VCL: add epoll_* functions.

Change-Id: Ife27795ea96919c116fb6ff33d106663b54df72d
Signed-off-by: Dave Wallace <dwallacelf@gmail.com>

4 files changed, 813 insertions, 85 deletions

diff --git a/src/uri/sock_test_client.c b/src/uri/sock_test_client.c
index 151c90b2960..b53f8f2230f 100644
--- a/src/uri/sock_test_client.c
+++ b/src/uri/sock_test_client.c
@@ -505,7 +505,7 @@ sock_test_connect_test_sockets (uint32_t num_test_sockets)
 #ifdef VCL_TEST
 	  tsock->fd =
 	    vppcom_session_create (VPPCOM_VRF_DEFAULT, VPPCOM_PROTO_TCP,
-				   0 /* is_nonblocking */ );
+				   1 /* is_nonblocking */ );
 	  if (tsock->fd < 0)
 	    {
 	      errno = -tsock->fd;
diff --git a/src/uri/sock_test_server.c b/src/uri/sock_test_server.c
index 35046aa061b..e5b5a56e8d6 100644
--- a/src/uri/sock_test_server.c
+++ b/src/uri/sock_test_server.c
@@ -23,6 +23,12 @@
 #include <ctype.h>
 #include <uri/sock_test.h>
 
+#define SOCK_SERVER_USE_EPOLL 1
+
+#if SOCK_SERVER_USE_EPOLL
+#include <sys/epoll.h>
+#endif
+
 typedef struct
 {
   uint8_t is_alloc;
@@ -38,9 +44,15 @@ typedef struct
 } sock_server_conn_t;
 
 #define SOCK_SERVER_MAX_TEST_CONN  10
+#define SOCK_SERVER_MAX_EPOLL_EVENTS 10
 typedef struct
 {
   int listen_fd;
+#if SOCK_SERVER_USE_EPOLL
+  int epfd;
+  struct epoll_event listen_ev;
+  struct epoll_event wait_events[SOCK_SERVER_MAX_EPOLL_EVENTS];
+#endif
   size_t num_conn;
   size_t conn_pool_size;
   sock_server_conn_t *conn_pool;
@@ -52,6 +64,7 @@ typedef struct
 
 sock_server_main_t sock_server_main;
 
+#if ! SOCK_SERVER_USE_EPOLL
 static inline int
 get_nfds (void)
 {
@@ -83,6 +96,7 @@ conn_fdset_clr (sock_server_conn_t * conn, fd_set * fdset)
   FD_CLR (conn->fd, fdset);
   ssm->nfds = get_nfds ();
 }
+#endif
 
 static inline void
 conn_pool_expand (size_t expand_size)
@@ -141,10 +155,12 @@ conn_pool_alloc (void)
 static inline void
 conn_pool_free (sock_server_conn_t * conn)
 {
+#if ! SOCK_SERVER_USE_EPOLL
   sock_server_main_t *ssm = &sock_server_main;
 
   conn_fdset_clr (conn, &ssm->rd_fdset);
   conn_fdset_clr (conn, &ssm->wr_fdset);
+#endif
   conn->fd = 0;
   conn->is_alloc = 0;
 }
@@ -274,6 +290,8 @@ new_client (void)
 #ifdef VCL_TEST
   client_fd = vppcom_session_accept (ssm->listen_fd, &conn->endpt,
 				     -1.0 /* wait forever */ );
+  if (client_fd < 0)
+    errno = -client_fd;
 #else
   client_fd = accept (ssm->listen_fd, (struct sockaddr *) NULL, NULL);
 #endif
@@ -281,7 +299,7 @@ new_client (void)
     {
       int errno_val;
       errno_val = errno;
-      perror ("ERROR in main()");
+      perror ("ERROR in new_client()");
       fprintf (stderr, "ERROR: accept failed (errno = %d)!\n", errno_val);
     }
 
@@ -289,7 +307,36 @@ new_client (void)
 	  client_fd, client_fd);
 
   conn->fd = client_fd;
+
+#if ! SOCK_SERVER_USE_EPOLL
   conn_fdset_set (conn, &ssm->rd_fdset);
+  ssm->nfds++;
+#else
+  {
+    struct epoll_event ev;
+    int rv;
+
+    ev.events = EPOLLIN;
+    ev.data.u64 = conn - ssm->conn_pool;
+#ifdef VCL_TEST
+    rv = vppcom_epoll_ctl (ssm->epfd, EPOLL_CTL_ADD, client_fd, &ev);
+    if (rv)
+      errno = -rv;
+#else
+    rv = epoll_ctl (ssm->epfd, EPOLL_CTL_ADD, client_fd, &ev);
+#endif
+    if (rv < 0)
+      {
+	int errno_val;
+	errno_val = errno;
+	perror ("ERROR in new_client()");
+	fprintf (stderr, "ERROR: epoll_ctl failed (errno = %d)!\n",
+		 errno_val);
+      }
+    else
+      ssm->nfds++;
+  }
+#endif
 }
 
 int
@@ -306,12 +353,16 @@ main (int argc, char **argv)
   int errno_val;
   int v, i;
   uint16_t port = SOCK_TEST_SERVER_PORT;
+#if ! SOCK_SERVER_USE_EPOLL
   fd_set _rfdset, *rfdset = &_rfdset;
+#endif
 #ifdef VCL_TEST
   vppcom_endpt_t endpt;
 #else
+#if ! SOCK_SERVER_USE_EPOLL
   fd_set _wfdset, *wfdset = &_wfdset;
 #endif
+#endif
 
   if ((argc == 2) && (sscanf (argv[1], "%d", &v) == 1))
     port = (uint16_t) v;
@@ -390,16 +441,55 @@ main (int argc, char **argv)
       return rv;
     }
 
+  printf ("\nSERVER: Waiting for a client to connect on port %d...\n", port);
+
+#if ! SOCK_SERVER_USE_EPOLL
+
   FD_ZERO (&ssm->wr_fdset);
   FD_ZERO (&ssm->rd_fdset);
 
   FD_SET (ssm->listen_fd, &ssm->rd_fdset);
   ssm->nfds = ssm->listen_fd + 1;
 
