Subject: Re: [RFC PATCH v2 02/11] netdev: implement netlink api to bind dma-buf to netdevice

From: Leon Romanovsky <[email-masked]>
Date: Sun, 13 Aug 2023 14:26:50 +0300

On Wed, Aug 09, 2023 at 06:57:38PM -0700, Mina Almasry wrote:
> Add a netdev_dmabuf_binding struct which represents the
> dma-buf-to-netdevice binding. The netlink API will bind the dma-buf to
> an rx queue on the netdevice. On the binding, the dma_buf_attach
> & dma_buf_map_attachment will occur. The entries in the sg_table from
> mapping will be inserted into a genpool to make it ready
> for allocation.
> 
> The chunks in the genpool are owned by a dmabuf_chunk_owner struct which
> holds the dma-buf offset of the base of the chunk and the dma_addr of
> the chunk. Both are needed to use allocations that come from this chunk.
> 
> We create a new type that represents an allocation from the genpool:
> page_pool_iov. We setup the page_pool_iov allocation size in the
> genpool to PAGE_SIZE for simplicity: to match the PAGE_SIZE normally
> allocated by the page pool and given to the drivers.
> 
> The user can unbind the dmabuf from the netdevice by closing the netlink
> socket that established the binding. We do this so that the binding is
> automatically unbound even if the userspace process crashes.
> 
> The binding and unbinding leaves an indicator in struct netdev_rx_queue
> that the given queue is bound, but the binding doesn't take effect until
> the driver actually reconfigures its queues, and re-initializes its page
> pool. This issue/weirdness is highlighted in the memory provider
> proposal[1], and I'm hoping that some generic solution for all
> memory providers will be discussed; this patch doesn't address that
> weirdness again.
> 
> The netdev_dmabuf_binding struct is refcounted, and releases its
> resources only when all the refs are released.
> 
> [1] https://lore.kernel.org/netdev/[email-masked]/
> 
> Signed-off-by: Willem de Bruijn <[email-masked]>
> Signed-off-by: Kaiyuan Zhang <[email-masked]>
> 
> Signed-off-by: Mina Almasry <[email-masked]>
> ---
>  include/linux/netdevice.h |  57 ++++++++++++
>  include/net/page_pool.h   |  27 ++++++
>  net/core/dev.c            | 178 ++++++++++++++++++++++++++++++++++++++
>  net/core/netdev-genl.c    | 101 ++++++++++++++++++++-
>  4 files changed, 361 insertions(+), 2 deletions(-)

<...>

> +void __netdev_devmem_binding_free(struct netdev_dmabuf_binding *binding);
> +
> +static inline void
> +netdev_devmem_binding_get(struct netdev_dmabuf_binding *binding)
> +{
> +	refcount_inc(&binding->ref);
> +}
> +
> +static inline void
> +netdev_devmem_binding_put(struct netdev_dmabuf_binding *binding)
> +{
> +	if (!refcount_dec_and_test(&binding->ref))
> +		return;
> +
> +	__netdev_devmem_binding_free(binding);
> +}

Not a big deal, but it looks like reimplemented version of kref_get/kref_put to me.

Thanks