net: Use skb_checksum_start_offset()

Replace skb->csum_start - skb_headroom(skb) with skb_checksum_start_offset().

Note for usb/smsc95xx: skb->data - skb->head == skb_headroom(skb).

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 4 deletions

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index 65cb1abfbe57..bc86f4b6ecc2 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1163,9 +1163,8 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 
 static u32 smsc95xx_calc_csum_preamble(struct sk_buff *skb)
 {
-        int len = skb->data - skb->head;
-        u16 high_16 = (u16)(skb->csum_offset + skb->csum_start - len);
-        u16 low_16 = (u16)(skb->csum_start - len);
+        u16 low_16 = (u16)skb_checksum_start_offset(skb);
+        u16 high_16 = low_16 + skb->csum_offset;
         return (high_16 << 16) | low_16;
 }
 
@@ -1193,7 +1192,7 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
                 if (skb->len <= 45) {
                         /* workaround - hardware tx checksum does not work
                          * properly with extremely small packets */
-                        long csstart = skb->csum_start - skb_headroom(skb);
+                        long csstart = skb_checksum_start_offset(skb);
                         __wsum calc = csum_partial(skb->data + csstart,
                                 skb->len - csstart, 0);
                         *((__sum16 *)(skb->data + csstart