source: mainline/kernel/generic/src/ipc/ipcrsc.c@ 01c3bb4

/*
 * 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.
 */

/** @addtogroup genericipc
 * @{
 */
/** @file
 */

/* 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 capability 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 capability 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 ARG5. 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.
 * 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 answerbox 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 its 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 <assert.h>
#include <abi/errno.h>
#include <cap/cap.h>
#include <mm/slab.h>

static bool phone_reclaim(kobject_t *kobj)
{
        bool gc = false;

        mutex_lock(&kobj->phone->lock);
        if (kobj->phone->state == IPC_PHONE_HUNGUP &&
            atomic_get(&kobj->phone->active_calls) == 0)
                gc = true;
        mutex_unlock(&kobj->phone->lock);

        return gc;
}

static void phone_destroy(void *arg)
{
        phone_t *phone = (phone_t *) arg;
        slab_free(phone_slab, phone);
}

static kobject_ops_t phone_kobject_ops = {
        .reclaim = phone_reclaim,
        .destroy = phone_destroy
};


/** Allocate new phone in the specified task.
 *
 * @param task  Task for which to allocate a new phone.
 *
 * @return  New phone capability handle.
 * @return  Negative error code if a new capability cannot be allocated.
 */
cap_handle_t phone_alloc(task_t *task)
{
        cap_handle_t handle = cap_alloc(task);
        if (handle >= 0) {
                phone_t *phone = slab_alloc(phone_slab, FRAME_ATOMIC);
                if (!phone) {
                        cap_free(TASK, handle);
                        return ENOMEM;
                }
                kobject_t *kobject = malloc(sizeof(kobject_t), FRAME_ATOMIC);
                if (!kobject) {
                        cap_free(TASK, handle);
                        slab_free(phone_slab, phone);
                        return ENOMEM;
                }

                ipc_phone_init(phone, task);
                phone->state = IPC_PHONE_CONNECTING;

                kobject_initialize(kobject, KOBJECT_TYPE_PHONE, phone,
                    &phone_kobject_ops);
                phone->kobject = kobject;
                
                cap_publish(task, handle, kobject);
        }
        
        return handle;
}

/** Free slot from a disconnected phone.
 *
 * All already sent messages will be correctly processed.
 *
 * @param handle Phone capability handle of the phone to be freed.
 *
 */
void phone_dealloc(cap_handle_t handle)
{
        kobject_t *kobj = cap_unpublish(TASK, handle, KOBJECT_TYPE_PHONE);
        if (!kobj)
                return;
        
        assert(kobj->phone);
        assert(kobj->phone->state == IPC_PHONE_CONNECTING);
        
        kobject_put(kobj);
        cap_free(TASK, handle);
}

/** Connect phone to a given answerbox.
 *
 * @param handle  Capability handle of the phone to be connected.
 * @param box     Answerbox to which to connect the phone.
 * @return        True if the phone was connected, false otherwise.
 */
bool phone_connect(cap_handle_t handle, answerbox_t *box)
{
        kobject_t *phone_obj = kobject_get(TASK, handle, KOBJECT_TYPE_PHONE);
        if (!phone_obj)
                return false;
        
        assert(phone_obj->phone->state == IPC_PHONE_CONNECTING);
        
        /* Hand over phone_obj reference to the answerbox */
        return ipc_phone_connect(phone_obj->phone, box);
}

/** @}
 */