macvtap: zerocopy: fix offset calculation when building skb

This patch fixes the offset calculation when building skb:

- offset1 were used as skb data offset not vector offset
- reset offset to zero only when we advance to next vector

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 7 insertions, 6 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 0427c6561c84..bd4a70d8605f 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -505,10 +505,11 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
                 if (copy > size) {
                         ++from;
                         --count;
-                }
+                        offset = 0;
+                } else
+                        offset += size;
                 copy -= size;
                 offset1 += size;
-                offset = 0;
         }
 
         if (len == offset1)
@@ -519,13 +520,13 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
                 int num_pages;
                 unsigned long base;
 
-                len = from->iov_len - offset1;
+                len = from->iov_len - offset;
                 if (!len) {
-                        offset1 = 0;
+                        offset = 0;
                         ++from;
                         continue;
                 }
-                base = (unsigned long)from->iov_base + offset1;
+                base = (unsigned long)from->iov_base + offset;
                 size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
                 num_pages = get_user_pages_fast(base, size, 0, &page[i]);
                 if ((num_pages != size) ||
@@ -546,7 +547,7 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
                         len -= size;
                         i++;
                 }
-                offset1 = 0;
+                offset = 0;
                 ++from;
         }
         return 0;