-  printf ("\nSERVER: Waiting for a client to connect on port %d...\n", port);
+#else
+#ifdef VCL_TEST
+  ssm->epfd = vppcom_epoll_create ();
+  if (ssm->epfd < 0)
+    errno = -ssm->epfd;
+#else
+  ssm->epfd = epoll_create (1);
+#endif
+  if (ssm->epfd < 0)
+    {
+      errno_val = errno;
+      perror ("ERROR in main()");
+      fprintf (stderr, "ERROR: epoll_create failed (errno = %d)!\n",
+	       errno_val);
+      return ssm->epfd;
+    }
+
+  ssm->listen_ev.events = EPOLLIN;
+  ssm->listen_ev.data.u32 = ~0;
+#ifdef VCL_TEST
+  rv = vppcom_epoll_ctl (ssm->epfd, EPOLL_CTL_ADD, ssm->listen_fd,
+			 &ssm->listen_ev);
+  if (rv < 0)
+    errno = -rv;
+#else
+  rv = epoll_ctl (ssm->epfd, EPOLL_CTL_ADD, ssm->listen_fd, &ssm->listen_ev);
+#endif
+  if (rv < 0)
+    {
+      errno_val = errno;
+      perror ("ERROR in main()");
+      fprintf (stderr, "ERROR: epoll_ctl failed (errno = %d)!\n", errno_val);
+      return rv;
+    }
+#endif
 
   while (1)
     {
+#if ! SOCK_SERVER_USE_EPOLL
       _rfdset = ssm->rd_fdset;
 
 #ifdef VCL_TEST
@@ -431,9 +521,45 @@ main (int argc, char **argv)
 	    continue;
 
 	  conn = &ssm->conn_pool[i];
+#else
+      int num_ev;
+#ifdef VCL_TEST
+      num_ev = vppcom_epoll_wait (ssm->epfd, ssm->wait_events,
+				  SOCK_SERVER_MAX_EPOLL_EVENTS, 60.0);
+      if (rv < 0)
+	errno = -rv;
+#else
+      num_ev = epoll_wait (ssm->epfd, ssm->wait_events,
+			   SOCK_SERVER_MAX_EPOLL_EVENTS, 60000);
+#endif
+      if (num_ev < 0)
+	{
+	  perror ("epoll_wait()");
+	  fprintf (stderr, "\nERROR: epoll_wait() failed -- aborting!\n");
+	  main_rv = -1;
+	  goto done;
+	}
+      if (num_ev == 0)
+	{
+	  fprintf (stderr, "\nepoll_wait() timeout!\n");
+	  continue;
+	}
+      for (i = 0; i < num_ev; i++)
+	{
+	  if (ssm->wait_events[i].data.u32 == ~0)
+	    {
+	      new_client ();
+	      continue;
+	    }
+	  conn = &ssm->conn_pool[ssm->wait_events[i].data.u32];
+#endif
 	  client_fd = conn->fd;
 
+#if ! SOCK_SERVER_USE_EPOLL
 	  if (FD_ISSET (client_fd, rfdset))
+#else
+	  if (EPOLLIN & ssm->wait_events[i].events)
+#endif
 	    {
 	      rx_bytes = sock_test_read (client_fd, conn->buf,
 					 conn->buf_size, &conn->stats);
@@ -489,8 +615,12 @@ main (int argc, char **argv)
 			  close (client_fd);
 #endif
 			  conn_pool_free (conn);
-
+#if ! SOCK_SERVER_USE_EPOLL
 			  if (ssm->nfds == (ssm->listen_fd + 1))
+#else
+			  ssm->nfds--;
+			  if (!ssm->nfds)
+#endif
 			    {
 			      printf ("SERVER: All client connections "
 				      "closed.\n\nSERVER: "
@@ -520,7 +650,7 @@ main (int argc, char **argv)
 		      ((char *) conn->buf)[rx_bytes <
 					   conn->buf_size ? rx_bytes :
 					   conn->buf_size - 1] = 0;
-		      printf ("\nSERVER (fd %d): RX (%d bytes) - '%s'\n",
+		      printf ("SERVER (fd %d): RX (%d bytes) - '%s'\n",
 			      conn->fd, rx_bytes, conn->buf);
 		    }
 		}
diff --git a/src/uri/vppcom.c b/src/uri/vppcom.c
index 8aeb9dafa6d..127d511820a 100644
--- a/src/uri/vppcom.c
+++ b/src/uri/vppcom.c
@@ -68,6 +68,18 @@ typedef enum
   STATE_FAILED
 } session_state_t;
 
+typedef struct epoll_event vppcom_epoll_event_t;
+
+typedef struct
+{
+  u32 next_sid;
+  u32 prev_sid;
+  u32 vep_idx;
+  vppcom_epoll_event_t ev;
+#define VEP_DEFAULT_ET_MASK  (EPOLLIN|EPOLLOUT)
+  u32 et_mask;
+} vppcom_epoll_t;
+
 typedef struct
 {
   volatile session_state_t state;
@@ -79,10 +91,15 @@ typedef struct
   unix_shared_memory_queue_t *vpp_event_queue;
 
   /* Socket configuration state */
+  /* TBD: covert 'is_*' vars to bit in u8 flags; */
   u8 is_server;
   u8 is_listen;
   u8 is_cut_thru;
   u8 is_nonblocking;
+  u8 is_vep;
+  u8 is_vep_session;
+  u32 wait_cont_idx;
+  vppcom_epoll_t vep;
   u32 vrf;
   u8 is_ip4;
   u8 ip[16];
@@ -238,7 +255,7 @@ vppcom_session_at_index (u32 session_index, session_t * volatile *sess)
   if (PREDICT_FALSE ((session_index == ~0) ||
 		     pool_is_free_index (vcm->sessions, session_index)))
     {
-      clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+      clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		    vcm->my_pid, session_index);
       return VPPCOM_EBADFD;
     }
@@ -554,7 +571,7 @@ vl_api_disconnect_session_reply_t_handler (vl_api_disconnect_session_reply_t *
       if (PREDICT_FALSE (rv))
 	{
 	  if (VPPCOM_DEBUG > 1)
-	    clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	    clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 			  vcm->my_pid, p[0]);
 	}
       hash_unset (vcm->session_index_by_vpp_handles, mp->handle);
@@ -616,7 +633,7 @@ vl_api_disconnect_session_t_handler (vl_api_disconnect_session_t * mp)
       if (PREDICT_FALSE (rval))
 	{
 	  if (VPPCOM_DEBUG > 1)
-	    clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	    clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 			  vcm->my_pid, p[0]);
 	}
       else
@@ -658,7 +675,7 @@ vl_api_reset_session_t_handler (vl_api_reset_session_t * mp)
       if (PREDICT_FALSE (rval))
 	{
 	  if (VPPCOM_DEBUG > 1)
-	    clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	    clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 			  vcm->my_pid, p[0]);
 	}
       else
@@ -729,6 +746,7 @@ vl_api_connect_session_reply_t_handler (vl_api_connect_session_reply_t * mp)
       vec_reset_length (a->new_segment_indices);
       if (PREDICT_FALSE (rv))
 	{
+	  clib_spinlock_unlock (&vcm->sessions_lockp);
 	  clib_warning ("[%d] sm_fifo_segment_attach ('%s') failed",
 			vcm->my_pid, a->segment_name);
 	  return;
@@ -802,7 +820,7 @@ vppcom_send_disconnect (u32 session_index)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 1)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, session_index);
       return rv;
     }
@@ -993,12 +1011,12 @@ vl_api_accept_session_t_handler (vl_api_accept_session_t * mp)
   session->port = ntohs (mp->port);
   session->is_ip4 = mp->is_ip4;
   clib_memcpy (session->ip, mp->ip, sizeof (session->ip));
-  clib_spinlock_unlock (&vcm->sessions_lockp);
 
