linux-kernel - Re: [RFC PATCH v1 1/4] virtio/vsock: rework MSG_PEEK for SOCK

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Date:   Mon, 26 Jun 2023 18:23:32 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>,
        Bobby Eshleman <bobby.eshleman@...edance.com>
Cc:     Stefan Hajnoczi <stefanha@...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>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...rdevices.ru, oxffffaa@...il.com
Subject: Re: [RFC PATCH v1 1/4] virtio/vsock: rework MSG_PEEK for SOCK_STREAM

On Sun, Jun 18, 2023 at 09:24:48AM +0300, Arseniy Krasnov wrote:
>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>
>---
> net/vmw_vsock/virtio_transport_common.c | 41 ++++++++++++-------------
> 1 file changed, 19 insertions(+), 22 deletions(-)

Great clean up!

LGTM, but @Bobby can you also take a look?

Thanks,
Stefano

>
>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
>