net: helper function skb_len_add

Move the len fields manipulation in the skbs to a helper function.
There is a comment specifically requesting this and there are several
other areas in the code displaying the same pattern which can be
refactored.
This improves code readability.
Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
Link: https://lore.kernel.org/r/20220622160853.GA6478@debianSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/skbuff.h

@@ -2351,6 +2351,18 @@ static inline unsigned int skb_pagelen(const struct sk_buff *skb)
 	return skb_headlen(skb) + __skb_pagelen(skb);
 }
 
+/**
+ * skb_len_add - adds a number to len fields of skb
+ * @skb: buffer to add len to
+ * @delta: number of bytes to add
+ */
+static inline void skb_len_add(struct sk_buff *skb, int delta)
+{
+	skb->len += delta;
+	skb->data_len += delta;
+	skb->truesize += delta;
+}
+
 /**
  * __skb_fill_page_desc - initialise a paged fragment in an skb
  * @skb: buffer containing fragment to be initialised

include/net/sock.h

@@ -2219,9 +2219,7 @@ static inline int skb_copy_to_page_nocache(struct sock *sk, struct iov_iter *fro
 	if (err)
 		return err;
 
-	skb->len	     += copy;
-	skb->data_len	     += copy;
-	skb->truesize	     += copy;
+	skb_len_add(skb, copy);
 	sk_wmem_queued_add(sk, copy);
 	sk_mem_charge(sk, copy);
 	return 0;

net/core/skbuff.c

@@ -3195,9 +3195,7 @@ skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen)
 		}
 	}
 
-	to->truesize += len + plen;
-	to->len += len + plen;
-	to->data_len += len + plen;
+	skb_len_add(to, len + plen);
 
 	if (unlikely(skb_orphan_frags(from, GFP_ATOMIC))) {
 		skb_tx_error(from);
@@ -3634,13 +3632,8 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
 	tgt->ip_summed = CHECKSUM_PARTIAL;
 	skb->ip_summed = CHECKSUM_PARTIAL;
 
-	/* Yak, is it really working this way? Some helper please? */
-	skb->len -= shiftlen;
-	skb->data_len -= shiftlen;
-	skb->truesize -= shiftlen;
-	tgt->len += shiftlen;
-	tgt->data_len += shiftlen;
-	tgt->truesize += shiftlen;
+	skb_len_add(skb, -shiftlen);
+	skb_len_add(tgt, shiftlen);
 
 	return shiftlen;
 }

net/ipv4/esp4.c

@@ -502,9 +502,7 @@ int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
 
 			nfrags++;
 
-			skb->len += tailen;
-			skb->data_len += tailen;
-			skb->truesize += tailen;
+			skb_len_add(skb, tailen);
 			if (sk && sk_fullsock(sk))
 				refcount_add(tailen, &sk->sk_wmem_alloc);
 

net/ipv4/ip_output.c

@@ -1214,9 +1214,7 @@ static int __ip_append_data(struct sock *sk,
 
 			pfrag->offset += copy;
 			skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
-			skb->len += copy;
-			skb->data_len += copy;
-			skb->truesize += copy;
+			skb_len_add(skb, copy);
 			wmem_alloc_delta += copy;
 		} else {
 			err = skb_zerocopy_iter_dgram(skb, from, copy);
@@ -1443,9 +1441,7 @@ ssize_t	ip_append_page(struct sock *sk, struct flowi4 *fl4, struct page *page,
 			skb->csum = csum_block_add(skb->csum, csum, skb->len);
 		}
 
-		skb->len += len;
-		skb->data_len += len;
-		skb->truesize += len;
+		skb_len_add(skb, len);
 		refcount_add(len, &sk->sk_wmem_alloc);
 		offset += len;
 		size -= len;