On 2025/01/20 20:24, Willem de Bruijn wrote:

Akihiko Odaki wrote:

quoted

hdr_len is repeatedly used so keep it in a local variable.

Signed-off-by: Akihiko Odaki <redacted>
---
  drivers/net/tap.c | 17 +++++++----------
  1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 061c2f27dfc83f5e6d0bea4da0e845cc429b1fd8..7ee2e9ee2a89fd539b087496b92d2f6198266f44 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c

@@ -645,6 +645,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
  	int err;
  	struct virtio_net_hdr vnet_hdr = { 0 };
  	int vnet_hdr_len = 0;
+	int hdr_len = 0;
  	int copylen = 0;
  	int depth;
  	bool zerocopy = false;

@@ -672,6 +673,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
  		err = -EINVAL;
  		if (tap16_to_cpu(q, vnet_hdr.hdr_len) > iov_iter_count(from))
  			goto err;
+		hdr_len = tap16_to_cpu(q, vnet_hdr.hdr_len);
  	}
  
  	len = iov_iter_count(from);

@@ -683,11 +685,8 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
  	if (msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
  		struct iov_iter i;
  
-		copylen = vnet_hdr.hdr_len ?
-			tap16_to_cpu(q, vnet_hdr.hdr_len) : GOODCOPY_LEN;
-		if (copylen > good_linear)
-			copylen = good_linear;
-		else if (copylen < ETH_HLEN)
+		copylen = min(hdr_len ? hdr_len : GOODCOPY_LEN, good_linear);
+		if (copylen < ETH_HLEN)
  			copylen = ETH_HLEN;
  		linear = copylen;
  		i = *from;

@@ -698,11 +697,9 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
  
  	if (!zerocopy) {
  		copylen = len;
-		linear = tap16_to_cpu(q, vnet_hdr.hdr_len);
-		if (linear > good_linear)
-			linear = good_linear;
-		else if (linear < ETH_HLEN)
-			linear = ETH_HLEN;
+		linear = min(hdr_len, good_linear);
+		if (copylen < ETH_HLEN)
+			copylen = ETH_HLEN;

Similar to previous patch, I don't think this patch is significant
enough to warrant the code churn.

The following patch will require replacing
tap16_to_cpu(q, vnet_hdr.hdr_len)
with
tap16_to_cpu(q->flags, vnet_hdr.hdr_len)

It will make some lines a bit too long. Calling tap16_to_cpu() at 
multiple places is also not good to keep the vnet implementation unified 
as the function inspects vnet_hdr.

This patch is independently too trivial, but I think it is a worthwhile 
cleanup combined with the following patch.