   /* Add it to lookup table */
   hash_set (vcm->session_index_by_vpp_handles, mp->handle, session_index);
 
   clib_fifo_add1 (vcm->client_session_index_fifo, session_index);
+  clib_spinlock_unlock (&vcm->sessions_lockp);
 
   /*
    * Send accept reply to vpp
@@ -1031,11 +1049,13 @@ vl_api_connect_sock_t_handler (vl_api_connect_sock_t * mp)
   svm_fifo_t *tx_fifo;
   unix_shared_memory_queue_t *event_q = 0;
 
+  clib_spinlock_lock (&vcm->sessions_lockp);
   if (!clib_fifo_free_elts (vcm->client_session_index_fifo))
     {
       if (VPPCOM_DEBUG > 1)
 	clib_warning ("[%d] client session queue is full!", vcm->my_pid);
       rv = VNET_API_ERROR_QUEUE_FULL;
+      clib_spinlock_unlock (&vcm->sessions_lockp);
       goto send_reply;
     }
 
@@ -1063,7 +1083,6 @@ vl_api_connect_sock_t_handler (vl_api_connect_sock_t * mp)
   if (VPPCOM_DEBUG > 1)
     clib_warning ("[%d] created segment '%s'", vcm->my_pid, a->segment_name);
 
-  clib_spinlock_lock (&vcm->sessions_lockp);
   pool_get (vcm->sessions, session);
   memset (session, 0, sizeof (*session));
   session_index = session - vcm->sessions;
@@ -1127,8 +1146,8 @@ vl_api_connect_sock_t_handler (vl_api_connect_sock_t * mp)
   if (VPPCOM_DEBUG > 1)
     clib_warning ("[%d] Connected cut-thru to client: sid %d",
 		  vcm->my_pid, session_index);
-  clib_spinlock_unlock (&vcm->sessions_lockp);
   clib_fifo_add1 (vcm->client_session_index_fifo, session_index);
+  clib_spinlock_unlock (&vcm->sessions_lockp);
 
 send_reply:
   rmp = vl_msg_api_alloc (sizeof (*rmp));
@@ -1191,7 +1210,7 @@ vppcom_send_unbind_sock (u32 session_index)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, session_index);
       return;
     }
@@ -1234,7 +1253,7 @@ vppcom_session_unbind (u32 session_index)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 1)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, session_index);
       return VPPCOM_EBADFD;
     }
@@ -1807,6 +1826,7 @@ vppcom_session_create (u32 vrf, u8 proto, u8 is_nonblocking)
 
   clib_spinlock_lock (&vcm->sessions_lockp);
   pool_get (vcm->sessions, session);
+  memset (session, 0, sizeof (*session));
   session_index = session - vcm->sessions;
 
   session->vrf = vrf;
@@ -1832,49 +1852,101 @@ vppcom_session_close (uint32_t session_index)
   rv = vppcom_session_at_index (session_index, &session);
   if (PREDICT_FALSE (rv))
     {
-      clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, session_index);
-      return rv;
+      clib_spinlock_unlock (&vcm->sessions_lockp);
+      goto done;
     }
   clib_spinlock_unlock (&vcm->sessions_lockp);
 
   if (VPPCOM_DEBUG > 0)
     clib_warning ("[%d] sid %d", vcm->my_pid, session_index);
 
-  if (session->is_cut_thru)
+  if (session->is_vep)
     {
-      if (session->is_server)
+      u32 next_sid;
+      for (next_sid = session->vep.next_sid; next_sid != ~0;
+	   next_sid = session->vep.next_sid)
 	{
-	  rv = vppcom_session_unbind_cut_thru (session);
+	  rv = vppcom_epoll_ctl (session_index, EPOLL_CTL_DEL, next_sid, 0);
 	  if ((VPPCOM_DEBUG > 0) && (rv < 0))
-	    clib_warning ("[%d] unbind cut-thru (session %d) failed, "
-			  "rv = %s (%d)",
+	    clib_warning ("[%d] EPOLL_CTL_DEL vep_idx %u, sid %u failed, "
+			  "rv = %s (%d)", session_index, next_sid,
 			  vcm->my_pid, session_index,
 			  vppcom_retval_str (rv), rv);
+
+	  clib_spinlock_lock (&vcm->sessions_lockp);
+	  rv = vppcom_session_at_index (session_index, &session);
+	  if (PREDICT_FALSE (rv))
+	    {
+	      if (VPPCOM_DEBUG > 0)
+		clib_warning
+		  ("[%d] invalid session, sid (%u) has been closed!",
+		   vcm->my_pid, session_index);
+	      clib_spinlock_unlock (&vcm->sessions_lockp);
+	      goto done;
+	    }
+	  clib_spinlock_unlock (&vcm->sessions_lockp);
 	}
     }
-  else if (session->is_server)
-    {
-      rv = vppcom_session_unbind (session_index);
-      if ((VPPCOM_DEBUG > 0) && (rv < 0))
-	clib_warning ("[%d] unbind (session %d) failed, rv = %s (%d)",
-		      vcm->my_pid, session_index, vppcom_retval_str (rv), rv);
-    }
   else
     {
-      rv = vppcom_session_disconnect (session_index);
-      if ((VPPCOM_DEBUG > 0) && (rv < 0))
-	clib_warning ("[%d] disconnect (session %d) failed, rv = %s (%d)",
-		      vcm->my_pid, session_index, vppcom_retval_str (rv), rv);
-    }
-  if (rv < 0)
-    return rv;
+      if (session->is_vep_session)
+	{
+	  u32 vep_idx = session->vep.vep_idx;
+	  rv = vppcom_epoll_ctl (vep_idx, EPOLL_CTL_DEL, session_index, 0);
+	  if ((VPPCOM_DEBUG > 0) && (rv < 0))
+	    clib_warning ("[%d] EPOLL_CTL_DEL vep_idx %u, sid %u failed, "
+			  "rv = %s (%d)", vep_idx, session_index,
+			  vcm->my_pid, session_index,
+			  vppcom_retval_str (rv), rv);
 
