X-Git-Url: https://gerrit.fd.io/r/gitweb?a=blobdiff_plain;f=src%2Fsvm%2Fmessage_queue.c;h=a6af7962f73082ad17b8939632bdfad456fe5a99;hb=646984080358df8091c4fb10890a033777d90e4c;hp=89411143c1243eb1e9d1dff788847722d4842c29;hpb=3c2fed5145d9e40a9ecd178c2866c813eddc6203;p=vpp.git

diff --git a/src/svm/message_queue.c b/src/svm/message_queue.c
index 89411143c12..a6af7962f73 100644
--- a/src/svm/message_queue.c
+++ b/src/svm/message_queue.c
@@ -15,6 +15,10 @@
 
 #include <svm/message_queue.h>
 #include <vppinfra/mem.h>
+#include <vppinfra/format.h>
+#include <vppinfra/time.h>
+#include <sys/eventfd.h>
+#include <sys/socket.h>
 
 static inline svm_msg_q_ring_t *
 svm_msg_q_ring_inline (svm_msg_q_t * mq, u32 ring_index)
@@ -32,66 +36,202 @@ static inline void *
 svm_msg_q_ring_data (svm_msg_q_ring_t * ring, u32 elt_index)
 {
   ASSERT (elt_index < ring->nitems);
-  return (ring->data + elt_index * ring->elsize);
+  return (ring->shr->data + elt_index * ring->elsize);
 }
 
-svm_msg_q_t *
-svm_msg_q_alloc (svm_msg_q_cfg_t * cfg)
+static void
+svm_msg_q_init_mutex (svm_msg_q_shared_queue_t *sq)
 {
-  svm_msg_q_ring_t *ring;
-  svm_msg_q_t *mq;
-  uword size;
+  pthread_mutexattr_t attr;
+  pthread_condattr_t cattr;
+
+  clib_memset (&attr, 0, sizeof (attr));
+  clib_memset (&cattr, 0, sizeof (cattr));
+
+  if (pthread_mutexattr_init (&attr))
+    clib_unix_warning ("mutexattr_init");
+  if (pthread_mutexattr_setpshared (&attr, PTHREAD_PROCESS_SHARED))
+    clib_unix_warning ("pthread_mutexattr_setpshared");
+  if (pthread_mutexattr_setrobust (&attr, PTHREAD_MUTEX_ROBUST))
+    clib_unix_warning ("setrobust");
+  if (pthread_mutex_init (&sq->mutex, &attr))
+    clib_unix_warning ("mutex_init");
+  if (pthread_mutexattr_destroy (&attr))
+    clib_unix_warning ("mutexattr_destroy");
+  if (pthread_condattr_init (&cattr))
+    clib_unix_warning ("condattr_init");
+  if (pthread_condattr_setpshared (&cattr, PTHREAD_PROCESS_SHARED))
+    clib_unix_warning ("condattr_setpshared");
+  if (pthread_cond_init (&sq->condvar, &cattr))
+    clib_unix_warning ("cond_init1");
+  if (pthread_condattr_destroy (&cattr))
+    clib_unix_warning ("cond_init2");
+}
+
+svm_msg_q_shared_t *
+svm_msg_q_init (void *base, svm_msg_q_cfg_t *cfg)
+{
+  svm_msg_q_ring_shared_t *ring;
+  svm_msg_q_shared_queue_t *sq;
+  svm_msg_q_shared_t *smq;
+  u32 q_sz, offset;
   int i;
 
-  if (!cfg)
-    return 0;
+  q_sz = sizeof (*sq) + cfg->q_nitems * sizeof (svm_msg_q_msg_t);
 
