[PATCH RFC net-next] net: use helper skb_ensure_writable in skb_checksum_help and skb_crc32c_csum_help

[PATCH RFC net-next] net: use helper skb_ensure_writable in skb_checksum_help and skb_crc32c_csum_help

[Heiner Kallweit]

Instead of open-coding making the checksum writable we can use an
appropriate helper. skb_ensure_writable is a candidate, however we
might also use skb_header_unclone. Hints welcome.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 net/core/dev.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index fc676b261..90516a800 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2939,12 +2939,9 @@ int skb_checksum_help(struct sk_buff *skb)
 	offset += skb->csum_offset;
 	BUG_ON(offset + sizeof(__sum16) > skb_headlen(skb));
 
-	if (skb_cloned(skb) &&
-	    !skb_clone_writable(skb, offset + sizeof(__sum16))) {
-		ret = pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
-		if (ret)
-			goto out;
-	}
+	ret = skb_ensure_writable(skb, offset + sizeof(__sum16));
+	if (ret)
+		goto out;
 
 	*(__sum16 *)(skb->data + offset) = csum_fold(csum) ?: CSUM_MANGLED_0;
 out_set_summed:
@@ -2979,12 +2976,11 @@ int skb_crc32c_csum_help(struct sk_buff *skb)
 		ret = -EINVAL;
 		goto out;
 	}
-	if (skb_cloned(skb) &&
-	    !skb_clone_writable(skb, offset + sizeof(__le32))) {
-		ret = pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
-		if (ret)
-			goto out;
-	}
+
+	ret = skb_ensure_writable(skb, offset + sizeof(__le32));
+	if (ret)
+		goto out;
+
 	crc32c_csum = cpu_to_le32(~__skb_checksum(skb, start,
 						  skb->len - start, ~(__u32)0,
 						  crc32c_csum_stub));
-- 
2.22.0

Re: [PATCH RFC net-next] net: use helper skb_ensure_writable in skb_checksum_help and skb_crc32c_csum_help

[David Miller]

From: Heiner Kallweit <hkallweit1@gmail.com>
Date: Wed, 24 Jul 2019 23:47:49 +0200

> Instead of open-coding making the checksum writable we can use an
> appropriate helper. skb_ensure_writable is a candidate, however we
> might also use skb_header_unclone. Hints welcome.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

FWIW these conversions look accurate to me.

The only real difference is the perhaps unnecessary pskb_may_pull()
check.