[PATCH] vsock/virtio: add support for MSG_PEEK

This patch adds support for MSG_PEEK. In such a case, packets are not
removed from the rx_queue and credit updates are not sent.

Signed-off-by: Matias Ezequiel Vara Larsen <redacted>
---
 net/vmw_vsock/virtio_transport_common.c | 50 +++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 94cc0fa..938f2ed 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c

@@ -264,6 +264,50 @@ static int virtio_transport_send_credit_update(struct vsock_sock *vsk,
 }
 
 static ssize_t
+virtio_transport_stream_do_peek(struct vsock_sock *vsk,
+				struct msghdr *msg,
+				size_t len)
+{
+	struct virtio_vsock_sock *vvs = vsk->trans;
+	struct virtio_vsock_pkt *pkt;
+	size_t bytes, total = 0;
+	int err = -EFAULT;
+
+	spin_lock_bh(&vvs->rx_lock);
+
+	list_for_each_entry(pkt, &vvs->rx_queue, list) {
+		if (total == len)
+			break;
+
+		bytes = len - total;
+		if (bytes > pkt->len - pkt->off)
+			bytes = pkt->len - pkt->off;
+
+		/* 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);
+
+		err = memcpy_to_msg(msg, pkt->buf + pkt->off, bytes);
+		if (err)
+			goto out;
+
+		spin_lock_bh(&vvs->rx_lock);
+
+		total += bytes;
+	}
+
+	spin_unlock_bh(&vvs->rx_lock);
+
+	return total;
+
+out:
+	if (total)
+		err = total;
+	return err;
+}
+
+static ssize_t
 virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 				   struct msghdr *msg,
 				   size_t len)

@@ -330,9 +374,9 @@ virtio_transport_stream_dequeue(struct vsock_sock *vsk,
 				size_t len, int flags)
 {
 	if (flags & MSG_PEEK)
-		return -EOPNOTSUPP;
-
-	return virtio_transport_stream_do_dequeue(vsk, msg, len);
+		return virtio_transport_stream_do_peek(vsk, msg, len);
+	else
+		return virtio_transport_stream_do_dequeue(vsk, msg, len);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_stream_dequeue);
 

-- 
2.7.4

On 9/26/19 11:23 AM, Matias Ezequiel Vara Larsen wrote:

This seems buggy to me.

virtio_transport_recv_enqueue() seems to be able to add payload to the last packet in the queue.

The loop you wrote here would miss newly added chunks while the vvs->rx_lock spinlock has been released.

virtio_transport_stream_do_dequeue() is ok, because it makes sure pkt->off == pkt->len
before cleaning the packet from the queue.

On Thu, Sep 26, 2019 at 12:33:36PM -0700, Eric Dumazet wrote:

On 9/26/19 11:23 AM, Matias Ezequiel Vara Larsen wrote:

quoted

This patch adds support for MSG_PEEK. In such a case, packets are not
removed from the rx_queue and credit updates are not sent.

Signed-off-by: Matias Ezequiel Vara Larsen <redacted>
---
 net/vmw_vsock/virtio_transport_common.c | 50 +++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 94cc0fa..938f2ed 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c

@@ -264,6 +264,50 @@ static int virtio_transport_send_credit_update(struct vsock_sock *vsk,
 }
 
 static ssize_t
+virtio_transport_stream_do_peek(struct vsock_sock *vsk,
+				struct msghdr *msg,
+				size_t len)
+{
+	struct virtio_vsock_sock *vvs = vsk->trans;
+	struct virtio_vsock_pkt *pkt;
+	size_t bytes, total = 0;
+	int err = -EFAULT;
+
+	spin_lock_bh(&vvs->rx_lock);
+
+	list_for_each_entry(pkt, &vvs->rx_queue, list) {
+		if (total == len)
+			break;
+
+		bytes = len - total;
+		if (bytes > pkt->len - pkt->off)
+			bytes = pkt->len - pkt->off;
+
+		/* 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);
+
+		err = memcpy_to_msg(msg, pkt->buf + pkt->off, bytes);
+		if (err)
+			goto out;
+
+		spin_lock_bh(&vvs->rx_lock);
+
+		total += bytes;
+	}
+
+	spin_unlock_bh(&vvs->rx_lock);
+
+	return total;
+
+out:
+	if (total)
+		err = total;
+	return err;
+}

This seems buggy to me.

virtio_transport_recv_enqueue() seems to be able to add payload to the last packet in the queue.

The loop you wrote here would miss newly added chunks while the vvs->rx_lock spinlock has been released.

virtio_transport_stream_do_dequeue() is ok, because it makes sure pkt->off == pkt->len
before cleaning the packet from the queue.

