linux-kernel - [RFC PATCH v2 1/4] virtio/vsock: rework MSG_PEEK for SOCK

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Message-ID: <20230719192708.1775162-2-AVKrasnov@sberdevices.ru>
Date:   Wed, 19 Jul 2023 22:27:05 +0300
From:   Arseniy Krasnov <AVKrasnov@...rdevices.ru>
To:     Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...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>,
        Jason Wang <jasowang@...hat.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>
CC:     <kvm@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel@...rdevices.ru>, <oxffffaa@...il.com>,
        <avkrasnov@...rdevices.ru>,
        Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Subject: [RFC PATCH v2 1/4] virtio/vsock: rework MSG_PEEK for SOCK_STREAM

This reworks current implementation of MSG_PEEK logic:
1) Replaces 'skb_queue_walk_safe()' with 'skb_queue_walk()'. There is
   no need in the first one, as there are no removes of skb in loop.
2) Removes nested while loop - MSG_PEEK logic could be implemented
   without it: just iterate over skbs without removing it and copy
   data from each until destination buffer is not full.

Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Reviewed-by: Bobby Eshleman <bobby.eshleman@...edance.com>
---
 net/vmw_vsock/virtio_transport_common.c | 41 ++++++++++++-------------
 1 file changed, 19 insertions(+), 22 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index b769fc258931..2ee40574c339 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -348,37 +348,34 @@ virtio_transport_stream_do_peek(struct vsock_sock *vsk,
 				size_t len)
 {
 	struct virtio_vsock_sock *vvs = vsk->trans;
-	size_t bytes, total = 0, off;
-	struct sk_buff *skb, *tmp;
-	int err = -EFAULT;
+	struct sk_buff *skb;
+	size_t total = 0;
+	int err;
 
 	spin_lock_bh(&vvs->rx_lock);
 
-	skb_queue_walk_safe(&vvs->rx_queue, skb,  tmp) {
-		off = 0;
+	skb_queue_walk(&vvs->rx_queue, skb) {
+		size_t bytes;
 
-		if (total == len)
-			break;
+		bytes = len - total;
+		if (bytes > skb->len)
+			bytes = skb->len;
 
-		while (total < len && off < skb->len) {
-			bytes = len - total;
-			if (bytes > skb->len - off)
-				bytes = skb->len - off;
+		spin_unlock_bh(&vvs->rx_lock);
 
-			/* sk_lock is held by caller so no one else can dequeue.
-			 * Unlock rx_lock since memcpy_to_msg() may sleep.
-			 */
-			spin_unlock_bh(&vvs->rx_lock);
+		/* sk_lock is held by caller so no one else can dequeue.
+		 * Unlock rx_lock since memcpy_to_msg() may sleep.
+		 */
+		err = memcpy_to_msg(msg, skb->data, bytes);
+		if (err)
+			goto out;
 
-			err = memcpy_to_msg(msg, skb->data + off, bytes);
-			if (err)
-				goto out;
+		total += bytes;
 
-			spin_lock_bh(&vvs->rx_lock);
+		spin_lock_bh(&vvs->rx_lock);
 
-			total += bytes;
-			off += bytes;
-		}
+		if (total == len)
+			break;
 	}
 
 	spin_unlock_bh(&vvs->rx_lock);
-- 
2.25.1