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Date:      Sun, 24 Feb 2019 22:49:56 +0000 (UTC)
From:      "Bjoern A. Zeeb" <bz@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r344504 - head/sys/netinet
Message-ID:  <201902242249.x1OMnuqN094107@repo.freebsd.org>
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Author: bz
Date: Sun Feb 24 22:49:56 2019
New Revision: 344504
URL: https://svnweb.freebsd.org/changeset/base/344504

Log:
  Make arp code return (more) errors.
  
  arprequest() is a void function and in case of error we simply
  return without any feedback. In case of any local operation
  or *if_output() failing no feedback is send up the stack for the
  packet which triggered the arp request to be sent.
  arpresolve_full() has three pre-canned possible errors returned
  (if we have not yet sent enough arp requests or if we tried
  often enough without success) otherwise "no error" is returned.
  
  Make arprequest() an "internal" function arprequest_internal() which
  does return a possible error to the caller. Preserve arprequest()
  as a void wrapper function for external consumers.
  In arpresolve_full() add an extra error checking. Use the
  arprequest_internal() function and only return an error if non
  of the three ones (mentioend above) are already set.
  
  This will return possible errors all the way up the stack and
  allows functions and programs to react on the send errors rather
  than leaving them in the dark. Also they might get more detailed
  feedback of why packets cannot be sent and they will receive it
  quicker.
  
  Reviewed by:		karels, hselasky
  Differential Revision:	https://reviews.freebsd.org/D18904

Modified:
  head/sys/netinet/if_ether.c

Modified: head/sys/netinet/if_ether.c
==============================================================================
--- head/sys/netinet/if_ether.c	Sun Feb 24 21:22:16 2019	(r344503)
+++ head/sys/netinet/if_ether.c	Sun Feb 24 22:49:56 2019	(r344504)
@@ -341,8 +341,8 @@ arp_fillheader(struct ifnet *ifp, struct arphdr *ah, i
  *	- arp header target ip address
  *	- arp header source ethernet address
  */
-void
-arprequest(struct ifnet *ifp, const struct in_addr *sip,
+static int
+arprequest_internal(struct ifnet *ifp, const struct in_addr *sip,
     const struct in_addr *tip, u_char *enaddr)
 {
 	struct mbuf *m;
@@ -383,14 +383,14 @@ arprequest(struct ifnet *ifp, const struct in_addr *si
 		NET_EPOCH_EXIT(et);
 		if (sip == NULL) {
 			printf("%s: cannot find matching address\n", __func__);
-			return;
+			return (EADDRNOTAVAIL);
 		}
 	}
 	if (enaddr == NULL)
 		enaddr = carpaddr ? carpaddr : (u_char *)IF_LLADDR(ifp);
 
 	if ((m = m_gethdr(M_NOWAIT, MT_DATA)) == NULL)
-		return;
+		return (ENOMEM);
 	m->m_len = sizeof(*ah) + 2 * sizeof(struct in_addr) +
 		2 * ifp->if_addrlen;
 	m->m_pkthdr.len = m->m_len;
@@ -417,7 +417,7 @@ arprequest(struct ifnet *ifp, const struct in_addr *si
 	if (error != 0 && error != EAFNOSUPPORT) {
 		ARP_LOG(LOG_ERR, "Failed to calculate ARP header on %s: %d\n",
 		    if_name(ifp), error);
-		return;
+		return (error);
 	}
 
 	ro.ro_prepend = linkhdr;
@@ -426,11 +426,22 @@ arprequest(struct ifnet *ifp, const struct in_addr *si
 
 	m->m_flags |= M_BCAST;
 	m_clrprotoflags(m);	/* Avoid confusing lower layers. */
-	(*ifp->if_output)(ifp, m, &sa, &ro);
+	error = (*ifp->if_output)(ifp, m, &sa, &ro);
 	ARPSTAT_INC(txrequests);
+	if (error)
+		ARP_LOG(LOG_DEBUG, "Failed to send ARP packet on %s: %d\n",
+		    if_name(ifp), error);
+	return (error);
 }
 
+void
+arprequest(struct ifnet *ifp, const struct in_addr *sip,
+    const struct in_addr *tip, u_char *enaddr)
+{
 
+	(void) arprequest_internal(ifp, sip, tip, enaddr);
+}
+
 /*
  * Resolve an IP address into an ethernet address - heavy version.
  * Used internally by arpresolve().
@@ -557,7 +568,7 @@ arpresolve_full(struct ifnet *ifp, int is_gw, int flag
 		error = is_gw != 0 ? EHOSTUNREACH : EHOSTDOWN;
 
 	if (renew) {
-		int canceled;
+		int canceled, e;
 
 		LLE_ADDREF(la);
 		la->la_expire = time_uptime;
@@ -567,7 +578,13 @@ arpresolve_full(struct ifnet *ifp, int is_gw, int flag
 			LLE_REMREF(la);
 		la->la_asked++;
 		LLE_WUNLOCK(la);
-		arprequest(ifp, NULL, &SIN(dst)->sin_addr, NULL);
+		e = arprequest_internal(ifp, NULL, &SIN(dst)->sin_addr, NULL);
+		/*
+		 * Only overwrite 'error' in case of error; in case of success
+		 * the proper return value was already set above.
+		 */
+		if (e != 0)
+			return (e);
 		return (error);
 	}

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