linux-kernel - [PATCH net v3 8/9] tap: Keep hdr_len in tap_get

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Message-Id: <20250116-tun-v3-8-c6b2871e97f7@daynix.com>
Date: Thu, 16 Jan 2025 17:08:11 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Jonathan Corbet <corbet@....net>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Jason Wang <jasowang@...hat.com>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, 
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>, 
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 netdev@...r.kernel.org, kvm@...r.kernel.org, 
 virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, 
 Yuri Benditovich <yuri.benditovich@...nix.com>, 
 Andrew Melnychenko <andrew@...nix.com>, 
 Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com, 
 devel@...nix.com, Akihiko Odaki <akihiko.odaki@...nix.com>
Subject: [PATCH net v3 8/9] tap: Keep hdr_len in tap_get_user()

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

Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
---
 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 061c2f27dfc8..7ee2e9ee2a89 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;
 	}

 	skb = tap_alloc_skb(&q->sk, TAP_RESERVE, copylen,

-- 
2.47.1