *
 * Phone call
 *
 * *** Connect_me_to ***
 * The caller sends IPC_M_CONNECT_ME_TO to an answerbox. The server
 * receives 'phoneid' of the connecting phone as an ARG3. If it answers
 * with RETVAL=0, the phonecall is accepted, otherwise it is refused.
 *
 * *** Connect_to_me ***
 * The caller sends IPC_M_CONNECT_TO_ME, with special 
 * The server receives an automatically
 * opened phoneid. If it accepts (RETVAL=0), it can use the phoneid
 * immediately. 
 * Possible race condition can arise, when the client receives messages
 * from new connection before getting response for connect_to_me message.
 * Userspace should implement handshake protocol that would control it.
 *
 * Phone hangup
 * 
 * *** The caller hangs up (sys_ipc_hangup) ***
 * - The phone is disconnected (no more messages can be sent over this phone),
 *   all in-progress messages are correctly handled. The anwerbox receives
 *   IPC_M_PHONE_HUNGUP call from the phone that hung up. When all async
 *   calls are answered, the phone is deallocated.
 *
 * *** The answerbox hangs up (ipc_answer(EHANGUP))
 * - The phone is disconnected. EHANGUP response code is sent
 *   to the calling task. All new calls through this phone
 *   get a EHUNGUP error code, the task is expected to
 *   send an sys_ipc_hangup after cleaning up it's internal structures.
 *
 * Call forwarding
 * 
 * The call can be forwarded, so that the answer to call is passed directly
 * to the original sender. However, this poses special problems regarding 
 * routing of hangup messages.
 *
 * sys_ipc_hangup -> IPC_M_PHONE_HUNGUP
 * - this message CANNOT be forwarded
 *
 * EHANGUP during forward
 * - The *forwarding* phone will be closed, EFORWARD is sent to receiver.
 *
 * EHANGUP, ENOENT during forward
 * - EFORWARD is sent to the receiver, ipc_forward returns error code EFORWARD
 *
 * Cleanup strategy
 * 
 * 1) Disconnect all our phones ('ipc_phone_hangup').
 *
 * 2) Disconnect all phones connected to answerbox.
 *
 * 3) Answer all messages in 'calls' and 'dispatched_calls' queues with
 *    appropriate error code (EHANGUP, EFORWARD).
 *
 * 4) Wait for all async answers to arrive and dispose of them.
 * 
 */

#include <synch/spinlock.h>
#include <ipc/ipc.h>
#include <arch.h>
#include <proc/task.h>
#include <ipc/ipcrsc.h>
#include <debug.h>

call_t * get_call(__native callid)
{
        link_t *lst;
        call_t *call, *result = NULL;

        spinlock_lock(&TASK->answerbox.lock);
        for (lst = TASK->answerbox.dispatched_calls.next;
             lst != &TASK->answerbox.dispatched_calls; lst = lst->next) {
                call = list_get_instance(lst, call_t, link);
                if ((__native)call == callid) {
                        result = call;
                        break;
                }
        }
        spinlock_unlock(&TASK->answerbox.lock);
        return result;
}

int phone_alloc(void)
{
        int i;

        spinlock_lock(&TASK->lock);
        
        for (i=0; i < IPC_MAX_PHONES; i++) {
                if (TASK->phones[i].state == IPC_PHONE_HUNGUP && \
                    atomic_get(&TASK->phones[i].active_calls) == 0)
                        TASK->phones[i].state = IPC_PHONE_FREE;

                if (TASK->phones[i].state == IPC_PHONE_FREE) {
                        TASK->phones[i].state = IPC_PHONE_CONNECTING;
                        break;
                }
        }
        spinlock_unlock(&TASK->lock);

        if (i >= IPC_MAX_PHONES)
                return -1;
        return i;
}

static void phone_deallocp(phone_t *phone)
{
        ASSERT(phone->state == IPC_PHONE_CONNECTING);
        
        /* atomic operation */
        phone->state = IPC_PHONE_FREE;
}

void phone_dealloc(int phoneid)
{
        phone_deallocp(&TASK->phones[phoneid]);
}

void phone_connect(int phoneid, answerbox_t *box)
{
        phone_t *phone = &TASK->phones[phoneid];
        
        ASSERT(phone->state == IPC_PHONE_CONNECTING);
        ipc_phone_connect(phone, box);
}

---