Good catch!

Maybe we can solve in this way:

	list_for_each_entry(pkt, &vvs->rx_queue, list) {
		size_t off = pkt->off;

		if (total == len)
			break;

		while (total < len && off < pkt->len) {
			/* using 'off' instead of 'pkt->off' */
			...

			total += bytes;
			off += bytes;
		}
	}

What do you think?

Cheers,
Stefano

On 9/27/19 1:55 AM, Stefano Garzarella wrote:

Good catch!

Maybe we can solve in this way:

	list_for_each_entry(pkt, &vvs->rx_queue, list) {
		size_t off = pkt->off;

		if (total == len)
			break;

		while (total < len && off < pkt->len) {
			/* using 'off' instead of 'pkt->off' */
			...

			total += bytes;
			off += bytes;
		}
	}

What do you think?

Maybe, but I need to see a complete patch, evil is in the details :)

On Fri, Sep 27, 2019 at 06:37:00AM -0700, Eric Dumazet wrote:

On 9/27/19 1:55 AM, Stefano Garzarella wrote:

quoted

Good catch!

Maybe we can solve in this way:

	list_for_each_entry(pkt, &vvs->rx_queue, list) {
		size_t off = pkt->off;

		if (total == len)
			break;

		while (total < len && off < pkt->len) {
			/* using 'off' instead of 'pkt->off' */
			...

			total += bytes;
			off += bytes;
		}
	}

What do you think?

Maybe, but I need to see a complete patch, evil is in the details :)

Thanks both for your comments, I will take them into account and submit
a second version. 

Matias

This patch adds support for MSG_PEEK. In such a case, packets are not
removed from the rx_queue and credit updates are not sent.

Signed-off-by: Matias Ezequiel Vara Larsen <redacted>
---
 net/vmw_vsock/virtio_transport_common.c | 55 +++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 94cc0fa..cf15751 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c

@@ -264,6 +264,55 @@ static int virtio_transport_send_credit_update(struct vsock_sock *vsk,
 }
 
 static ssize_t
+virtio_transport_stream_do_peek(struct vsock_sock *vsk,
+				struct msghdr *msg,
+				size_t len)
+{
+	struct virtio_vsock_sock *vvs = vsk->trans;
+	struct virtio_vsock_pkt *pkt;
+	size_t bytes, total = 0, off;
+	int err = -EFAULT;
+
+	spin_lock_bh(&vvs->rx_lock);
+
+	list_for_each_entry(pkt, &vvs->rx_queue, list) {
+		off = pkt->off;
+
+		if (total == len)
+			break;
+
+		while (total < len && off < pkt->len) {
+			bytes = len - total;
+			if (bytes > pkt->len - off)
+				bytes = pkt->len - off;
+
+			/* 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);
+
+			err = memcpy_to_msg(msg, pkt->buf + off, bytes);
+			if (err)
+				goto out;
+
+			spin_lock_bh(&vvs->rx_lock);
+
+			total += bytes;
+			off += bytes;
+		}
+	}
+
+	spin_unlock_bh(&vvs->rx_lock);
+
+	return total;
+
+out:
+	if (total)
+		err = total;
+	return err;
+}
+
+static ssize_t
 virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 				   struct msghdr *msg,
 				   size_t len)

@@ -330,9 +379,9 @@ virtio_transport_stream_dequeue(struct vsock_sock *vsk,
 				size_t len, int flags)
 {
 	if (flags & MSG_PEEK)
-		return -EOPNOTSUPP;
-
-	return virtio_transport_stream_do_dequeue(vsk, msg, len);
+		return virtio_transport_stream_do_peek(vsk, msg, len);
+	else
+		return virtio_transport_stream_do_dequeue(vsk, msg, len);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_stream_dequeue);
 

-- 
2.7.4

This is net-next material.

Hi Matias,

On Fri, Sep 27, 2019 at 04:44:23PM +0000, Matias Ezequiel Vara Larsen wrote:

This patch adds support for MSG_PEEK. In such a case, packets are not
removed from the rx_queue and credit updates are not sent.

Signed-off-by: Matias Ezequiel Vara Larsen <redacted>
---
 net/vmw_vsock/virtio_transport_common.c | 55 +++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 3 deletions(-)

The patch LGTM. As David pointed out, this patch should go into net-next.
Since now net-next is open, you can resend with net-next tag [1] and
with:

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Tested-by: Stefano Garzarella <sgarzare@redhat.com>

Thanks,
Stefano

[1] https://www.kernel.org/doc/Documentation/networking/netdev-FAQ.txt

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