netfront: preserve configuration across migrations

Try to preserve the xn configuration when migrating. This is not always
possible since the backend might not have the same set of options
available, in which case we will try to preserve as many as possible.

MFC after:    2 weeks
PR:           183139
Reported by:  mcdouga9@egr.msu.edu
Sponsored by: Citrix Systems R&D

1 files changed, 24 insertions, 5 deletions

diff --git a/sys/dev/xen/netfront/netfront.c b/sys/dev/xen/netfront/netfront.c
index 317a339..3eac25d 100644
--- a/sys/dev/xen/netfront/netfront.c
+++ b/sys/dev/xen/netfront/netfront.c
@@ -285,6 +285,8 @@ struct netfront_info {
 	multicall_entry_t	rx_mcl[NET_RX_RING_SIZE+1];
 	mmu_update_t		rx_mmu[NET_RX_RING_SIZE];
 	struct ifmedia		sc_media;
+
+	bool			xn_resume;
 };
 
 #define rx_mbufs xn_cdata.xn_rx_chain
@@ -500,6 +502,7 @@ netfront_resume(device_t dev)
 {
 	struct netfront_info *info = device_get_softc(dev);
 
+	info->xn_resume = true;
 	netif_disconnect_backend(info);
 	return (0);
 }
@@ -1982,18 +1985,33 @@ xn_query_features(struct netfront_info *np)
 static int
 xn_configure_features(struct netfront_info *np)
 {
-	int err;
+	int err, cap_enabled;
 
 	err = 0;
+
+	if (np->xn_resume &&
+	    ((np->xn_ifp->if_capenable & np->xn_ifp->if_capabilities)
+	    == np->xn_ifp->if_capenable)) {
+		/* Current options are available, no need to do anything. */
+		return (0);
+	}
+
+	/* Try to preserve as many options as possible. */
+	if (np->xn_resume)
+		cap_enabled = np->xn_ifp->if_capenable;
+	else
+		cap_enabled = UINT_MAX;
+
 #if __FreeBSD_version >= 700000 && (defined(INET) || defined(INET6))
-	if ((np->xn_ifp->if_capenable & IFCAP_LRO) != 0)
+	if ((np->xn_ifp->if_capenable & IFCAP_LRO) == (cap_enabled & IFCAP_LRO))
 		tcp_lro_free(&np->xn_lro);
 #endif
     	np->xn_ifp->if_capenable =
-	    np->xn_ifp->if_capabilities & ~(IFCAP_LRO|IFCAP_TSO4);
+	    np->xn_ifp->if_capabilities & ~(IFCAP_LRO|IFCAP_TSO4) & cap_enabled;
 	np->xn_ifp->if_hwassist &= ~CSUM_TSO;
 #if __FreeBSD_version >= 700000 && (defined(INET) || defined(INET6))
-	if (xn_enable_lro && (np->xn_ifp->if_capabilities & IFCAP_LRO) != 0) {
+	if (xn_enable_lro && (np->xn_ifp->if_capabilities & IFCAP_LRO) ==
+	    (cap_enabled & IFCAP_LRO)) {
 		err = tcp_lro_init(&np->xn_lro);
 		if (err) {
 			device_printf(np->xbdev, "LRO initialization failed\n");
@@ -2002,7 +2020,8 @@ xn_configure_features(struct netfront_info *np)
 			np->xn_ifp->if_capenable |= IFCAP_LRO;
 		}
 	}
-	if ((np->xn_ifp->if_capabilities & IFCAP_TSO4) != 0) {
+	if ((np->xn_ifp->if_capabilities & IFCAP_TSO4) ==
+	    (cap_enabled & IFCAP_TSO4)) {
 		np->xn_ifp->if_capenable |= IFCAP_TSO4;
 		np->xn_ifp->if_hwassist |= CSUM_TSO;
 	}