-  mq = clib_mem_alloc_aligned (sizeof (svm_msg_q_t), CLIB_CACHE_LINE_BYTES);
-  memset (mq, 0, sizeof (*mq));
-  mq->q = svm_queue_init (cfg->q_nitems, sizeof (svm_msg_q_msg_t),
-			  cfg->consumer_pid, 0);
-  vec_validate (mq->rings, cfg->n_rings - 1);
+  smq = (svm_msg_q_shared_t *) base;
+  sq = smq->q;
+  clib_memset (sq, 0, sizeof (*sq));
+  sq->elsize = sizeof (svm_msg_q_msg_t);
+  sq->maxsize = cfg->q_nitems;
+  smq->n_rings = cfg->n_rings;
+  ring = (void *) ((u8 *) smq->q + q_sz);
   for (i = 0; i < cfg->n_rings; i++)
     {
-      ring = &mq->rings[i];
       ring->elsize = cfg->ring_cfgs[i].elsize;
       ring->nitems = cfg->ring_cfgs[i].nitems;
+      ring->cursize = ring->head = ring->tail = 0;
+      offset = sizeof (*ring) + ring->nitems * ring->elsize;
+      ring = (void *) ((u8 *) ring + offset);
+    }
+
+  svm_msg_q_init_mutex (sq);
+
+  return smq;
+}
+
+uword
+svm_msg_q_size_to_alloc (svm_msg_q_cfg_t *cfg)
+{
+  svm_msg_q_ring_cfg_t *ring_cfg;
+  uword rings_sz = 0, mq_sz;
+  u32 q_sz;
+  int i;
+
+  ASSERT (cfg);
+
+  rings_sz = sizeof (svm_msg_q_ring_shared_t) * cfg->n_rings;
+  for (i = 0; i < cfg->n_rings; i++)
+    {
       if (cfg->ring_cfgs[i].data)
-	ring->data = cfg->ring_cfgs[i].data;
-      else
-	{
-	  size = (uword) ring->nitems * ring->elsize;
-	  ring->data = clib_mem_alloc_aligned (size, CLIB_CACHE_LINE_BYTES);
-	}
+	continue;
+      ring_cfg = &cfg->ring_cfgs[i];
+      rings_sz += (uword) ring_cfg->nitems * ring_cfg->elsize;
     }
 
-  return mq;
+  q_sz = sizeof (svm_msg_q_shared_queue_t) +
+	 cfg->q_nitems * sizeof (svm_msg_q_msg_t);
+  mq_sz = sizeof (svm_msg_q_shared_t) + q_sz + rings_sz;
+
+  return mq_sz;
+}
+
+svm_msg_q_shared_t *
+svm_msg_q_alloc (svm_msg_q_cfg_t *cfg)
+{
+  uword mq_sz;
+  u8 *base;
+
+  mq_sz = svm_msg_q_size_to_alloc (cfg);
+  base = clib_mem_alloc_aligned (mq_sz, CLIB_CACHE_LINE_BYTES);
+  if (!base)
+    return 0;
+
+  return svm_msg_q_init (base, cfg);
 }
 
 void
-svm_msg_q_free (svm_msg_q_t * mq)
+svm_msg_q_attach (svm_msg_q_t *mq, void *smq_base)
 {
-  svm_msg_q_ring_t *ring;
+  svm_msg_q_ring_shared_t *ring;
+  svm_msg_q_shared_t *smq;
+  u32 i, n_rings, q_sz, offset;
 
-  vec_foreach (ring, mq->rings)
-  {
-    clib_mem_free (ring->data);
-  }
+  smq = (svm_msg_q_shared_t *) smq_base;
+  mq->q.shr = smq->q;
+  mq->q.evtfd = -1;
+  n_rings = smq->n_rings;
+  vec_validate (mq->rings, n_rings - 1);
+  q_sz = sizeof (svm_msg_q_shared_queue_t) +
+	 mq->q.shr->maxsize * sizeof (svm_msg_q_msg_t);
+  ring = (void *) ((u8 *) smq->q + q_sz);
+  for (i = 0; i < n_rings; i++)
+    {
+      mq->rings[i].nitems = ring->nitems;
+      mq->rings[i].elsize = ring->elsize;
+      mq->rings[i].shr = ring;
+      offset = sizeof (*ring) + ring->nitems * ring->elsize;
+      ring = (void *) ((u8 *) ring + offset);
+    }
+  clib_spinlock_init (&mq->q.lock);
+}
+
+void
+svm_msg_q_cleanup (svm_msg_q_t *mq)
+{
   vec_free (mq->rings);
+  clib_spinlock_free (&mq->q.lock);
+  if (mq->q.evtfd != -1)
+    close (mq->q.evtfd);
+}
+
+void
+svm_msg_q_free (svm_msg_q_t * mq)
+{
+  svm_msg_q_cleanup (mq);
+  clib_mem_free (mq->q.shr);
   clib_mem_free (mq);
 }
 
