Re: [PATCH RFC v1 03/15] bnxt: add XDP frame size to driver

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On Tue, Mar 17, 2020 at 06:29:22PM +0100, Jesper Dangaard Brouer wrote:
> This driver uses full PAGE_SIZE pages when XDP is enabled.
> 
> Cc: Michael Chan <michael.chan@xxxxxxxxxxxx>
> Cc: Andy Gospodarek <andrew.gospodarek@xxxxxxxxxxxx>
> Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> ---
>  drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
> index c6f6f2033880..5e3b4a3b69ea 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
> @@ -138,6 +138,7 @@ bool bnxt_rx_xdp(struct bnxt *bp, struct bnxt_rx_ring_info *rxr, u16 cons,
>  	xdp_set_data_meta_invalid(&xdp);
>  	xdp.data_end = *data_ptr + *len;
>  	xdp.rxq = &rxr->xdp_rxq;
> +	xdp.frame_sz = PAGE_SIZE; /* BNXT_RX_PAGE_MODE(bp) when XDP enabled */

So if we want this to be the true size that the packet inside the the DMA
buffer could grow to, I _think_ this would need to be:

	xdp.frame_sz = PAGE_SIZE - XDP_PACKET_HEADROOM;

but I also noted that in patch 8 of the series that there is a check
against data_end - data_hard_start, so functionally your original patch
appears to be correct.

If the intent was just to capture the size of the [DMA] buffer available
for the datagram, maybe calling this new field 'buf_sz' or similar would
be nice as it does not convey anything about the on-wire size like
'frame_sz' does.


>  	orig_data = xdp.data;
>  
>  	rcu_read_lock();
> 
> 



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