Re: [PATCH RFC net-next v5 07/14] virtio/vsock: add common datagram send path

Arseniy Krasnov
2023-07-22T08:16:12Z

On 19.07.2023 03:50, Bobby Eshleman wrote:
> This commit implements the common function
> virtio_transport_dgram_enqueue for enqueueing datagrams. It does not add
> usage in either vhost or virtio yet.
>
> Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> ---
> net/vmw_vsock/virtio_transport_common.c | 76 ++++++++++++++++++++++++++++++++-
> 1 file changed, 75 insertions(+), 1 deletion(-)
>
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index ffcbdd77feaa..3bfaff758433 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -819,7 +819,81 @@ virtio_transport_dgram_enqueue(struct vsock_sock *vsk,
> struct msghdr *msg,
> size_t dgram_len)
> {
> - return -EOPNOTSUPP;
> + /* Here we are only using the info struct to retain style uniformity
> + * and to ease future refactoring and merging.
> + */
> + struct virtio_vsock_pkt_info info_stack = {
> + .op = VIRTIO_VSOCK_OP_RW,
> + .msg = msg,
> + .vsk = vsk,
> + .type = VIRTIO_VSOCK_TYPE_DGRAM,
> + };
> + const struct virtio_transport *t_ops;
> + struct virtio_vsock_pkt_info *info;
> + struct sock *sk = sk_vsock(vsk);
> + struct virtio_vsock_hdr *hdr;
> + u32 src_cid, src_port;
> + struct sk_buff *skb;
> + void *payload;
> + int noblock;
> + int err;
> +
> + info = &info_stack;

I think 'info' assignment could be moved below, to the place where it is used
first time.

> +
> + if (dgram_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
> + return -EMSGSIZE;
> +
> + t_ops = virtio_transport_get_ops(vsk);
> + if (unlikely(!t_ops))
> + return -EFAULT;
> +
> + /* Unlike some of our other sending functions, this function is not
> + * intended for use without a msghdr.
> + */
> + if (WARN_ONCE(!msg, "vsock dgram bug: no msghdr found for dgram enqueue\n"))
> + return -EFAULT;

Sorry, but is that possible? I thought 'msg' is always provided by general socket layer (e.g. before
af_vsock.c code) and can't be NULL for DGRAM. Please correct me if i'm wrong.

Also I see, that in af_vsock.c , 'vsock_dgram_sendmsg()' dereferences 'msg' for checking MSG_OOB without any
checks (before calling transport callback - this function in case of virtio). So I think if we want to keep
this type of check - such check must be placed in af_vsock.c or somewhere before first dereference of this pointer.

> +
> + noblock = msg->msg_flags & MSG_DONTWAIT;
> +
> + /* Use sock_alloc_send_skb to throttle by sk_sndbuf. This helps avoid
> + * triggering the OOM.
> + */
> + skb = sock_alloc_send_skb(sk, dgram_len + VIRTIO_VSOCK_SKB_HEADROOM,
> + noblock, &err);
> + if (!skb)
> + return err;
> +
> + skb_reserve(skb, VIRTIO_VSOCK_SKB_HEADROOM);
> +
> + src_cid = t_ops->transport.get_local_cid();
> + src_port = vsk->local_addr.svm_port;
> +
> + hdr = virtio_vsock_hdr(skb);
> + hdr->type = cpu_to_le16(info->type);
> + hdr->op = cpu_to_le16(info->op);
> + hdr->src_cid = cpu_to_le64(src_cid);
> + hdr->dst_cid = cpu_to_le64(remote_addr->svm_cid);
> + hdr->src_port = cpu_to_le32(src_port);
> + hdr->dst_port = cpu_to_le32(remote_addr->svm_port);
> + hdr->flags = cpu_to_le32(info->flags);
> + hdr->len = cpu_to_le32(dgram_len);
> +
> + skb_set_owner_w(skb, sk);
> +
> + payload = skb_put(skb, dgram_len);
> + err = memcpy_from_msg(payload, msg, dgram_len);
> + if (err)
> + return err;

Do we need free allocated skb here ?

> +
> + trace_virtio_transport_alloc_pkt(src_cid, src_port,
> + remote_addr->svm_cid,
> + remote_addr->svm_port,
> + dgram_len,
> + info->type,
> + info->op,
> + 0);
> +
> + return t_ops->send_pkt(skb);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_dgram_enqueue);
>
>

Thanks, Arseniy