-  clib_spinlock_lock (&vcm->sessions_lockp);
+	  clib_spinlock_lock (&vcm->sessions_lockp);
+	  rv = vppcom_session_at_index (session_index, &session);
+	  if (PREDICT_FALSE (rv))
+	    {
+	      if (VPPCOM_DEBUG > 0)
+		clib_warning
+		  ("[%d] invalid session, sid (%u) has been closed!",
+		   vcm->my_pid, session_index);
+	      clib_spinlock_unlock (&vcm->sessions_lockp);
+	      goto done;
+	    }
+	  clib_spinlock_unlock (&vcm->sessions_lockp);
+	}
+
+      if (session->is_cut_thru)
+	{
+	  if (session->is_server)
+	    {
+	      rv = vppcom_session_unbind_cut_thru (session);
+	      if ((VPPCOM_DEBUG > 0) && (rv < 0))
+		clib_warning ("[%d] unbind cut-thru (session %d) failed, "
+			      "rv = %s (%d)",
+			      vcm->my_pid, session_index,
+			      vppcom_retval_str (rv), rv);
+	    }
+	}
+      else if (session->is_server)
+	{
+	  rv = vppcom_session_unbind (session_index);
+	  if ((VPPCOM_DEBUG > 0) && (rv < 0))
+	    clib_warning ("[%d] unbind (session %d) failed, rv = %s (%d)",
+			  vcm->my_pid, session_index,
+			  vppcom_retval_str (rv), rv);
+	}
+      else
+	{
+	  rv = vppcom_session_disconnect (session_index);
+	  if ((VPPCOM_DEBUG > 0) && (rv < 0))
+	    clib_warning ("[%d] disconnect (session %d) failed, rv = %s (%d)",
+			  vcm->my_pid, session_index,
+			  vppcom_retval_str (rv), rv);
+	}
+    }
   pool_put_index (vcm->sessions, session_index);
-  clib_spinlock_unlock (&vcm->sessions_lockp);
+done:
   return rv;
 }
 
@@ -1895,7 +1967,7 @@ vppcom_session_bind (uint32_t session_index, vppcom_endpt_t * ep)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, session_index);
       return rv;
     }
@@ -1927,7 +1999,7 @@ vppcom_session_listen (uint32_t listen_session_index, uint32_t q_len)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, listen_session_index);
       return rv;
     }
@@ -1957,13 +2029,13 @@ vppcom_session_listen (uint32_t listen_session_index, uint32_t q_len)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, listen_session_index);
       return rv;
     }
   listen_session->is_listen = 1;
-  clib_spinlock_unlock (&vcm->sessions_lockp);
   clib_fifo_validate (vcm->client_session_index_fifo, q_len);
+  clib_spinlock_unlock (&vcm->sessions_lockp);
 
   return VPPCOM_OK;
 }
@@ -1985,7 +2057,7 @@ vppcom_session_accept (uint32_t listen_session_index, vppcom_endpt_t * ep,
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, listen_session_index);
       return rv;
     }
@@ -2025,9 +2097,8 @@ vppcom_session_accept (uint32_t listen_session_index, vppcom_endpt_t * ep,
 	break;
     }
 
-  clib_fifo_sub1 (vcm->client_session_index_fifo, client_session_index);
-
   clib_spinlock_lock (&vcm->sessions_lockp);
+  clib_fifo_sub1 (vcm->client_session_index_fifo, client_session_index);
   rv = vppcom_session_at_index (client_session_index, &client_session);
   ASSERT (rv == VPPCOM_OK);
   ASSERT (client_session->is_ip4 == listen_session->is_ip4);
@@ -2062,7 +2133,7 @@ vppcom_session_connect (uint32_t session_index, vppcom_endpt_t * server_ep)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, session_index);
       return rv;
     }
@@ -2071,7 +2142,7 @@ vppcom_session_connect (uint32_t session_index, vppcom_endpt_t * server_ep)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] session, sid (%d) already connected!",
+	clib_warning ("[%d] session, sid (%u) already connected!",
 		      vcm->my_pid, session_index);
       return VPPCOM_OK;
     }
@@ -2115,7 +2186,6 @@ vppcom_session_read (uint32_t session_index, void *buf, int n)
   svm_fifo_t *rx_fifo;
   int n_read = 0;
   int rv;
-  int max_dequeue;
   char *fifo_str;
 
   ASSERT (buf);
@@ -2126,7 +2196,7 @@ vppcom_session_read (uint32_t session_index, void *buf, int n)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, session_index);
       return rv;
     }
@@ -2135,7 +2205,7 @@ vppcom_session_read (uint32_t session_index, void *buf, int n)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] sid (%d) has been closed by remote peer!",
+	clib_warning ("[%d] sid (%u) has been closed by remote peer!",
 		      vcm->my_pid, session_index);
       return VPPCOM_ECONNRESET;
     }
@@ -2144,12 +2214,19 @@ vppcom_session_read (uint32_t session_index, void *buf, int n)
 	     session->server_rx_fifo : session->server_tx_fifo);
   fifo_str = ((!session->is_cut_thru || session->is_server) ?
 	      "server_rx_fifo" : "server_tx_fifo");
-  clib_spinlock_unlock (&vcm->sessions_lockp);
 
-  max_dequeue = (int) svm_fifo_max_dequeue (rx_fifo);
-  n_read = svm_fifo_dequeue_nowait (rx_fifo, clib_min (n, max_dequeue), buf);
+  do
+    {
+      n_read = svm_fifo_dequeue_nowait (rx_fifo, n, buf);
+    }
+  while (!session->is_nonblocking && (n_read <= 0));
 
-  if (VPPCOM_DEBUG > 2)
+  if (n_read <= 0)
+    session->vep.et_mask |= EPOLLIN;
+
+  clib_spinlock_unlock (&vcm->sessions_lockp);
+
+  if ((VPPCOM_DEBUG > 2) && (n_read > 0))
     clib_warning ("[%d] sid %d, read %d bytes from %s (%p)", vcm->my_pid,
 		  session_index, n_read, fifo_str, rx_fifo);
 
@@ -2167,7 +2244,7 @@ vppcom_session_read_ready (session_t * session, u32 session_index)
   if (session->state == STATE_DISCONNECT)
     {
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] sid (%d) has been closed by remote peer!",
+	clib_warning ("[%d] sid (%u) has been closed by remote peer!",
 		      vcm->my_pid, session_index);
       return VPPCOM_ECONNRESET;
     }
@@ -2187,6 +2264,9 @@ vppcom_session_read_ready (session_t * session, u32 session_index)
 		  session_index,
 		  session->is_server ? "server_rx_fifo" : "server_tx_fifo",
 		  rx_fifo, ready);
+  if (ready == 0)
+    session->vep.et_mask |= EPOLLIN;
+
   return ready;
 }
 
