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

On Tue, Mar 5, 2024, at 03:01, Mina Almasry wrote:

+int netdev_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,

•        struct netdev_dmabuf_binding **out)
  

+{

• struct netdev_dmabuf_binding *binding;
• static u32 id_alloc_next;
• struct scatterlist *sg;
• struct dma_buf *dmabuf;
• unsigned int sg_idx, i;
• unsigned long virtual;
• int err;
• if (!capable(CAP_NET_ADMIN))

• return -EPERM;
  

• dmabuf = dma_buf_get(dmabuf_fd);
• if (IS_ERR_OR_NULL(dmabuf))

• return -EBADFD;
  

You should never need to use IS_ERR_OR_NULL() for a properly defined kernel interface. This one should always return an error or a valid pointer, so don't check for NULL.

• binding->attachment = dma_buf_attach(binding->dmabuf, dev->dev.parent);
• if (IS_ERR(binding->attachment)) {

• err = PTR_ERR(binding->attachment);
  

• goto err_free_id;
  

• }
• binding->sgt =

• dma_buf_map_attachment(binding->attachment, DMA_BIDIRECTIONAL);
  

• if (IS_ERR(binding->sgt)) {

• err = PTR_ERR(binding->sgt);
  

• goto err_detach;
  

• }

Should there be a check to verify that this buffer is suitable for network data?

In general, dmabuf allows buffers that are uncached or reside in MMIO space of another device, but I think this would break when you get an skb with those buffers and try to parse the data inside of the kernel on architectures where MMIO space is not a normal pointer or unaligned access is disallowed on uncached data.

Arnd