+static void
+svm_msg_q_send_signal (svm_msg_q_t *mq, u8 is_consumer)
+{
+  if (mq->q.evtfd == -1)
+    {
+      if (is_consumer)
+	{
+	  int rv = pthread_mutex_lock (&mq->q.shr->mutex);
+	  if (PREDICT_FALSE (rv == EOWNERDEAD))
+	    {
+	      rv = pthread_mutex_consistent (&mq->q.shr->mutex);
+	      return;
+	    }
+	}
+
+      (void) pthread_cond_broadcast (&mq->q.shr->condvar);
+
+      if (is_consumer)
+	pthread_mutex_unlock (&mq->q.shr->mutex);
+    }
+  else
+    {
+      int __clib_unused rv;
+      u64 data = 1;
+
+      if (mq->q.evtfd < 0)
+	return;
+
+      rv = write (mq->q.evtfd, &data, sizeof (data));
+      if (PREDICT_FALSE (rv < 0))
+	clib_unix_warning ("signal write on %d returned %d", mq->q.evtfd, rv);
+    }
+}
+
 svm_msg_q_msg_t
 svm_msg_q_alloc_msg_w_ring (svm_msg_q_t * mq, u32 ring_index)
 {
-  svm_msg_q_msg_t msg = {.as_u64 = ~0 };
-  svm_msg_q_ring_t *ring = svm_msg_q_ring_inline (mq, ring_index);
+  svm_msg_q_ring_shared_t *sr;
+  svm_msg_q_ring_t *ring;
+  svm_msg_q_msg_t msg;
+
+  ring = svm_msg_q_ring_inline (mq, ring_index);
+  sr = ring->shr;
 
-  ASSERT (ring->cursize != ring->nitems);
+  ASSERT (sr->cursize < ring->nitems);
   msg.ring_index = ring - mq->rings;
-  msg.elt_index = ring->tail;
-  ring->tail = (ring->tail + 1) % ring->nitems;
-  __sync_fetch_and_add (&ring->cursize, 1);
+  msg.elt_index = sr->tail;
+  sr->tail = (sr->tail + 1) % ring->nitems;
+  clib_atomic_fetch_add_rel (&sr->cursize, 1);
   return msg;
 }
 
@@ -103,27 +243,21 @@ svm_msg_q_lock_and_alloc_msg_w_ring (svm_msg_q_t * mq, u32 ring_index,
     {
       if (svm_msg_q_try_lock (mq))
 	return -1;
-      if (PREDICT_FALSE (svm_msg_q_ring_is_full (mq, ring_index)))
+      if (PREDICT_FALSE (svm_msg_q_is_full (mq)
+			 || svm_msg_q_ring_is_full (mq, ring_index)))
 	{
 	  svm_msg_q_unlock (mq);
 	  return -2;
 	}
       *msg = svm_msg_q_alloc_msg_w_ring (mq, ring_index);
-      if (PREDICT_FALSE (svm_msg_q_msg_is_invalid (msg)))
-	{
-	  svm_msg_q_unlock (mq);
-	  return -2;
-	}
     }
   else
     {
       svm_msg_q_lock (mq);
+      while (svm_msg_q_is_full (mq)
+	     || svm_msg_q_ring_is_full (mq, ring_index))
+	svm_msg_q_wait_prod (mq);
       *msg = svm_msg_q_alloc_msg_w_ring (mq, ring_index);
-      while (svm_msg_q_msg_is_invalid (msg))
-	{
-	  svm_msg_q_wait (mq);
-	  *msg = svm_msg_q_alloc_msg_w_ring (mq, ring_index);
-	}
     }
   return 0;
 }
@@ -132,16 +266,18 @@ svm_msg_q_msg_t
 svm_msg_q_alloc_msg (svm_msg_q_t * mq, u32 nbytes)
 {
   svm_msg_q_msg_t msg = {.as_u64 = ~0 };
+  svm_msg_q_ring_shared_t *sr;
   svm_msg_q_ring_t *ring;
 
   vec_foreach (ring, mq->rings)
   {
-    if (ring->elsize < nbytes || ring->cursize == ring->nitems)
+    sr = ring->shr;
+    if (ring->elsize < nbytes || sr->cursize == ring->nitems)
       continue;
     msg.ring_index = ring - mq->rings;
-    msg.elt_index = ring->tail;
-    ring->tail = (ring->tail + 1) % ring->nitems;
-    __sync_fetch_and_add (&ring->cursize, 1);
+    msg.elt_index = sr->tail;
+    sr->tail = (sr->tail + 1) % ring->nitems;
+    clib_atomic_fetch_add_relax (&sr->cursize, 1);
     break;
   }
   return msg;
@@ -157,66 +293,348 @@ svm_msg_q_msg_data (svm_msg_q_t * mq, svm_msg_q_msg_t * msg)
 void
 svm_msg_q_free_msg (svm_msg_q_t * mq, svm_msg_q_msg_t * msg)
 {
+  svm_msg_q_ring_shared_t *sr;
   svm_msg_q_ring_t *ring;
+  u32 need_signal;
 
