Disable checksum processing in LibAlias, when it works as a

kernel module. LibAlias is not aware about checksum offloading,
so the caller should provide checksum calculation. (The only
current consumer is ng_nat(4)). When TCP packet internals has
been changed and it requires checksum recalculation, a cookie
is set in th_x2 field of TCP packet, to inform caller that it
needs to recalculate checksum. This ugly hack would be removed
when LibAlias is made more kernel friendly.

Incremental checksum updates are left as is, since they don't
conflict with offloading.

Approved by:	re (scottl)

sys/netinet/libalias/alias_ftp.c

@@ -677,7 +677,11 @@ NewFtpMessage(struct libalias *la, struct ip *pip,
 
 /* Compute TCP checksum for revised packet */
 		tc->th_sum = 0;
+#ifdef _KERNEL
+		tc->th_x2 = 1;
+#else
 		tc->th_sum = TcpChecksum(pip);
+#endif
 	} else {
 #ifdef LIBALIAS_DEBUG
 		fprintf(stderr,

sys/netinet/libalias/alias_irc.c

@@ -374,7 +374,11 @@ lPACKET_DONE:
 
 		/* Compute TCP checksum for revised packet */
 		tc->th_sum = 0;
+#ifdef _KERNEL
+		tc->th_x2 = 1;
+#else
 		tc->th_sum = TcpChecksum(pip);
+#endif
 		return;
 	}
 }

sys/netinet/libalias/alias_local.h

@@ -178,9 +178,18 @@ struct libalias {
 
 /* Prototypes */
 
-/* General utilities */
+/*
+ * We do not calculate TCP checksums when libalias is a kernel
+ * module, since it has no idea about checksum offloading.
+ * If TCP data has changed, then we just set checksum to zero,
+ * and caller must recalculate it himself.
+ * In case if libalias will edit UDP data, the same approach
+ * should be used.
+ */
+#ifndef _KERNEL
 u_short		IpChecksum(struct ip *_pip);
 u_short		TcpChecksum(struct ip *_pip);
+#endif
 void
 DifferentialChecksum(u_short * _cksum, void * _new, void * _old, int _n);
 

sys/netinet/libalias/alias_proxy.c

@@ -474,7 +474,11 @@ ProxyEncodeTcpStream(struct alias_link *lnk,
    already changed. */
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
+#endif
 }
 
 static void

sys/netinet/libalias/alias_skinny.c

@@ -150,7 +150,11 @@ alias_skinny_reg_msg(struct RegisterMessage *reg_msg, struct ip *pip,
 	reg_msg->ipAddr = (u_int32_t) GetAliasAddress(lnk).s_addr;
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
+#endif
 
 	return (0);
 }
@@ -189,8 +193,11 @@ alias_skinny_port_msg(struct IpPortMessage *port_msg, struct ip *pip,
 	port_msg->stationIpPort = (u_int32_t) ntohs(GetAliasPort(lnk));
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
-
+#endif
 	return (0);
 }
 
@@ -218,8 +225,11 @@ alias_skinny_opnrcvch_ack(struct libalias *la, struct OpenReceiveChannelAck *opn
 	opnrcvch_ack->port = (u_int32_t) ntohs(GetAliasPort(opnrcv_lnk));
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
-
+#endif
 	return (0);
 }
 

sys/netinet/libalias/alias_smedia.c

@@ -331,8 +331,11 @@ alias_rtsp_out(struct libalias *la, struct ip *pip,
 	pip->ip_len = new_len;
 
 	tc->th_sum = 0;
+#ifdef _KERNEL
+	tc->th_x2 = 1;
+#else
 	tc->th_sum = TcpChecksum(pip);
-
+#endif
 	return (0);
 }
 
@@ -376,7 +379,11 @@ alias_pna_out(struct libalias *la, struct ip *pip,
 
 				/* Compute TCP checksum for revised packet */
 				tc->th_sum = 0;
+#ifdef _KERNEL
+				tc->th_x2 = 1;
+#else
 				tc->th_sum = TcpChecksum(pip);
+#endif
 			}
 		}
 		work += ntohs(msg_len);

sys/netinet/libalias/alias_util.c

@@ -43,13 +43,6 @@ __FBSDID("$FreeBSD$");
 	 Added differential checksum update function.
 */
 
-/*
-Note: the checksum routines assume that the actual checksum word has
-been zeroed out.  If the checksum word is filled with the proper value,
-then these routines will give a result of zero (useful for testing
-purposes);
-*/
-
 #ifdef _KERNEL
 #include <sys/param.h>
 #else
@@ -70,6 +63,12 @@ purposes);
 #include "alias_local.h"
 #endif
 
+/*
+ * Note: the checksum routines assume that the actual checksum word has
+ * been zeroed out.  If the checksum word is filled with the proper value,
+ * then these routines will give a result of zero (useful for testing
+ * purposes);
+ */
 u_short
 LibAliasInternetChecksum(struct libalias *la __unused, u_short * ptr,
 	int nbytes)
@@ -92,6 +91,7 @@ LibAliasInternetChecksum(struct libalias *la __unused, u_short * ptr,
 	return (~sum);
 }
 
+#ifndef	_KERNEL
 u_short
 IpChecksum(struct ip *pip)
 {
@@ -144,7 +144,7 @@ TcpChecksum(struct ip *pip)
 /* Return checksum */
 	return ((u_short) ~ sum);
 }
-
+#endif	/* not _KERNEL */
 
 void
 DifferentialChecksum(u_short * cksum, void *newp, void *oldp, int n)