WebSVN – HelenOS-historic – Diff – /kernel/trunk/generic/src/ipc/ipcrsc.c

 /*
  * 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
+ *
+ * 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.
+ *
+ * - There may be objection that a race may occur when the syscall finds
+ *   an appropriate call and before executing ipc_send, the phone call might
+ *   be disconnected and connected elsewhere. As there is no easy solution,
+ *   the application will be notified by an  'PHONE_DISCONNECTED' message
+ *   and the phone will not be allocated before the application notifies
+ *   the kernel subsystem that it does not have any pending calls regarding
+ *   this phone call.
+ *
+ * Locking order
+ *
+ * There are 2 possibilities
+ * - 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.
+ *
+ * - first answerbox, then phone(s)
+ *   + Easy phone disconnect
+ *   - Multiple checks needed when sending message
+ *
+ * Because the answerbox destroyal is much less frequent operation,
+ * the first method is chosen.
+ *
+ * Cleanup strategy
+ *
+ * 1) Disconnect all phones.
+ *    * Send message 'PHONE_DISCONNECTED' to the target application
+ * - Once all phones are disconnected, no further calls can arrive
+ *
+ * 2) Answer all messages in 'calls' and 'dispatched_calls' queues with
+ *    appropriate error code.
+ *
+ * 3) Wait for all async answers to arrive
+ * Alternatively - we might try to invalidate all messages by setting some
+ * flag, that would dispose of the message once it is answered. This
+ * would need to link all calls in one big list, which we don't currently
+ * do.
+ *
+ *
  */
 #include <synch/spinlock.h>
 #include <ipc/ipc.h>
 #include <arch.h>
 #include <proc/task.h>
 #include <ipc/ipcrsc.h>
 #include <debug.h>
 /** Find call_t * in call table according to callid
+ *
  * @return NULL on not found, otherwise pointer to call structure
  */
 call_t * get_call(__native callid)
+{
     /* TODO: Traverse list of dispatched calls and find one */
     /* TODO: locking of call, ripping it from dispatched calls etc.  */
     return (call_t *) callid;
+}
-/** Return pointer to phone identified by phoneid or NULL if non-existent */
-phone_t * get_phone_and_lock(__native phoneid)
-{
-    phone_t *phone;
-    if (phoneid >= IPC_MAX_PHONES)
-        return NULL;
-    phone = &TASK->phones[phoneid];
-    spinlock_lock(&phone->lock);
-    if (!phone->callee) {
-        spinlock_unlock(&phone->lock);
-        return NULL;
-    }
-    /* TODO... */
-    spinlock_unlock(&phone->lock);
-    return phone;
-}
 /** Allocate new phone slot in current TASK structure */
 int phone_alloc(void)
+{
     int i;
     spinlock_lock(&TASK->lock);
     for (i=0; i < IPC_MAX_PHONES; i++) {
         if (!TASK->phones[i].busy) {
             TASK->phones[i].busy = 1;
             break;
+        }
+    }
     spinlock_unlock(&TASK->lock);
     if (i >= IPC_MAX_PHONES)
         return -1;
     return i;
+}
 /** Disconnect phone */
 void phone_dealloc(int phoneid)
+{
     spinlock_lock(&TASK->lock);
     ASSERT(TASK->phones[phoneid].busy);
     if (TASK->phones[phoneid].callee)
         ipc_phone_destroy(&TASK->phones[phoneid]);
     TASK->phones[phoneid].busy = 0;
     spinlock_unlock(&TASK->lock);
+}
+/** Connect phone to a given answerbox
+ *
+ * @param phoneid The slot that will be connected
+ *
+ * The procedure _enforces_ that the user first marks the phone
+ * busy (e.g. via phone_alloc) and then connects the phone, otherwise
+ * race condition may appear.
+ */
 void phone_connect(int phoneid, answerbox_t *box)
+{
     phone_t *phone = &TASK->phones[phoneid];
+    ASSERT(phone->busy);
     ipc_phone_connect(phone, box);
+}

Subversion Repositories HelenOS-historic

(root)/kernel/trunk/generic/src/ipc/ipcrsc.c – Rev 1083 → 1084