Re: [RFC PATCH net-next v6 05/15] netdev: support binding dma-buf to netdevice

On Mon,  4 Mar 2024 18:01:40 -0800 Mina Almasry wrote:

+	if (!dev || !dev->netdev_ops)
+		return -EINVAL;

too defensive

+	if (!dev->netdev_ops->ndo_queue_stop ||
+	    !dev->netdev_ops->ndo_queue_mem_free ||
+	    !dev->netdev_ops->ndo_queue_mem_alloc ||
+	    !dev->netdev_ops->ndo_queue_start)
+		return -EOPNOTSUPP;
+
+	new_mem = dev->netdev_ops->ndo_queue_mem_alloc(dev, rxq_idx);
+	if (!new_mem)
+		return -ENOMEM;
+
+	err = dev->netdev_ops->ndo_queue_stop(dev, rxq_idx, &old_mem);
+	if (err)
+		goto err_free_new_mem;
+
+	err = dev->netdev_ops->ndo_queue_start(dev, rxq_idx, new_mem);
+	if (err)
+		goto err_start_queue;
+
+	dev->netdev_ops->ndo_queue_mem_free(dev, old_mem);

nice :)

+	rxq = __netif_get_rx_queue(dev, rxq_idx);
+
+	if (rxq->binding)

nit: a few places have an empty line between call and error check

+		return -EEXIST;

+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;

this can be a flag on the netlink policy, no?

	flags: [ admin-perm ]

on the op

+	dmabuf = dma_buf_get(dmabuf_fd);
+	if (IS_ERR_OR_NULL(dmabuf))
+		return -EBADFD;

+	hdr = genlmsg_put(rsp, info->snd_portid, info->snd_seq,

genlmsg_iput()

+static int netdev_netlink_notify(struct notifier_block *nb, unsigned long state,
+				 void *_notify)
+{
+	struct netlink_notify *notify = _notify;
+	struct netdev_dmabuf_binding *rbinding;
+
+	if (state != NETLINK_URELEASE || notify->protocol != NETLINK_GENERIC)
+		return NOTIFY_DONE;
+
+	rtnl_lock();
+
+	list_for_each_entry(rbinding, &netdev_rbinding_list, list) {
+		if (rbinding->owner_nlportid == notify->portid) {
+			netdev_unbind_dmabuf(rbinding);
+			break;
+		}
+	}
+
+	rtnl_unlock();
+
+	return NOTIFY_OK;
+}

While you were not looking we added three new members to the netlink
family:

 * @sock_priv_size: the size of per-socket private memory
 * @sock_priv_init: the per-socket private memory initializer
 * @sock_priv_destroy: the per-socket private memory destructor

You should be able to associate state with a netlink socket
and have it auto-destroyed if the socket closes.
LMK if that doesn't work for you, I was hoping it would fit nicely.

I just realized now that the code gen doesn't know how to spit
those members out, but I'll send a patch tomorrow, you can hack
it manually until that gets in.