PPP: remove unused and confusing return values other than ERR_OK for ppp_connect and ppp_listen

User should not use ppp_connect or ppp_listen return value to retry
later, it must wait for the callback to be called. This is primarily
done this way to have a consistent behavior with and without the
holdoff feature.

Remove returned error value from PPP link level API connect and listen
callbacks because we are not using them anymore, then make ppp_connect
or ppp_listen to always return ERR_OK, thus we are not breaking the PPP
user API.

We don't need the return code here, all PPP link level drivers can't
fail at all (e.g. PPPoS) or retry if necessary (PPPoE and PPPoL2TP).

(cherry picked from commit e16d10ade6204a2f896eb872fb5075bec8e5164f)

src/include/netif/ppp/ppp_impl.h

@@ -138,10 +138,10 @@
  */
 struct link_callbacks {
   /* Start a connection (e.g. Initiate discovery phase) */
-  err_t (*connect) (ppp_pcb *pcb, void *ctx);
+  void (*connect) (ppp_pcb *pcb, void *ctx);
 #if PPP_SERVER
   /* Listen for an incoming connection (Passive mode) */
-  err_t (*listen) (ppp_pcb *pcb, void *ctx);
+  void (*listen) (ppp_pcb *pcb, void *ctx);
 #endif /* PPP_SERVER */
   /* End a connection (i.e. initiate disconnect phase) */
   void (*disconnect) (ppp_pcb *pcb, void *ctx);

src/netif/ppp/ppp.c

@@ -275,8 +275,8 @@ err_t ppp_connect(ppp_pcb *pcb, u16_t holdoff) {
   PPPDEBUG(LOG_DEBUG, ("ppp_connect[%d]: holdoff=%d\n", pcb->netif->num, holdoff));
 
   if (holdoff == 0) {
-    new_phase(pcb, PPP_PHASE_INITIALIZE);
-    return pcb->link_cb->connect(pcb, pcb->link_ctx_cb);
+    ppp_do_connect(pcb);
+    return ERR_OK;
   }
 
   new_phase(pcb, PPP_PHASE_HOLDOFF);
@@ -302,7 +302,8 @@ err_t ppp_listen(ppp_pcb *pcb) {
 
   if (pcb->link_cb->listen) {
     new_phase(pcb, PPP_PHASE_INITIALIZE);
-    return pcb->link_cb->listen(pcb, pcb->link_ctx_cb);
+    pcb->link_cb->listen(pcb, pcb->link_ctx_cb);
+    return ERR_OK;
   }
   return ERR_IF;
 }

src/netif/ppp/pppoe.c

@@ -119,7 +119,7 @@ LWIP_MEMPOOL_DECLARE(PPPOE_IF, MEMP_NUM_PPPOE_INTERFACES, sizeof(struct pppoe_so
 /* callbacks called from PPP core */
 static err_t pppoe_write(ppp_pcb *ppp, void *ctx, struct pbuf *p);
 static err_t pppoe_netif_output(ppp_pcb *ppp, void *ctx, struct pbuf *p, u_short protocol);
-static err_t pppoe_connect(ppp_pcb *ppp, void *ctx);
+static void pppoe_connect(ppp_pcb *ppp, void *ctx);
 static void pppoe_disconnect(ppp_pcb *ppp, void *ctx);
 static err_t pppoe_destroy(ppp_pcb *ppp, void *ctx);
 
@@ -879,7 +879,7 @@ pppoe_timeout(void *arg)
 }
 
 /* Start a connection (i.e. initiate discovery phase) */
-static err_t
+static void
 pppoe_connect(ppp_pcb *ppp, void *ctx)
 {
   err_t err;
@@ -934,7 +934,6 @@ pppoe_connect(ppp_pcb *ppp, void *ctx)
     PPPDEBUG(LOG_DEBUG, ("pppoe: %c%c%"U16_F": failed to send PADI, error=%d\n", sc->sc_ethif->name[0], sc->sc_ethif->name[1], sc->sc_ethif->num, err));
   }
   sys_timeout(PPPOE_DISC_TIMEOUT, pppoe_timeout, sc);
-  return err;
 }
 
