iov, checksum: Replace csum_iov() with csum_iov_tail()

We usually want to checksum only the tail part of a frame, excluding at
least some headers.  csum_iov() does that for a frame represented as an
IO vector, not actually summing the entire IO vector.  We now have struct
iov_tail to explicitly represent this construct, so replace csum_iov()
with csum_iov_tail() taking that representation rather than 3 parameters.

We propagate the same change to csum_udp4() and csum_udp6() which take
similar parameters.  This slightly simplifies the code, and will allow some
further simplifications as struct iov_tail is more widely used.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 23 insertions, 35 deletions

diff --git a/checksum.c b/checksum.c
index c673993..1c4354d 100644
--- a/checksum.c
+++ b/checksum.c
@@ -166,24 +166,22 @@ uint32_t proto_ipv4_header_psum(uint16_t l4len, uint8_t protocol,
  * @udp4hr:	UDP header, initialised apart from checksum
  * @saddr:	IPv4 source address
  * @daddr:	IPv4 destination address
- * @iov:	Pointer to the array of IO vectors
- * @iov_cnt:	Length of the array
- * @offset:	UDP payload offset in the iovec array
+ * @data:	UDP payload (as IO vector tail)
  */
 void csum_udp4(struct udphdr *udp4hr,
 	       struct in_addr saddr, struct in_addr daddr,
-	       const struct iovec *iov, int iov_cnt, size_t offset)
+	       struct iov_tail *data)
 {
 	/* UDP checksums are optional, so don't bother */
 	udp4hr->check = 0;
 
 	if (UDP4_REAL_CHECKSUMS) {
-		uint16_t l4len = iov_size(iov, iov_cnt) - offset +
-				 sizeof(struct udphdr);
+		uint16_t l4len = iov_tail_size(data) + sizeof(struct udphdr);
 		uint32_t psum = proto_ipv4_header_psum(l4len, IPPROTO_UDP,
 						       saddr, daddr);
+
 		psum = csum_unfolded(udp4hr, sizeof(struct udphdr), psum);
-		udp4hr->check = csum_iov(iov, iov_cnt, offset, psum);
+		udp4hr->check = csum_iov_tail(data, psum);
 	}
 }
 
@@ -231,22 +229,20 @@ uint32_t proto_ipv6_header_psum(uint16_t payload_len, uint8_t protocol,
  * @udp6hr:	UDP header, initialised apart from checksum
  * @saddr:	Source address
  * @daddr:	Destination address
- * @iov:	Pointer to the array of IO vectors
- * @iov_cnt:	Length of the array
- * @offset:	UDP payload offset in the iovec array
+ * @data:	UDP payload (as IO vector tail)
  */
 void csum_udp6(struct udphdr *udp6hr,
 	       const struct in6_addr *saddr, const struct in6_addr *daddr,
-	       const struct iovec *iov, int iov_cnt, size_t offset)
+	       struct iov_tail *data)
 {
-	uint16_t l4len = iov_size(iov, iov_cnt) - offset +
-			 sizeof(struct udphdr);
+	uint16_t l4len = iov_tail_size(data) + sizeof(struct udphdr);
 	uint32_t psum = proto_ipv6_header_psum(l4len, IPPROTO_UDP,
 					       saddr, daddr);
+
 	udp6hr->check = 0;
 
 	psum = csum_unfolded(udp6hr, sizeof(struct udphdr), psum);
-	udp6hr->check = csum_iov(iov, iov_cnt, offset, psum);
+	udp6hr->check = csum_iov_tail(data, psum);
 }
 
 /**
@@ -501,31 +497,23 @@ uint16_t csum(const void *buf, size_t len, uint32_t init)
 }
 
 /**
- * csum_iov() - Calculates the unfolded checksum over an array of IO vectors
- *
- * @iov		Pointer to the array of IO vectors
- * @n		Length of the array
- * @offset:	Offset of the data to checksum within the full data length
+ * csum_iov_tail() - Calculate unfolded checksum for the tail of an IO vector
+ * @tail:	IO vector tail to checksum
  * @init	Initial 32-bit checksum, 0 for no pre-computed checksum
  *
  * Return: 16-bit folded, complemented checksum
  */
-uint16_t csum_iov(const struct iovec *iov, size_t n, size_t offset,
-		  uint32_t init)
+uint16_t csum_iov_tail(struct iov_tail *tail, uint32_t init)
 {
-	unsigned int i;
-	size_t first;
-
-	i = iov_skip_bytes(iov, n, offset, &first);
-	if (i >= n)
-		return (uint16_t)~csum_fold(init);
-
-	init = csum_unfolded((char *)iov[i].iov_base + first,
-			     iov[i].iov_len - first, init);
-	i++;
-
-	for (; i < n; i++)
-		init = csum_unfolded(iov[i].iov_base, iov[i].iov_len, init);
-
+	if (iov_tail_prune(tail)) {
+		size_t i;
+
+		init = csum_unfolded((char *)tail->iov[0].iov_base + tail->off,
+				     tail->iov[0].iov_len - tail->off, init);
+		for (i = 1; i < tail->cnt; i++) {
+			const struct iovec *iov = &tail->iov[i];
+			init = csum_unfolded(iov->iov_base, iov->iov_len, init);
+		}
+	}
 	return (uint16_t)~csum_fold(init);
 }