lib/libblockdriver/mq.c

   1 /* This file contains a simple message queue implementation to support both
   2  * the singlethread and the multithreaded driver implementation.
   3  *
   4  * Changes:
   5  *   Oct 27, 2011   rewritten to use sys/queue.h (D.C. van Moolenbroek)
   6  *   Aug 27, 2011   integrated into libblockdriver (A. Welzel)
   7  */
   8
   9 #include <minix/blockdriver_mt.h>
  10 #include <sys/queue.h>
  11 #include <assert.h>
  12
  13 #include "const.h"
  14 #include "mq.h"
  15
  16 #define MQ_SIZE         128
  17
  18 struct mq_cell {
  19   message mess;
  20   int ipc_status;
  21   STAILQ_ENTRY(mq_cell) next;
  22 };
  23
  24 static struct mq_cell pool[MQ_SIZE];
  25 static STAILQ_HEAD(queue, mq_cell) queue[MAX_DEVICES];
  26 static STAILQ_HEAD(free_list, mq_cell) free_list;
  27
  28 /*===========================================================================*
  29  *                              mq_init                                      *
  30  *===========================================================================*/
  31 void mq_init(void)
  32 {
  33 /* Initialize the message queues and message cells.
  34  */
  35   int i;
  36
  37   STAILQ_INIT(&free_list);
  38
  39   for (i = 0; i < MAX_DEVICES; i++)
  40         STAILQ_INIT(&queue[i]);
  41
  42   for (i = 0; i < MQ_SIZE; i++)
  43         STAILQ_INSERT_HEAD(&free_list, &pool[i], next);
  44 }
  45
  46 /*===========================================================================*
  47  *                              mq_enqueue                                   *
  48  *===========================================================================*/
  49 int mq_enqueue(device_id_t device_id, const message *mess,
  50   int ipc_status)
  51 {
  52 /* Add a message, including its IPC status, to the message queue of a device.
  53  * Return TRUE iff the message was added successfully.
  54  */
  55   struct mq_cell *cell;
  56
  57   assert(device_id >= 0 && device_id < MAX_DEVICES);
  58
  59   if (STAILQ_EMPTY(&free_list))
  60         return FALSE;
  61
  62   cell = STAILQ_FIRST(&free_list);
  63   STAILQ_REMOVE_HEAD(&free_list, next);
  64
  65   cell->mess = *mess;
  66   cell->ipc_status = ipc_status;
  67
  68   STAILQ_INSERT_TAIL(&queue[device_id], cell, next);
  69
  70   return TRUE;
  71 }
  72
  73 /*===========================================================================*
  74  *                              mq_dequeue                                   *
  75  *===========================================================================*/
  76 int mq_dequeue(device_id_t device_id, message *mess, int *ipc_status)
  77 {
  78 /* Return and remove a message, including its IPC status, from the message
  79  * queue of a thread. Return TRUE iff a message was available.
  80  */
  81   struct mq_cell *cell;
  82
  83   assert(device_id >= 0 && device_id < MAX_DEVICES);
  84
  85   if (STAILQ_EMPTY(&queue[device_id]))
  86         return FALSE;
  87
  88   cell = STAILQ_FIRST(&queue[device_id]);
  89   STAILQ_REMOVE_HEAD(&queue[device_id], next);
  90
  91   *mess = cell->mess;
  92   *ipc_status = cell->ipc_status;
  93
  94   STAILQ_INSERT_HEAD(&free_list, cell, next);
  95
  96   return TRUE;
  97 }