Re: [RFC PATCH net-next v6 09/14] virtio/vsock: add common datagram recv path

From: Stefano Garzarella
Date: Tue Jul 30 2024 - 04:36:19 EST

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In reply to: Amery Hung: "Re: [RFC PATCH net-next v6 09/14] virtio/vsock: add common datagram recv path"
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On Mon, Jul 29, 2024 at 05:35:01PM GMT, Amery Hung wrote:

On Tue, Jul 23, 2024 at 7:42 AM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote:

On Wed, Jul 10, 2024 at 09:25:50PM GMT, Amery Hung wrote:
>From: Bobby Eshleman <bobby.eshleman@xxxxxxxxxxxxx>
>
>This commit adds the common datagram receive functionality for virtio
>transports. It does not add the vhost/virtio users of that
>functionality.
>
>This functionality includes:
>- changes to the virtio_transport_recv_pkt() path for finding the
> bound socket receiver for incoming packets
>- virtio_transport_recv_pkt() saves the source cid and port to the
> control buffer for recvmsg() to initialize sockaddr_vm structure
> when using datagram
>
>Signed-off-by: Bobby Eshleman <bobby.eshleman@xxxxxxxxxxxxx>
>Signed-off-by: Amery Hung <amery.hung@xxxxxxxxxxxxx>
>---
> net/vmw_vsock/virtio_transport_common.c | 79 +++++++++++++++++++++----
> 1 file changed, 66 insertions(+), 13 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 46cd1807f8e3..a571b575fde9 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -235,7 +235,9 @@ EXPORT_SYMBOL_GPL(virtio_transport_deliver_tap_pkt);
>
> static u16 virtio_transport_get_type(struct sock *sk)
> {
>- if (sk->sk_type == SOCK_STREAM)
>+ if (sk->sk_type == SOCK_DGRAM)
>+ return VIRTIO_VSOCK_TYPE_DGRAM;
>+ else if (sk->sk_type == SOCK_STREAM)
> return VIRTIO_VSOCK_TYPE_STREAM;
> else
> return VIRTIO_VSOCK_TYPE_SEQPACKET;
>@@ -1422,6 +1424,33 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
> kfree_skb(skb);
> }
>
>+static void
>+virtio_transport_dgram_kfree_skb(struct sk_buff *skb, int err)
>+{
>+ if (err == -ENOMEM)
>+ kfree_skb_reason(skb, SKB_DROP_REASON_SOCKET_RCVBUFF);
>+ else if (err == -ENOBUFS)
>+ kfree_skb_reason(skb, SKB_DROP_REASON_PROTO_MEM);
>+ else
>+ kfree_skb(skb);
>+}
>+
>+/* This function takes ownership of the skb.
>+ *
>+ * It either places the skb on the sk_receive_queue or frees it.
>+ */
>+static void
>+virtio_transport_recv_dgram(struct sock *sk, struct sk_buff *skb)
>+{
>+ int err;
>+
>+ err = sock_queue_rcv_skb(sk, skb);
>+ if (err) {
>+ virtio_transport_dgram_kfree_skb(skb, err);
>+ return;
>+ }
>+}
>+
> static int
> virtio_transport_recv_connected(struct sock *sk,
> struct sk_buff *skb)
>@@ -1591,7 +1620,8 @@ virtio_transport_recv_listen(struct sock *sk, struct sk_buff *skb,
> static bool virtio_transport_valid_type(u16 type)
> {
> return (type == VIRTIO_VSOCK_TYPE_STREAM) ||
>- (type == VIRTIO_VSOCK_TYPE_SEQPACKET);
>+ (type == VIRTIO_VSOCK_TYPE_SEQPACKET) ||
>+ (type == VIRTIO_VSOCK_TYPE_DGRAM);
> }
>
> /* We are under the virtio-vsock's vsock->rx_lock or vhost-vsock's vq->mutex
>@@ -1601,44 +1631,57 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
> struct sk_buff *skb)
> {
> struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
>+ struct vsock_skb_cb *vsock_cb;

This can be defined in the block where it's used.

Got it.

