[PATCH v6 3/5] checksum: Add an offset argument in csum_iov()

[Laurent Vivier <lvivier@redhat.com>]

The offset allows any headers that are not part of the data
to checksum to be skipped.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---

Notes:
    v5:
      - correctly set the length for the partial csum_unfolded()
    v3:
      - reorder @offset and @init
    v2:
      - check iov_skip_bytes() return value

 checksum.c | 16 ++++++++++++++--
 checksum.h |  3 ++-
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/checksum.c b/checksum.c
index 006614fcbb28..05d002ab0c25 100644
--- a/checksum.c
+++ b/checksum.c
@@ -59,6 +59,7 @@
 #include "util.h"
 #include "ip.h"
 #include "checksum.h"
+#include "iov.h"
 
 /* Checksums are optional for UDP over IPv4, so we usually just set
  * them to 0.  Change this to 1 to calculate real UDP over IPv4
@@ -497,16 +498,27 @@ uint16_t csum(const void *buf, size_t len, uint32_t init)
  *
  * @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
  * @init	Initial 32-bit checksum, 0 for no pre-computed checksum
  *
  * Return: 16-bit folded, complemented checksum
  */
 /* cppcheck-suppress unusedFunction */
-uint16_t csum_iov(const struct iovec *iov, size_t n, uint32_t init)
+uint16_t csum_iov(const struct iovec *iov, size_t n, size_t offset,
+		  uint32_t init)
 {
 	unsigned int i;
+	size_t first;
 
-	for (i = 0; i < n; i++)
+	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);
 
 	return (uint16_t)~csum_fold(init);
diff --git a/checksum.h b/checksum.h
index c5964ac78921..49f7472dd1b6 100644
--- a/checksum.h
+++ b/checksum.h
@@ -32,6 +32,7 @@ void csum_icmp6(struct icmp6hdr *icmp6hr,
 		const void *payload, size_t dlen);
 uint32_t csum_unfolded(const void *buf, size_t len, uint32_t init);
 uint16_t csum(const void *buf, size_t len, uint32_t init);
-uint16_t csum_iov(const struct iovec *iov, size_t n, uint32_t init);
+uint16_t csum_iov(const struct iovec *iov, size_t n, size_t offset,
+		  uint32_t init);
 
 #endif /* CHECKSUM_H */
-- 
@@ -32,6 +32,7 @@ void csum_icmp6(struct icmp6hdr *icmp6hr,
 		const void *payload, size_t dlen);
 uint32_t csum_unfolded(const void *buf, size_t len, uint32_t init);
 uint16_t csum(const void *buf, size_t len, uint32_t init);
-uint16_t csum_iov(const struct iovec *iov, size_t n, uint32_t init);
+uint16_t csum_iov(const struct iovec *iov, size_t n, size_t offset,
+		  uint32_t init);
 
 #endif /* CHECKSUM_H */
-- 
2.46.0