[IPX]: Annotate and fix IPX checksum

[uclinux-h8/linux.git] / net / ipx / af_ipx.c

diff --git a/net/ipx/af_ipx.c b/net/ipx/af_ipx.c
index c272a38..76c6615 100644 (file)
--- a/net/ipx/af_ipx.c
+++ b/net/ipx/af_ipx.c
@@ -1234,27 +1234,27 @@ static int ipxitf_ioctl(unsigned int cmd, void __user *arg)
 /* Note: We assume ipx_tctrl==0 and htons(length)==ipx_pktsize */
 /* This functions should *not* mess with packet contents */
 
-__u16 ipx_cksum(struct ipxhdr *packet, int length) 
+__be16 ipx_cksum(struct ipxhdr *packet, int length)
 {
        /* 
         *      NOTE: sum is a net byte order quantity, which optimizes the 
         *      loop. This only works on big and little endian machines. (I
         *      don't know of a machine that isn't.)
         */
-       /* start at ipx_dest - We skip the checksum field and start with
-        * ipx_type before the loop, not considering ipx_tctrl in the calc */
-       __u16 *p = (__u16 *)&packet->ipx_dest;
-       __u32 i = (length >> 1) - 1; /* Number of complete words */
-       __u32 sum = packet->ipx_type << sizeof(packet->ipx_tctrl); 
-
-       /* Loop through all complete words except the checksum field,
-        * ipx_type (accounted above) and ipx_tctrl (not used in the cksum) */
-       while (--i)
+       /* handle the first 3 words separately; checksum should be skipped
+        * and ipx_tctrl masked out */
+       __u16 *p = (__u16 *)packet;
+       __u32 sum = p[1] + (p[2] & (__force u16)htons(0x00ff));
+       __u32 i = (length >> 1) - 3; /* Number of remaining complete words */
+
+       /* Loop through them */
+       p += 3;
+       while (i--)
                sum += *p++;
 
        /* Add on the last part word if it exists */
        if (packet->ipx_pktsize & htons(1))
-               sum += ntohs(0xff00) & *p;
+               sum += (__force u16)htons(0xff00) & *p;
 
        /* Do final fixup */
        sum = (sum & 0xffff) + (sum >> 16);
@@ -1263,7 +1263,14 @@ __u16 ipx_cksum(struct ipxhdr *packet, int length)
        if (sum >= 0x10000)
                sum++;
 
-       return ~sum;
+       /*
+        * Leave 0 alone; we don't want 0xffff here.  Note that we can't get
+        * here with 0x10000, so this check is the same as ((__u16)sum)
+        */
+       if (sum)
+               sum = ~sum;
+
+       return (__force __be16)sum;
 }
 
 const char *ipx_frame_name(__be16 frame)