@@ -2198,9 +2278,8 @@ vppcom_session_write (uint32_t session_index, void *buf, int n)
   svm_fifo_t *tx_fifo;
   unix_shared_memory_queue_t *q;
   session_fifo_event_t evt;
-  int rv;
+  int rv, n_write;
   char *fifo_str;
-  u8 is_nonblocking;
 
   ASSERT (buf);
 
@@ -2210,7 +2289,7 @@ vppcom_session_write (uint32_t session_index, void *buf, int n)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 		      vcm->my_pid, session_index);
       return rv;
     }
@@ -2219,7 +2298,7 @@ vppcom_session_write (uint32_t session_index, void *buf, int n)
     {
       clib_spinlock_unlock (&vcm->sessions_lockp);
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] sid (%d) has been closed by remote peer!",
+	clib_warning ("[%d] sid (%u) has been closed by remote peer!",
 		      vcm->my_pid, session_index);
       return VPPCOM_ECONNRESET;
     }
@@ -2228,18 +2307,14 @@ vppcom_session_write (uint32_t session_index, void *buf, int n)
 	     session->server_tx_fifo : session->server_rx_fifo);
   fifo_str = ((!session->is_cut_thru || session->is_server) ?
 	      "server_tx_fifo" : "server_rx_fifo");
-
-  is_nonblocking = session->is_nonblocking;
-  clib_spinlock_unlock (&vcm->sessions_lockp);
-
   do
     {
-      rv = svm_fifo_enqueue_nowait (tx_fifo, n, buf);
+      n_write = svm_fifo_enqueue_nowait (tx_fifo, n, buf);
     }
-  while (!is_nonblocking && (rv <= 0));
+  while (!session->is_nonblocking && (n_write <= 0));
 
   /* If event wasn't set, add one */
-  if (!session->is_cut_thru && (rv > 0) && svm_fifo_set_event (tx_fifo))
+  if (!session->is_cut_thru && (n_write > 0) && svm_fifo_set_event (tx_fifo))
     {
       int rval;
 
@@ -2248,28 +2323,30 @@ vppcom_session_write (uint32_t session_index, void *buf, int n)
       evt.event_type = FIFO_EVENT_APP_TX;
       evt.event_id = vcm->tx_event_id++;
 
-      clib_spinlock_lock (&vcm->sessions_lockp);
       rval = vppcom_session_at_index (session_index, &session);
       if (PREDICT_FALSE (rval))
 	{
 	  clib_spinlock_unlock (&vcm->sessions_lockp);
 	  if (VPPCOM_DEBUG > 1)
-	    clib_warning ("[%d] invalid session, sid (%d) has been closed!",
+	    clib_warning ("[%d] invalid session, sid (%u) has been closed!",
 			  vcm->my_pid, session_index);
 	  return rval;
 	}
       q = session->vpp_event_queue;
-      clib_spinlock_unlock (&vcm->sessions_lockp);
       ASSERT (q);
       unix_shared_memory_queue_add (q, (u8 *) & evt,
 				    0 /* do wait for mutex */ );
     }
 
+  if (n_write <= 0)
+    session->vep.et_mask |= EPOLLOUT;
+
+  clib_spinlock_unlock (&vcm->sessions_lockp);
+
   if (VPPCOM_DEBUG > 2)
     clib_warning ("[%d] sid %d, wrote %d bytes to %s (%p)", vcm->my_pid,
-		  session_index, rv, fifo_str, tx_fifo);
-
-  return rv;
+		  session_index, n_write, fifo_str, tx_fifo);
+  return n_write;
 }
 
 static inline int
@@ -2278,13 +2355,13 @@ vppcom_session_write_ready (session_t * session, u32 session_index)
   vppcom_main_t *vcm = &vppcom_main;
   svm_fifo_t *tx_fifo;
   char *fifo_str;
-  int rv;
+  int ready;
 
   /* Assumes caller has acquired spinlock: vcm->sessions_lockp */
   if (session->state == STATE_DISCONNECT)
     {
       if (VPPCOM_DEBUG > 0)
-	clib_warning ("[%d] sid (%d) has been closed by remote peer!",
+	clib_warning ("[%d] sid (%u) has been closed by remote peer!",
 		      vcm->my_pid, session_index);
       return VPPCOM_ECONNRESET;
     }
@@ -2294,12 +2371,15 @@ vppcom_session_write_ready (session_t * session, u32 session_index)
   fifo_str = ((!session->is_cut_thru || session->is_server) ?
 	      "server_tx_fifo" : "server_rx_fifo");
 
-  rv = svm_fifo_max_enqueue (tx_fifo);
+  ready = svm_fifo_max_enqueue (tx_fifo);
 
   if (VPPCOM_DEBUG > 3)
     clib_warning ("[%d] sid %d, peek %s (%p), ready = %d", vcm->my_pid,
-		  session_index, fifo_str, tx_fifo, rv);
-  return rv;
+		  session_index, fifo_str, tx_fifo, ready);
+  if (ready == 0)
+    session->vep.et_mask |= EPOLLOUT;
+
+  return ready;
 }
 
