netdev - Re: [PATCH net v2 1/1] i40e: Fix the inability to attach XDP program on downed interface

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Date:   Wed, 7 Dec 2022 10:25:44 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     Tony Nguyen <anthony.l.nguyen@...el.com>
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com,
        Bartosz Staszewski <bartoszx.staszewski@...el.com>,
        netdev@...r.kernel.org, bjorn@...nel.org,
        maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
        ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
        john.fastabend@...il.com, bpf@...r.kernel.org,
        Mateusz Palczewski <mateusz.palczewski@...el.com>,
        Shwetha Nagaraju <Shwetha.nagaraju@...el.com>
Subject: Re: [PATCH net v2 1/1] i40e: Fix the inability to attach XDP program
 on downed interface

On 07 Dec 10:08, Tony Nguyen wrote:
>From: Bartosz Staszewski <bartoszx.staszewski@...el.com>
>
>Whenever trying to load XDP prog on downed interface, function i40e_xdp
>was passing vsi->rx_buf_len field to i40e_xdp_setup() which was equal 0.
>i40e_open() calls i40e_vsi_configure_rx() which configures that field,
>but that only happens when interface is up. When it is down, i40e_open()
>is not being called, thus vsi->rx_buf_len is not set.
>
>Solution for this is calculate buffer length in newly created
>function - i40e_calculate_vsi_rx_buf_len() that return actual buffer
>length. Buffer length is being calculated based on the same rules
>applied previously in i40e_vsi_configure_rx() function.
>
>Fixes: 613142b0bb88 ("i40e: Log error for oversized MTU on device")
>Fixes: 0c8493d90b6b ("i40e: add XDP support for pass and drop actions")
>Signed-off-by: Bartosz Staszewski <bartoszx.staszewski@...el.com>
>Signed-off-by: Mateusz Palczewski <mateusz.palczewski@...el.com>
>Tested-by: Shwetha Nagaraju <Shwetha.nagaraju@...el.com>
>Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
>Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
>---
>v2:
>- Change title and rework commit message
>- Dropped, previous, patch 1
>
>v1: https://lore.kernel.org/netdev/20221115000324.3040207-1-anthony.l.nguyen@intel.com/
>
> drivers/net/ethernet/intel/i40e/i40e_main.c | 42 +++++++++++++++------
> 1 file changed, 30 insertions(+), 12 deletions(-)
>
>diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
>index 6416322d7c18..b8a8098110eb 100644
>--- a/drivers/net/ethernet/intel/i40e/i40e_main.c
>+++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
>@@ -3693,6 +3693,30 @@ static int i40e_vsi_configure_tx(struct i40e_vsi *vsi)
> 	return err;
> }
>
>+/**
>+ * i40e_calculate_vsi_rx_buf_len - Calculates buffer length
>+ *
>+ * @vsi: VSI to calculate rx_buf_len from
>+ */
>+static u16 i40e_calculate_vsi_rx_buf_len(struct i40e_vsi *vsi)
>+{
>+	u16 ret;
>+
>+	if (!vsi->netdev || (vsi->back->flags & I40E_FLAG_LEGACY_RX)) {
>+		ret = I40E_RXBUFFER_2048;
>+#if (PAGE_SIZE < 8192)
>+	} else if (!I40E_2K_TOO_SMALL_WITH_PADDING &&
>+		   (vsi->netdev->mtu <= ETH_DATA_LEN)) {
>+		ret = I40E_RXBUFFER_1536 - NET_IP_ALIGN;
>+#endif
>+	} else {
>+		ret = (PAGE_SIZE < 8192) ? I40E_RXBUFFER_3072 :
>+					   I40E_RXBUFFER_2048;
>+	}
>+
>+	return ret;
>+}

nit: linux coding style states:
"Do not unnecessarily use braces where a single statement will do"

I think this applies here.

Also you could simplify this function to do early returns and drop the u16
ret variable and all the else statements.

if (condition 1)
     return val1;

if (condition 2)
     return val2;

return val3;


Other than that LGTM.