netdev - Re: [PATCH net-next 2/2] net: mctp: Add MCTP USB transport driver

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Message-ID: <b78d0e25-f8cc-43af-90d8-2c7344895d55@suse.com>
Date: Thu, 6 Feb 2025 12:12:31 +0100
From: Oliver Neukum <oneukum@...e.com>
To: Jeremy Kerr <jk@...econstruct.com.au>,
 Matt Johnston <matt@...econstruct.com.au>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-usb@...r.kernel.org,
 Santosh Puranik <spuranik@...dia.com>
Subject: Re: [PATCH net-next 2/2] net: mctp: Add MCTP USB transport driver

On 06.02.25 07:48, Jeremy Kerr wrote:

Hi,

remarks inline.

	Regards
		Oliver

> +static void mctp_usb_in_complete(struct urb *urb)
> +{
> +	struct sk_buff *skb = urb->context;
> +	struct net_device *netdev = skb->dev;
> +	struct pcpu_dstats *dstats = this_cpu_ptr(netdev->dstats);
> +	struct mctp_usb *mctp_usb = netdev_priv(netdev);
> +	struct mctp_skb_cb *cb;
> +	unsigned int len;
> +	int status;
> +
> +	status = urb->status;
> +
> +	switch (status) {
> +	case -ENOENT:
> +	case -ECONNRESET:
> +	case -ESHUTDOWN:
> +	case -EPROTO:
> +		kfree_skb(skb);
> +		return;
> +	case 0:
> +		break;
> +	default:
> +		dev_err(&mctp_usb->usbdev->dev, "%s: urb status: %d\n",
> +			__func__, status);
> +		kfree_skb(skb);
> +		return;
> +	}
> +
> +	len = urb->actual_length;
> +	__skb_put(skb, len);
> +
> +	while (skb) {
> +		struct sk_buff *skb2 = NULL;
> +		struct mctp_usb_hdr *hdr;
> +		u8 pkt_len; /* length of MCTP packet, no USB header */
> +
> +		hdr = skb_pull_data(skb, sizeof(*hdr));
> +		if (!hdr)
> +			break;
> +
> +		if (be16_to_cpu(hdr->id) != MCTP_USB_DMTF_ID) {

It would be more efficient to do the conversion on the constant

> +			dev_dbg(&mctp_usb->usbdev->dev, "%s: invalid id %04x\n",
> +				__func__, be16_to_cpu(hdr->id));
> +			break;
> +		}
> +
> +		if (hdr->len <
> +		    sizeof(struct mctp_hdr) + sizeof(struct mctp_usb_hdr)) {
> +			dev_dbg(&mctp_usb->usbdev->dev,
> +				"%s: short packet (hdr) %d\n",
> +				__func__, hdr->len);
> +			break;
> +		}
> +
> +		/* we know we have at least sizeof(struct mctp_usb_hdr) here */
> +		pkt_len = hdr->len - sizeof(struct mctp_usb_hdr);
> +		if (pkt_len > skb->len) {
> +			dev_dbg(&mctp_usb->usbdev->dev,
> +				"%s: short packet (xfer) %d, actual %d\n",
> +				__func__, hdr->len, skb->len);
> +			break;
> +		}
> +
> +		if (pkt_len < skb->len) {
> +			/* more packets may follow - clone to a new
> +			 * skb to use on the next iteration
> +			 */
> +			skb2 = skb_clone(skb, GFP_ATOMIC);
> +			if (skb2) {
> +				if (!skb_pull(skb2, pkt_len)) {
> +					kfree_skb(skb2);
> +					skb2 = NULL;
> +				}
> +			}
> +			skb_trim(skb, pkt_len);

This is functional. Though in terms of algorithm you are copying
the same data multiple times.

> +		}
> +
> +		skb->protocol = htons(ETH_P_MCTP);
> +		skb_reset_network_header(skb);
> +		cb = __mctp_cb(skb);
> +		cb->halen = 0;
> +		netif_rx(skb);
> +
> +		u64_stats_update_begin(&dstats->syncp);
> +		u64_stats_inc(&dstats->rx_packets);
> +		u64_stats_add(&dstats->rx_bytes, skb->len);
> +		u64_stats_update_end(&dstats->syncp);
> +
> +		skb = skb2;
> +	}
> +
> +	if (skb)
> +		kfree_skb(skb);
> +
> +	mctp_usb_rx_queue(mctp_usb);
> +}
> +
> +static int mctp_usb_open(struct net_device *dev)
> +{
> +	struct mctp_usb *mctp_usb = netdev_priv(dev);
> +
> +	return mctp_usb_rx_queue(mctp_usb);

This will needlessly use GFP_ATOMIC

> +}

[..]

> +static int mctp_usb_probe(struct usb_interface *intf,
> +			  const struct usb_device_id *id)
> +{
> +	struct usb_endpoint_descriptor *ep_in, *ep_out;
> +	struct usb_host_interface *iface_desc;
> +	struct net_device *netdev;
> +	struct mctp_usb *dev;
> +	int rc;
> +
> +	/* only one alternate */
> +	iface_desc = intf->cur_altsetting;
> +
> +	rc = usb_find_common_endpoints(iface_desc, &ep_in, &ep_out, NULL, NULL);
> +	if (rc) {
> +		dev_err(&intf->dev, "invalid endpoints on device?\n");
> +		return rc;
> +	}
> +
> +	netdev = alloc_netdev(sizeof(*dev), "mctpusb%d", NET_NAME_ENUM,
> +			      mctp_usb_netdev_setup);
> +	if (!netdev)
> +		return -ENOMEM;
> +
> +	SET_NETDEV_DEV(netdev, &intf->dev);
> +	dev = netdev_priv(netdev);
> +	dev->netdev = netdev;
> +	dev->usbdev = usb_get_dev(interface_to_usbdev(intf));

Taking a reference.
Where is the corresponding put?

> +	dev->intf = intf;
> +	usb_set_intfdata(intf, dev);
> +
> +	dev->ep_in = ep_in->bEndpointAddress;
> +	dev->ep_out = ep_out->bEndpointAddress;
> +
> +	dev->tx_urb = usb_alloc_urb(0, GFP_KERNEL);
> +	dev->rx_urb = usb_alloc_urb(0, GFP_KERNEL);
> +	if (!dev->tx_urb || !dev->rx_urb) {
> +		rc = -ENOMEM;
> +		goto err_free_urbs;
> +	}
> +
> +	rc = register_netdev(netdev);
> +	if (rc)
> +		goto err_free_urbs;
> +
> +	return 0;
> +
> +err_free_urbs:
> +	usb_free_urb(dev->tx_urb);
> +	usb_free_urb(dev->rx_urb);
> +	free_netdev(netdev);
> +	return rc;
> +}