 int
@@ -2431,10 +2511,520 @@ select_done:
   return (bits_set);
 }
 
-/*
- * fd.io coding-style-patch-verification: ON
- *
- * Local Variables:
- * eval: (c-set-style "gnu")
- * End:
- */
+static inline void
+vep_verify_epoll_chain (u32 vep_idx)
+{
+  session_t *session;
+  vppcom_epoll_t *vep;
+  int rv;
+  u32 sid;
+
+  if (VPPCOM_DEBUG < 1)
+    return;
+
+  /* Assumes caller has acquired spinlock: vcm->sessions_lockp */
+  rv = vppcom_session_at_index (vep_idx, &session);
+  if (PREDICT_FALSE (rv))
+    {
+      clib_warning ("ERROR: Invalid vep_idx (%u)!", vep_idx);
+      goto done;
+    }
+  if (PREDICT_FALSE (!session->is_vep))
+    {
+      clib_warning ("ERROR: vep_idx (%u) is not a vep!", vep_idx);
+      goto done;
+    }
+  if (VPPCOM_DEBUG > 1)
+    clib_warning ("vep_idx (%u): Dumping epoll chain\n"
+		  "{\n"
+		  "   is_vep         = %u\n"
+		  "   is_vep_session = %u\n"
+		  "   wait_cont_idx  = 0x%x (%u)\n"
+		  "}\n",
+		  vep_idx, session->is_vep, session->is_vep_session,
+		  session->wait_cont_idx, session->wait_cont_idx);
+  do
+    {
+      vep = &session->vep;
+      if (session->is_vep_session)
+	{
+	  if (VPPCOM_DEBUG > 1)
+	    clib_warning ("vep_idx[%u]: sid 0x%x (%u)\n"
+			  "{\n"
+			  "   next_sid       = 0x%x (%u)\n"
+			  "   prev_sid       = 0x%x (%u)\n"
+			  "   vep_idx        = 0x%x (%u)\n"
+			  "   ev.events      = 0x%x\n"
+			  "   ev.data.u64    = 0x%llx\n"
+			  "   et_mask        = 0x%x\n"
+			  "}\n",
+			  vep_idx, sid, sid,
+			  vep->next_sid, vep->next_sid,
+			  vep->prev_sid, vep->prev_sid,
+			  vep->vep_idx, vep->vep_idx,
+			  vep->ev.events, vep->ev.data.u64, vep->et_mask);
+	}
+      sid = vep->next_sid;
+      if (sid != ~0)
+	{
+	  rv = vppcom_session_at_index (sid, &session);
+	  if (PREDICT_FALSE (rv))
+	    {
+	      clib_warning ("ERROR: Invalid sid (%u)!", sid);
+	      goto done;
+	    }
+	  if (PREDICT_FALSE (session->is_vep))
+	    clib_warning ("ERROR: sid (%u) is a vep!", vep_idx);
+	  else if (PREDICT_FALSE (!session->is_vep_session))
+	    {
+	      clib_warning ("ERROR: session (%u) is not a vep session!", sid);
+	      goto done;
+	    }
+	  if (PREDICT_FALSE (session->vep.vep_idx != vep_idx))
+	    clib_warning ("ERROR: session (%u) vep_idx (%u) != "
+			  "vep_idx (%u)!",
+			  sid, session->vep.vep_idx, vep_idx);
+	}
+    }
+  while (sid != ~0);
+
+done:
+  if (VPPCOM_DEBUG > 1)
+    clib_warning ("vep_idx (%u): Dump complete!", vep_idx);
+}
+
+int
+vppcom_epoll_create (void)
+{
+  vppcom_main_t *vcm = &vppcom_main;
+  session_t *vep_session;
+  u32 vep_idx;
+
+  clib_spinlock_lock (&vcm->sessions_lockp);
+  pool_get (vcm->sessions, vep_session);
+  memset (vep_session, 0, sizeof (*vep_session));
+  vep_idx = vep_session - vcm->sessions;
+
+  vep_session->is_vep = 1;
+  vep_session->vep.vep_idx = ~0;
+  vep_session->vep.next_sid = ~0;
+  vep_session->vep.prev_sid = ~0;
+  vep_session->wait_cont_idx = ~0;
+  clib_spinlock_unlock (&vcm->sessions_lockp);
+
+  if (VPPCOM_DEBUG > 0)
+    clib_warning ("Created vep_idx %u!", vep_idx);
+
+  return (vep_idx);
+}
+
+int
+vppcom_epoll_ctl (uint32_t vep_idx, int op, uint32_t session_index,
+		  struct epoll_event *event)
+{
+  vppcom_main_t *vcm = &vppcom_main;
+  session_t *vep_session;
+  session_t *session;
+  int rv;
+
+  if (vep_idx == session_index)
+    {
+      if (VPPCOM_DEBUG > 0)
+	clib_warning ("ERROR: vep_idx == session_index (%u)!", vep_idx);
+      return VPPCOM_EINVAL;
+    }
+
+  clib_spinlock_lock (&vcm->sessions_lockp);
+  rv = vppcom_session_at_index (vep_idx, &vep_session);
+  if (PREDICT_FALSE (rv))
+    {
+      if (VPPCOM_DEBUG > 0)
+	clib_warning ("ERROR: Invalid vep_idx (%u)!", vep_idx);
+      goto done;
+    }
+  if (PREDICT_FALSE (!vep_session->is_vep))
+    {
+      if (VPPCOM_DEBUG > 0)
+	clib_warning ("ERROR: vep_idx (%u) is not a vep!", vep_idx);
+      rv = VPPCOM_EINVAL;
+      goto done;
+    }
+
+  ASSERT (vep_session->vep.vep_idx == ~0);
+  ASSERT (vep_session->vep.prev_sid == ~0);
+
+  rv = vppcom_session_at_index (session_index, &session);
+  if (PREDICT_FALSE (rv))
+    {
+      if (VPPCOM_DEBUG > 0)
+	clib_warning ("ERROR: Invalid session_index (%u)!", session_index);
+      goto done;
+    }
+  if (PREDICT_FALSE (session->is_vep))
+    {
+      if (VPPCOM_DEBUG > 0)
+	clib_warning ("ERROR: session_index (%u) is a vep!", vep_idx);
+      rv = VPPCOM_EINVAL;
+      goto done;
+    }
+
+  switch (op)
+    {
+    case EPOLL_CTL_ADD:
+      if (PREDICT_FALSE (!event))
+	{
+	  clib_warning ("NULL pointer to epoll_event structure!");
+	  rv = VPPCOM_EINVAL;
+	  goto done;
+	}
+      if (vep_session->vep.next_sid != ~0)
+	{
+	  session_t *next_session;
+	  rv = vppcom_session_at_index (vep_session->vep.next_sid,
+					&next_session);
+	  if (PREDICT_FALSE (rv))
+	    {
+	      if (VPPCOM_DEBUG > 0)
+		clib_warning ("EPOLL_CTL_ADD: Invalid vep.next_sid (%u) on"
+			      " vep_idx (%u)!", vep_session->vep.next_sid,
+			      vep_idx);
+	      goto done;
+	    }
+	  ASSERT (next_session->vep.prev_sid == vep_idx);
+	  next_session->vep.prev_sid = session_index;
+	}
+      session->vep.next_sid = vep_session->vep.next_sid;
+      session->vep.prev_sid = vep_idx;
+      session->vep.vep_idx = vep_idx;