> struct sockaddr_vm src, dst;
> struct vsock_sock *vsk;
> struct sock *sk;
> bool space_available;
>+ u16 type;
>
> vsock_addr_init(&src, le64_to_cpu(hdr->src_cid),
> le32_to_cpu(hdr->src_port));
> vsock_addr_init(&dst, le64_to_cpu(hdr->dst_cid),
> le32_to_cpu(hdr->dst_port));
>
>+ type = le16_to_cpu(hdr->type);
>+
> trace_virtio_transport_recv_pkt(src.svm_cid, src.svm_port,
> dst.svm_cid, dst.svm_port,
> le32_to_cpu(hdr->len),
>- le16_to_cpu(hdr->type),
>+ type,
> le16_to_cpu(hdr->op),
> le32_to_cpu(hdr->flags),
> le32_to_cpu(hdr->buf_alloc),
> le32_to_cpu(hdr->fwd_cnt));
>
>- if (!virtio_transport_valid_type(le16_to_cpu(hdr->type))) {
>+ if (!virtio_transport_valid_type(type)) {
> (void)virtio_transport_reset_no_sock(t, skb);
> goto free_pkt;
> }
>
>- /* The socket must be in connected or bound table
>- * otherwise send reset back
>+ /* For stream/seqpacket, the socket must be in connected or bound table
>+ * otherwise send reset back.
>+ *
>+ * For datagrams, no reset is sent back.
> */
> sk = vsock_find_connected_socket(&src, &dst);
> if (!sk) {
>- sk = vsock_find_bound_socket(&dst);
>- if (!sk) {
>- (void)virtio_transport_reset_no_sock(t, skb);
>- goto free_pkt;
>+ if (type == VIRTIO_VSOCK_TYPE_DGRAM) {
>+ sk = vsock_find_bound_dgram_socket(&dst);
>+ if (!sk)
>+ goto free_pkt;
>+ } else {
>+ sk = vsock_find_bound_socket(&dst);
>+ if (!sk) {
>+ (void)virtio_transport_reset_no_sock(t, skb);
>+ goto free_pkt;
>+ }
> }
> }
>
>- if (virtio_transport_get_type(sk) != le16_to_cpu(hdr->type)) {
>- (void)virtio_transport_reset_no_sock(t, skb);
>+ if (virtio_transport_get_type(sk) != type) {
>+ if (type != VIRTIO_VSOCK_TYPE_DGRAM)
>+ (void)virtio_transport_reset_no_sock(t, skb);
> sock_put(sk);
> goto free_pkt;
> }
>@@ -1654,12 +1697,21 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
>
> /* Check if sk has been closed before lock_sock */
> if (sock_flag(sk, SOCK_DONE)) {
>- (void)virtio_transport_reset_no_sock(t, skb);
>+ if (type != VIRTIO_VSOCK_TYPE_DGRAM)
>+ (void)virtio_transport_reset_no_sock(t, skb);
> release_sock(sk);
> sock_put(sk);
> goto free_pkt;
> }
>
>+ if (sk->sk_type == SOCK_DGRAM) {
>+ vsock_cb = vsock_skb_cb(skb);
>+ vsock_cb->src_cid = src.svm_cid;
>+ vsock_cb->src_port = src.svm_port;
>+ virtio_transport_recv_dgram(sk, skb);

What about adding an API that transports can use to hide this?

I mean something that hide vsock_cb creation and queue packet in the
socket receive queue. I'd also not expose vsock_skb_cb in an header, but
I'd handle it internally in af_vsock.c. So I'd just expose API to
queue/dequeue them.

Got it. I will move vsock_skb_cb to af_vsock.c and create an API:

vsock_dgram_skb_save_src_addr(struct sk_buff *skb, u32 cid, u32 port)

This is okay, but I would try to go further by directly adding an API to queue dgrams in af_vsock.c (if it's feasible).

Different dgram implementations will call this API instead of the code
block above to save the source address information into the control
buffer.

A side note on why this is a vsock API instead of a member )unction in
transport: As we move to support multi-transport dgram, different
transport implementations can place skb into the sk->sk_receive_queue.
Therefore, we cannot call transport-specific function in
vsock_dgram_recvmsg() to initialize struct sockaddr_vm. Hence, the
receiving paths of different transports need to call this API to save
source address.

What I meant is, why virtio_transport_recv_dgram() can't be exposed by af_vsock.c as vsock_recv_dgram() and handle all internally, like populate vsock_cb, call sock_queue_rcv_skb(), etc.

Also why VMCI is using sk_receive_skb(), while we are using
sock_queue_rcv_skb()?

I _think_ originally we referred to UDP and UDS when designing virtio
dgram, and ended up with placing skb into sk_receive_queue directly. I
will look into this to provide better justification.

Great, thanks.

Maybe we can also ping VMCI maintainers to understand if they can switch to sock_queue_rcv_skb(). But we should understand better the difference.

Thanks,
Stefano

Next message: Sakari Ailus: "Re: [PATCH v2 0/2] MAX96714/7 style fixup"
Previous message: Liu Ying: "Re: [PATCH v2 09/16] drm/imx: Add i.MX8qxp Display Controller KMS"
In reply to: Amery Hung: "Re: [RFC PATCH net-next v6 09/14] virtio/vsock: add common datagram recv path"
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