-  if (vec_len (mq->rings) <= msg->ring_index)
-    return;
-  ring = &mq->rings[msg->ring_index];
-  if (msg->elt_index == ring->head)
+  ASSERT (vec_len (mq->rings) > msg->ring_index);
+  ring = svm_msg_q_ring_inline (mq, msg->ring_index);
+  sr = ring->shr;
+  if (msg->elt_index == sr->head)
     {
-      ring->head = (ring->head + 1) % ring->nitems;
+      sr->head = (sr->head + 1) % ring->nitems;
     }
   else
     {
+      clib_warning ("message out of order: elt %u head %u ring %u",
+		    msg->elt_index, sr->head, msg->ring_index);
       /* for now, expect messages to be processed in order */
       ASSERT (0);
     }
-  __sync_fetch_and_sub (&ring->cursize, 1);
+
+  need_signal = clib_atomic_load_relax_n (&sr->cursize) == ring->nitems;
+  clib_atomic_fetch_sub_relax (&sr->cursize, 1);
+
+  if (PREDICT_FALSE (need_signal))
+    svm_msg_q_send_signal (mq, 1 /* is consumer */);
 }
 
 static int
 svm_msq_q_msg_is_valid (svm_msg_q_t * mq, svm_msg_q_msg_t * msg)
 {
+  u32 dist1, dist2, tail, head;
+  svm_msg_q_ring_shared_t *sr;
   svm_msg_q_ring_t *ring;
-  u32 dist1, dist2;
 
   if (vec_len (mq->rings) <= msg->ring_index)
     return 0;
-  ring = &mq->rings[msg->ring_index];
 
-  dist1 = ((ring->nitems + msg->elt_index) - ring->head) % ring->nitems;
-  if (ring->tail == ring->head)
-    dist2 = (ring->cursize == 0) ? 0 : ring->nitems;
+  ring = svm_msg_q_ring_inline (mq, msg->ring_index);
+  sr = ring->shr;
+  tail = sr->tail;
+  head = sr->head;
+
+  dist1 = ((ring->nitems + msg->elt_index) - head) % ring->nitems;
+  if (tail == head)
+    dist2 = (sr->cursize == 0) ? 0 : ring->nitems;
   else
-    dist2 = ((ring->nitems + ring->tail) - ring->head) % ring->nitems;
+    dist2 = ((ring->nitems + tail) - head) % ring->nitems;
   return (dist1 < dist2);
 }
 
+static void
+svm_msg_q_add_raw (svm_msg_q_t *mq, u8 *elem)
+{
+  svm_msg_q_shared_queue_t *sq = mq->q.shr;
+  i8 *tailp;
+  u32 sz;
+
+  tailp = (i8 *) (&sq->data[0] + sq->elsize * sq->tail);
+  clib_memcpy_fast (tailp, elem, sq->elsize);
+
+  sq->tail = (sq->tail + 1) % sq->maxsize;
+
+  sz = clib_atomic_fetch_add_rel (&sq->cursize, 1);
+  if (!sz)
+    svm_msg_q_send_signal (mq, 0 /* is consumer */);
+}
+
 int
 svm_msg_q_add (svm_msg_q_t * mq, svm_msg_q_msg_t * msg, int nowait)
 {
   ASSERT (svm_msq_q_msg_is_valid (mq, msg));
-  return svm_queue_add (mq->q, (u8 *) msg, nowait);
+
+  if (nowait)
+    {
+      /* zero on success */
+      if (svm_msg_q_try_lock (mq))
+	{
+	  return (-1);
+	}
+    }
+  else
+    svm_msg_q_lock (mq);
+
+  if (PREDICT_FALSE (svm_msg_q_is_full (mq)))
+    {
+      if (nowait)
+	return (-2);
+      while (svm_msg_q_is_full (mq))
+	svm_msg_q_wait_prod (mq);
+    }
+
+  svm_msg_q_add_raw (mq, (u8 *) msg);
+
+  svm_msg_q_unlock (mq);
+
+  return 0;
 }
 