+      session->vep.et_mask = VEP_DEFAULT_ET_MASK;
+      session->vep.ev = *event;
+      session->is_vep_session = 1;
+      vep_session->vep.next_sid = session_index;
+      if (VPPCOM_DEBUG > 1)
+	clib_warning ("EPOLL_CTL_ADD: vep_idx %u, sid %u, events 0x%x,"
+		      " data 0x%llx!", vep_idx, session_index,
+		      event->events, event->data.u64);
+      break;
+
+    case EPOLL_CTL_MOD:
+      if (PREDICT_FALSE (!event))
+	{
+	  clib_warning ("NULL pointer to epoll_event structure!");
+	  rv = VPPCOM_EINVAL;
+	  goto done;
+	}
+      if (PREDICT_FALSE (!session->is_vep_session &&
+			 (session->vep.vep_idx != vep_idx)))
+	{
+	  if (VPPCOM_DEBUG > 0)
+	    {
+	      if (!session->is_vep_session)
+		clib_warning ("EPOLL_CTL_MOD: session (%u) is not "
+			      "a vep session!", session_index);
+	      else
+		clib_warning ("EPOLL_CTL_MOD: session (%u) vep_idx (%u) != "
+			      "vep_idx (%u)!", session_index,
+			      session->vep.vep_idx, vep_idx);
+	    }
+	  rv = VPPCOM_EINVAL;
+	  goto done;
+	}
+      session->vep.et_mask = VEP_DEFAULT_ET_MASK;
+      session->vep.ev = *event;
+      if (VPPCOM_DEBUG > 1)
+	clib_warning ("EPOLL_CTL_MOD: vep_idx %u, sid %u, events 0x%x,"
+		      " data 0x%llx!", vep_idx, session_index,
+		      event->events, event->data.u64);
+      break;
+
+    case EPOLL_CTL_DEL:
+      if (PREDICT_FALSE (!session->is_vep_session &&
+			 (session->vep.vep_idx != vep_idx)))
+	{
+	  if (VPPCOM_DEBUG > 0)
+	    {
+	      if (!session->is_vep_session)
+		clib_warning ("EPOLL_CTL_DEL: session (%u) is not "
+			      "a vep session!", session_index);
+	      else
+		clib_warning ("EPOLL_CTL_DEL: session (%u) vep_idx (%u) != "
+			      "vep_idx (%u)!", session_index,
+			      session->vep.vep_idx, vep_idx);
+	    }
+	  rv = VPPCOM_EINVAL;
+	  goto done;
+	}
+
+      vep_session->wait_cont_idx =
+	(vep_session->wait_cont_idx == session_index) ?
+	session->vep.next_sid : vep_session->wait_cont_idx;
+
+      if (session->vep.prev_sid == vep_idx)
+	vep_session->vep.next_sid = session->vep.next_sid;
+      else
+	{
+	  session_t *prev_session;
+	  rv = vppcom_session_at_index (session->vep.prev_sid, &prev_session);
+	  if (PREDICT_FALSE (rv))
+	    {
+	      if (VPPCOM_DEBUG > 0)
+		clib_warning ("EPOLL_CTL_DEL: Invalid vep.prev_sid (%u) on"
+			      " sid (%u)!", session->vep.prev_sid,
+			      session_index);
+	      goto done;
+	    }
+	  ASSERT (prev_session->vep.next_sid == session_index);
+	  prev_session->vep.next_sid = session->vep.next_sid;
+	}
+      if (session->vep.next_sid != ~0)
+	{
+	  session_t *next_session;
+	  rv = vppcom_session_at_index (session->vep.next_sid, &next_session);
+	  if (PREDICT_FALSE (rv))
+	    {
+	      if (VPPCOM_DEBUG > 0)
+		clib_warning ("EPOLL_CTL_DEL: Invalid vep.next_sid (%u) on"
+			      " sid (%u)!", session->vep.next_sid,
+			      session_index);
+	      goto done;
+	    }
+	  ASSERT (next_session->vep.prev_sid == session_index);
+	  next_session->vep.prev_sid = session->vep.prev_sid;
+	}
+
+      memset (&session->vep, 0, sizeof (session->vep));
+      session->vep.next_sid = ~0;
+      session->vep.prev_sid = ~0;
+      session->vep.vep_idx = ~0;
+      session->is_vep_session = 0;
+      if (VPPCOM_DEBUG > 1)
+	clib_warning ("EPOLL_CTL_DEL: vep_idx %u, sid %u!", vep_idx,
+		      session_index);
+      break;
+
+    default:
+      clib_warning ("Invalid operation (%d)!", op);
+      rv = VPPCOM_EINVAL;
+    }
+
+  vep_verify_epoll_chain (vep_idx);
+
+done:
+  clib_spinlock_unlock (&vcm->sessions_lockp);
+  return rv;
+}
+
+#define VCL_LOCK_AND_GET_SESSION(I, S)                  \
+do {                                                    \
+  vppcom_main_t *vcm = &vppcom_main;                    \
+                                                        \
+  clib_spinlock_lock (&vcm->sessions_lockp);            \
+  rv = vppcom_session_at_index (I, S);                  \
+  if (PREDICT_FALSE (rv))                               \
+    {                                                   \
+      clib_spinlock_unlock (&vcm->sessions_lockp);      \
+                                                        \
+      if (VPPCOM_DEBUG > 0)                             \
+        clib_warning ("ERROR: Invalid ##I (%u)!", I);   \
+                                                        \
+      goto done;                                        \
+    }                                                   \
+} while (0)
+
+int
+vppcom_epoll_wait (uint32_t vep_idx, struct epoll_event *events,
+		   int maxevents, double wait_for_time)
+{
+  vppcom_main_t *vcm = &vppcom_main;
+  session_t *vep_session;
+  int rv;
+  f64 timeout = clib_time_now (&vcm->clib_time) + wait_for_time;
+  int num_ev = 0;
+  u32 vep_next_sid, wait_cont_idx;
+  u8 is_vep;
+
+  if (PREDICT_FALSE (maxevents <= 0))
+    {
+      if (VPPCOM_DEBUG > 0)
+	clib_warning ("ERROR: Invalid maxevents (%d)!", maxevents);
+      return VPPCOM_EINVAL;
+    }
+  if (PREDICT_FALSE (wait_for_time < 0))
+    {
+      if (VPPCOM_DEBUG > 0)
+	clib_warning ("ERROR: Invalid wait_for_time (%f)!", wait_for_time);
+      return VPPCOM_EINVAL;
+    }
+  memset (events, 0, sizeof (*events) * maxevents);
+