 /* disconnect */

src/netif/ppp/pppol2tp.c

@@ -73,7 +73,7 @@ LWIP_MEMPOOL_DECLARE(PPPOL2TP_PCB, MEMP_NUM_PPPOL2TP_INTERFACES, sizeof(pppol2tp
 static err_t pppol2tp_write(ppp_pcb *ppp, void *ctx, struct pbuf *p);
 static err_t pppol2tp_netif_output(ppp_pcb *ppp, void *ctx, struct pbuf *p, u_short protocol);
 static err_t pppol2tp_destroy(ppp_pcb *ppp, void *ctx);    /* Destroy a L2TP control block */
-static err_t pppol2tp_connect(ppp_pcb *ppp, void *ctx);    /* Be a LAC, connect to a LNS. */
+static void pppol2tp_connect(ppp_pcb *ppp, void *ctx);    /* Be a LAC, connect to a LNS. */
 static void pppol2tp_disconnect(ppp_pcb *ppp, void *ctx);  /* Disconnect */
 
  /* Prototypes for procedures local to this file. */
@@ -255,7 +255,7 @@ static err_t pppol2tp_destroy(ppp_pcb *ppp, void *ctx) {
 }
 
 /* Be a LAC, connect to a LNS. */
-static err_t pppol2tp_connect(ppp_pcb *ppp, void *ctx) {
+static void pppol2tp_connect(ppp_pcb *ppp, void *ctx) {
   err_t err;
   pppol2tp_pcb *l2tp = (pppol2tp_pcb *)ctx;
   lcp_options *lcp_wo;
@@ -326,7 +326,6 @@ static err_t pppol2tp_connect(ppp_pcb *ppp, void *ctx) {
     PPPDEBUG(LOG_DEBUG, ("pppol2tp: failed to send SCCRQ, error=%d\n", err));
   }
   sys_timeout(PPPOL2TP_CONTROL_TIMEOUT, pppol2tp_timeout, l2tp);
-  return err;
 }
 
 /* Disconnect */

src/netif/ppp/pppos.c

@@ -57,9 +57,9 @@ LWIP_MEMPOOL_DECLARE(PPPOS_PCB, MEMP_NUM_PPPOS_INTERFACES, sizeof(pppos_pcb), "P
 /* callbacks called from PPP core */
 static err_t pppos_write(ppp_pcb *ppp, void *ctx, struct pbuf *p);
 static err_t pppos_netif_output(ppp_pcb *ppp, void *ctx, struct pbuf *pb, u16_t protocol);
-static err_t pppos_connect(ppp_pcb *ppp, void *ctx);
+static void pppos_connect(ppp_pcb *ppp, void *ctx);
 #if PPP_SERVER
-static err_t pppos_listen(ppp_pcb *ppp, void *ctx);
+static void pppos_listen(ppp_pcb *ppp, void *ctx);
 #endif /* PPP_SERVER */
 static void pppos_disconnect(ppp_pcb *ppp, void *ctx);
 static err_t pppos_destroy(ppp_pcb *ppp, void *ctx);
@@ -298,7 +298,7 @@ pppos_netif_output(ppp_pcb *ppp, void *ctx, struct pbuf *pb, u16_t protocol)
   return err;
 }
 
-static err_t
+static void
 pppos_connect(ppp_pcb *ppp, void *ctx)
 {
   pppos_pcb *pppos = (pppos_pcb *)ctx;
@@ -327,11 +327,10 @@ pppos_connect(ppp_pcb *ppp, void *ctx)
    */
   PPPDEBUG(LOG_INFO, ("pppos_connect: unit %d: connecting\n", ppp->netif->num));
   ppp_start(ppp); /* notify upper layers */
-  return ERR_OK;
 }
 
 #if PPP_SERVER
-static err_t
+static void
 pppos_listen(ppp_pcb *ppp, void *ctx)
 {
   pppos_pcb *pppos = (pppos_pcb *)ctx;
@@ -360,7 +359,6 @@ pppos_listen(ppp_pcb *ppp, void *ctx)
    */
   PPPDEBUG(LOG_INFO, ("pppos_listen: unit %d: listening\n", ppp->netif->num));
   ppp_start(ppp); /* notify upper layers */
-  return ERR_OK;
 }
 #endif /* PPP_SERVER */