 void
-svm_msg_q_add_w_lock (svm_msg_q_t * mq, svm_msg_q_msg_t * msg)
+svm_msg_q_add_and_unlock (svm_msg_q_t * mq, svm_msg_q_msg_t * msg)
 {
   ASSERT (svm_msq_q_msg_is_valid (mq, msg));
-  svm_queue_add_raw (mq->q, (u8 *) msg);
+  svm_msg_q_add_raw (mq, (u8 *) msg);
+  svm_msg_q_unlock (mq);
+}
+
+int
+svm_msg_q_sub_raw (svm_msg_q_t *mq, svm_msg_q_msg_t *elem)
+{
+  svm_msg_q_shared_queue_t *sq = mq->q.shr;
+  i8 *headp;
+  u32 sz;
+
+  ASSERT (!svm_msg_q_is_empty (mq));
+
+  headp = (i8 *) (&sq->data[0] + sq->elsize * sq->head);
+  clib_memcpy_fast (elem, headp, sq->elsize);
+
+  sq->head = (sq->head + 1) % sq->maxsize;
+
+  sz = clib_atomic_fetch_sub_relax (&sq->cursize, 1);
+  if (PREDICT_FALSE (sz == sq->maxsize))
+    svm_msg_q_send_signal (mq, 1 /* is consumer */);
+
+  return 0;
 }
 
 int
-svm_msg_q_sub (svm_msg_q_t * mq, svm_msg_q_msg_t * msg,
+svm_msg_q_sub_raw_batch (svm_msg_q_t *mq, svm_msg_q_msg_t *msg_buf, u32 n_msgs)
+{
+  svm_msg_q_shared_queue_t *sq = mq->q.shr;
+  u32 sz, to_deq;
+  i8 *headp;
+
+  sz = svm_msg_q_size (mq);
+  ASSERT (sz);
+  to_deq = clib_min (sz, n_msgs);
+
+  headp = (i8 *) (&sq->data[0] + sq->elsize * sq->head);
+
+  if (sq->head + to_deq < sq->maxsize)
+    {
+      clib_memcpy_fast (msg_buf, headp, sq->elsize * to_deq);
+      sq->head += to_deq;
+    }
+  else
+    {
+      u32 first_batch = sq->maxsize - sq->head;
+      clib_memcpy_fast (msg_buf, headp, sq->elsize * first_batch);
+      clib_memcpy_fast (msg_buf + first_batch, sq->data,
+			sq->elsize * (to_deq - first_batch));
+      sq->head = (sq->head + to_deq) % sq->maxsize;
+    }
+
+  clib_atomic_fetch_sub_relax (&sq->cursize, to_deq);
+  if (PREDICT_FALSE (sz == sq->maxsize))
+    svm_msg_q_send_signal (mq, 1 /* is consumer */);
+
+  return to_deq;
+}
+
+int
+svm_msg_q_sub (svm_msg_q_t *mq, svm_msg_q_msg_t *msg,
 	       svm_q_conditional_wait_t cond, u32 time)
 {
-  return svm_queue_sub (mq->q, (u8 *) msg, cond, time);
+  int rc = 0;
+
+  if (svm_msg_q_is_empty (mq))
+    {
+      if (cond == SVM_Q_NOWAIT)
+	{
+	  return (-2);
+	}
+      else if (cond == SVM_Q_TIMEDWAIT)
+	{
+	  if ((rc = svm_msg_q_timedwait (mq, time)))
+	    return rc;
+	}
+      else
+	{
+	  svm_msg_q_wait (mq, SVM_MQ_WAIT_EMPTY);
+	}
+    }
+
+  svm_msg_q_sub_raw (mq, msg);
+
+  return 0;
 }
 