+  VCL_LOCK_AND_GET_SESSION (vep_idx, &vep_session);
+  vep_next_sid = vep_session->vep.next_sid;
+  is_vep = vep_session->is_vep;
+  wait_cont_idx = vep_session->wait_cont_idx;
+  clib_spinlock_unlock (&vcm->sessions_lockp);
+
+  if (PREDICT_FALSE (!is_vep))
+    {
+      if (VPPCOM_DEBUG > 0)
+	clib_warning ("ERROR: vep_idx (%u) is not a vep!", vep_idx);
+      rv = VPPCOM_EINVAL;
+      goto done;
+    }
+  if ((VPPCOM_DEBUG > 0) && (PREDICT_FALSE (vep_next_sid == ~0)))
+    {
+      clib_warning ("WARNING: vep_idx (%u) is empty!", vep_idx);
+      goto done;
+    }
+
+  do
+    {
+      u32 sid;
+      u32 next_sid = ~0;
+      session_t *session;
+
+      for (sid = (wait_cont_idx == ~0) ? vep_next_sid : wait_cont_idx;
+	   sid != ~0; sid = next_sid)
+	{
+	  u32 session_events, et_mask, clear_et_mask, session_vep_idx;
+	  u8 add_event, is_vep_session;
+	  int ready;
+	  u64 session_ev_data;
+
+	  VCL_LOCK_AND_GET_SESSION (sid, &session);
+	  next_sid = session->vep.next_sid;
+	  session_events = session->vep.ev.events;
+	  et_mask = session->vep.et_mask;
+	  is_vep = session->is_vep;
+	  is_vep_session = session->is_vep_session;
+	  session_vep_idx = session->vep.vep_idx;
+	  session_ev_data = session->vep.ev.data.u64;
+	  clib_spinlock_unlock (&vcm->sessions_lockp);
+
+	  if (PREDICT_FALSE (is_vep))
+	    {
+	      if (VPPCOM_DEBUG > 0)
+		clib_warning ("ERROR: sid (%u) is a vep!", vep_idx);
+	      rv = VPPCOM_EINVAL;
+	      goto done;
+	    }
+	  if (PREDICT_FALSE (!is_vep_session))
+	    {
+	      if (VPPCOM_DEBUG > 0)
+		clib_warning ("EPOLL_CTL_MOD: session (%u) is not "
+			      "a vep session!", sid);
+	      rv = VPPCOM_EINVAL;
+	      goto done;
+	    }
+	  if (PREDICT_FALSE (session_vep_idx != vep_idx))
+	    {
+	      clib_warning ("EPOLL_CTL_MOD: session (%u) "
+			    "vep_idx (%u) != vep_idx (%u)!",
+			    sid, session->vep.vep_idx, vep_idx);
+	      rv = VPPCOM_EINVAL;
+	      goto done;
+	    }
+
+	  add_event = clear_et_mask = 0;
+
+	  if ((EPOLLIN & session_events) && (EPOLLIN & et_mask))
+	    {
+	      VCL_LOCK_AND_GET_SESSION (sid, &session);
+	      ready = vppcom_session_read_ready (session, sid);
+	      clib_spinlock_unlock (&vcm->sessions_lockp);
+	      if (ready > 0)
+		{
+		  add_event = 1;
+		  events[num_ev].events |= EPOLLIN;
+		  if (EPOLLET & session_events)
+		    clear_et_mask |= EPOLLIN;
+		}
+	      else if (ready < 0)
+		{
+		  add_event = 1;
+		  switch (ready)
+		    {
+		    case VPPCOM_ECONNRESET:
+		      events[num_ev].events |= EPOLLHUP | EPOLLRDHUP;
+		      break;
+
+		    default:
+		      events[num_ev].events |= EPOLLERR;
+		      break;
+		    }
+		}
+	    }
+
+	  if ((EPOLLOUT & session_events) && (EPOLLOUT & et_mask))
+	    {
+	      VCL_LOCK_AND_GET_SESSION (sid, &session);
+	      ready = vppcom_session_write_ready (session, sid);
+	      clib_spinlock_unlock (&vcm->sessions_lockp);
+	      if (ready > 0)
+		{
+		  add_event = 1;
+		  events[num_ev].events |= EPOLLOUT;
+		  if (EPOLLET & session_events)
+		    clear_et_mask |= EPOLLOUT;
+		}
+	      else if (ready < 0)
+		{
+		  add_event = 1;
+		  switch (ready)
+		    {
+		    case VPPCOM_ECONNRESET:
+		      events[num_ev].events |= EPOLLHUP;
+		      break;
+
+		    default:
+		      events[num_ev].events |= EPOLLERR;
+		      break;
+		    }
+		}
+	    }
+
+	  if (add_event)
+	    {
+	      events[num_ev].data.u64 = session_ev_data;
+	      if (EPOLLONESHOT & session_events)
+		{
+		  VCL_LOCK_AND_GET_SESSION (sid, &session);
+		  session->vep.ev.events = 0;
+		  clib_spinlock_unlock (&vcm->sessions_lockp);
+		}
+	      num_ev++;
+	      if (num_ev == maxevents)
+		{
+		  VCL_LOCK_AND_GET_SESSION (vep_idx, &vep_session);
+		  vep_session->wait_cont_idx = next_sid;
+		  clib_spinlock_unlock (&vcm->sessions_lockp);
+		  goto done;
+		}
+	    }
+	  if (wait_cont_idx != ~0)
+	    {
+	      if (next_sid == ~0)
+		next_sid = vep_next_sid;
+	      else if (next_sid == wait_cont_idx)
+		next_sid = ~0;
+	    }
+	}
+    }
+  while ((num_ev == 0) && (clib_time_now (&vcm->clib_time) <= timeout));
+
+  if (wait_cont_idx != ~0)
+    {
+      VCL_LOCK_AND_GET_SESSION (vep_idx, &vep_session);
+      vep_session->wait_cont_idx = ~0;
+      clib_spinlock_unlock (&vcm->sessions_lockp);
+    }
+done:
+  return (rv != VPPCOM_OK) ? rv : num_ev;
+}
+
+  /*
+   * fd.io coding-style-patch-verification: ON
+   *
+   * Local Variables:
+   * eval: (c-set-style "gnu")
+   * End:
+   */
diff --git a/src/uri/vppcom.h b/src/uri/vppcom.h
index 4b048e039ec..b7c802897d9 100644
--- a/src/uri/vppcom.h
+++ b/src/uri/vppcom.h
@@ -18,6 +18,7 @@
 
 #include <netdb.h>
 #include <errno.h>
+#include <sys/epoll.h>
 
 /*
  * VPPCOM Public API Definitions, Enums, and Data Structures
@@ -141,6 +142,13 @@ extern int vppcom_select (unsigned long n_bits,
 			  unsigned long *write_map,
 			  unsigned long *except_map, double wait_for_time);
 
+extern int vppcom_epoll_create (void);
+extern int vppcom_epoll_ctl (uint32_t vep_idx, int op,
+			     uint32_t session_index,
+			     struct epoll_event *event);
+extern int vppcom_epoll_wait (uint32_t vep_idx, struct epoll_event *events,
+			      int maxevents, double wait_for_time);
+
 #endif /* included_vppcom_h */
 
 /*