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1072 palkovsky 1 
/*
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 * Copyright (C) 2006 Ondrej Palkovsky
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 * All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 *
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 * - Redistributions of source code must retain the above copyright
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 *   notice, this list of conditions and the following disclaimer.
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 * - Redistributions in binary form must reproduce the above copyright
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 *   notice, this list of conditions and the following disclaimer in the
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 *   documentation and/or other materials provided with the distribution.
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 * - The name of the author may not be used to endorse or promote products
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 *   derived from this software without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
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/* IPC resources management
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 *
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 * The goal of this source code is to properly manage IPC resources
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 * and allow straight and clean clean-up procedure upon task termination.
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 *
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 * The pattern of usage of the resources is:
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 * - allocate empty phone slot, connect | deallocate slot
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 * - disconnect connected phone (some messages might be on the fly)
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 * - find phone in slot and send a message using phone
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 * - answer message to phone
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 *
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 * Locking strategy
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 *
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 * - To use a phone, disconnect a phone etc., the phone must be
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 *   first locked and then checked that it is connected
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 * - To connect an allocated phone it need not be locked (assigning
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 *   pointer is atomic on all platforms)
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 *
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 * - To find an empty phone slot, the TASK must be locked
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 * - To answer a message, the answerbox must be locked
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 * - The locking of phone and answerbox is done at the ipc_ level.
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 *   It is perfectly correct to pass unconnected phone to these functions
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 *   and proper reply will be generated.
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 *
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 * - There may be objection that a race may occur when the syscall finds
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 *   an appropriate call and before executing ipc_send, the phone call might
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 *   be disconnected and connected elsewhere. As there is no easy solution,
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 *   the application will be notified by an  'PHONE_DISCONNECTED' message
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 *   and the phone will not be allocated before the application notifies
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 *   the kernel subsystem that it does not have any pending calls regarding
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 *   this phone call.
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 *
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 * Locking order
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 *
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 * There are 2 possibilities
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 * - first phone, then answerbox
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 *   + Easy locking on calls
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 *   - Very hard traversing list of phones when disconnecting because
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 *     the phones may disconnect during traversal of list of connected phones.
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 *     The only possibility is try_lock with restart of list traversal.
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 *
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 * - first answerbox, then phone(s)
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 *   + Easy phone disconnect
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 *   - Multiple checks needed when sending message
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 *
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 * Because the answerbox destroyal is much less frequent operation,
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 * the first method is chosen.
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 *
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 * Cleanup strategy
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 *
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 * 1) Disconnect all phones.
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 *    * Send message 'PHONE_DISCONNECTED' to the target application
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 * - Once all phones are disconnected, no further calls can arrive
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 *
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 * 2) Answer all messages in 'calls' and 'dispatched_calls' queues with
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 *    appropriate error code.
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 *
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 * 3) Wait for all async answers to arrive
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 * Alternatively - we might try to invalidate all messages by setting some
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 * flag, that would dispose of the message once it is answered. This
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 * would need to link all calls in one big list, which we don't currently
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 * do.
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 *
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 *
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 */
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#include <synch/spinlock.h>
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#include <ipc/ipc.h>
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#include <arch.h>
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#include <proc/task.h>
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#include <ipc/ipcrsc.h>
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#include <debug.h>
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/** Find call_t * in call table according to callid
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 *
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 * @return NULL on not found, otherwise pointer to call structure
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 */
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call_t * get_call(__native callid)
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{
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    /* TODO: Traverse list of dispatched calls and find one */
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    /* TODO: locking of call, ripping it from dispatched calls etc.  */
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    return (call_t *) callid;
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}
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/** Allocate new phone slot in current TASK structure */
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int phone_alloc(void)
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{
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    int i;
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    spinlock_lock(&TASK->lock);
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    for (i=0; i < IPC_MAX_PHONES; i++) {
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        if (!TASK->phones[i].busy) {
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            TASK->phones[i].busy = 1;
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            break;
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        }
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    }
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    spinlock_unlock(&TASK->lock);
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    if (i >= IPC_MAX_PHONES)
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        return -1;
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    return i;
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}
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/** Disconnect phone */
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void phone_dealloc(int phoneid)
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{
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    spinlock_lock(&TASK->lock);
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    ASSERT(TASK->phones[phoneid].busy);
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    if (TASK->phones[phoneid].callee)
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        ipc_phone_destroy(&TASK->phones[phoneid]);
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    TASK->phones[phoneid].busy = 0;
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    spinlock_unlock(&TASK->lock);
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}
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/** Connect phone to a given answerbox
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 *
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 * @param phoneid The slot that will be connected
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 *
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 * The procedure _enforces_ that the user first marks the phone
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 * busy (e.g. via phone_alloc) and then connects the phone, otherwise
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 * race condition may appear.
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 */
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void phone_connect(int phoneid, answerbox_t *box)
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{
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    phone_t *phone = &TASK->phones[phoneid];
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    ASSERT(phone->busy);
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    ipc_phone_connect(phone, box);
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}