 void
-svm_msg_q_sub_w_lock (svm_msg_q_t * mq, svm_msg_q_msg_t * msg)
+svm_msg_q_set_eventfd (svm_msg_q_t *mq, int fd)
+{
+  mq->q.evtfd = fd;
+}
+
+int
+svm_msg_q_alloc_eventfd (svm_msg_q_t *mq)
+{
+  int fd;
+  if ((fd = eventfd (0, 0)) < 0)
+    return -1;
+  svm_msg_q_set_eventfd (mq, fd);
+  return 0;
+}
+
+int
+svm_msg_q_wait (svm_msg_q_t *mq, svm_msg_q_wait_type_t type)
 {
-  svm_queue_sub_raw (mq->q, (u8 *) msg);
+  u8 (*fn) (svm_msg_q_t *);
+  int rv;
+
+  fn = (type == SVM_MQ_WAIT_EMPTY) ? svm_msg_q_is_empty : svm_msg_q_is_full;
+
+  if (mq->q.evtfd == -1)
+    {
+      rv = pthread_mutex_lock (&mq->q.shr->mutex);
+      if (PREDICT_FALSE (rv == EOWNERDEAD))
+	{
+	  rv = pthread_mutex_consistent (&mq->q.shr->mutex);
+	  return rv;
+	}
+
+      while (fn (mq))
+	pthread_cond_wait (&mq->q.shr->condvar, &mq->q.shr->mutex);
+
+      pthread_mutex_unlock (&mq->q.shr->mutex);
+    }
+  else
+    {
+      u64 buf;
+
+      while (fn (mq))
+	{
+	  while ((rv = read (mq->q.evtfd, &buf, sizeof (buf))) < 0)
+	    {
+	      if (errno != EAGAIN)
+		{
+		  clib_unix_warning ("read error");
+		  return rv;
+		}
+	    }
+	}
+    }
+
+  return 0;
+}
+
+int
+svm_msg_q_wait_prod (svm_msg_q_t *mq)
+{
+  if (mq->q.evtfd == -1)
+    {
+      while (svm_msg_q_is_full (mq))
+	pthread_cond_wait (&mq->q.shr->condvar, &mq->q.shr->mutex);
+    }
+  else
+    {
+      u64 buf;
+      int rv;
+
+      while (svm_msg_q_is_full (mq))
+	{
+	  while ((rv = read (mq->q.evtfd, &buf, sizeof (buf))) < 0)
+	    {
+	      if (errno != EAGAIN)
+		{
+		  clib_unix_warning ("read error");
+		  return rv;
+		}
+	    }
+	}
+    }
+
+  return 0;
+}
+
+int
+svm_msg_q_timedwait (svm_msg_q_t *mq, double timeout)
+{
+  if (mq->q.evtfd == -1)
+    {
+      svm_msg_q_shared_queue_t *sq = mq->q.shr;
+      struct timespec ts;
+      u32 sz;
+      int rv;
+
+      rv = pthread_mutex_lock (&sq->mutex);
+      if (PREDICT_FALSE (rv == EOWNERDEAD))
+	{
+	  rv = pthread_mutex_consistent (&sq->mutex);
+	  return rv;
+	}
+
+      /* check if we're still in a signalable state after grabbing lock */
+      sz = svm_msg_q_size (mq);
+      if (sz != 0 && sz != sq->maxsize)
+	{
+	  pthread_mutex_unlock (&sq->mutex);
+	  return 0;
+	}
+
+      ts.tv_sec = unix_time_now () + (u32) timeout;
+      ts.tv_nsec = (timeout - (u32) timeout) * 1e9;
+      rv = pthread_cond_timedwait (&sq->condvar, &sq->mutex, &ts);
+
+      pthread_mutex_unlock (&sq->mutex);
+      return rv;
+    }
+  else
+    {
+      struct timeval tv;
+      u64 buf;
+      int rv;
+
+      tv.tv_sec = (u64) timeout;
+      tv.tv_usec = ((u64) timeout - (u64) timeout) * 1e9;
+      rv = setsockopt (mq->q.evtfd, SOL_SOCKET, SO_RCVTIMEO,
+		       (const char *) &tv, sizeof tv);
+      if (rv < 0)
+	{
+	  clib_unix_warning ("setsockopt");
+	  return -1;
+	}
+
+      rv = read (mq->q.evtfd, &buf, sizeof (buf));
+      if (rv < 0)
+	clib_warning ("read %u", errno);
+
+      return rv < 0 ? errno : 0;
+    }
+}
+
+u8 *
+format_svm_msg_q (u8 * s, va_list * args)
+{
+  svm_msg_q_t *mq = va_arg (*args, svm_msg_q_t *);
+  s = format (s, " [Q:%d/%d]", mq->q.shr->cursize, mq->q.shr->maxsize);
+  for (u32 i = 0; i < vec_len (mq->rings); i++)
+    {
+      s = format (s, " [R%d:%d/%d]", i, mq->rings[i].shr->cursize,
+		  mq->rings[i].nitems);
+    }
+  return s;
 }
 
 /*