netdev - Re: [Intel-wired-lan] [PATCH iwl-net] ice: change q_index variable type to s16 to store -1 value

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Message-ID: <20241102143818.GM1838431@kernel.org>
Date: Sat, 2 Nov 2024 14:38:18 +0000
From: Simon Horman <horms@...nel.org>
To: Mateusz Polchlopek <mateusz.polchlopek@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, david.m.ertman@...el.com,
	netdev@...r.kernel.org,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-net] ice: change q_index variable
 type to s16 to store -1 value

On Mon, Oct 28, 2024 at 12:59:22PM -0400, Mateusz Polchlopek wrote:
> Fix Flow Director not allowing to re-map traffic to 0th queue when action
> is configured to drop (and vice versa).
> 
> The current implementation of ethtool callback in the ice driver forbids
> change Flow Director action from 0 to -1 and from -1 to 0 with an error,
> e.g:
> 
>  # ethtool -U eth2 flow-type tcp4 src-ip 1.1.1.1 loc 1 action 0
>  # ethtool -U eth2 flow-type tcp4 src-ip 1.1.1.1 loc 1 action -1
>  rmgr: Cannot insert RX class rule: Invalid argument
> 
> We set the value of `u16 q_index = 0` at the beginning of the function
> ice_set_fdir_input_set(). In case of "drop traffic" action (which is
> equal to -1 in ethtool) we store the 0 value. Later, when want to change
> traffic rule to redirect to queue with index 0 it returns an error
> caused by duplicate found.
> 
> Fix this behaviour by change of the type of field `q_index` from u16 to s16
> in `struct ice_fdir_fltr`. This allows to store -1 in the field in case
> of "drop traffic" action. What is more, change the variable type in the
> function ice_set_fdir_input_set() and assign at the beginning the new
> `#define ICE_FDIR_NO_QUEUE_IDX` which is -1. Later, if the action is set
> to another value (point specific queue index) the variable value is
> overwritten in the function.
> 
> Fixes: cac2a27cd9ab ("ice: Support IPv4 Flow Director filters")
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
> Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@...el.com>

This looks good, although I am interested to know what the maximum value
for q_index is. And, considering unsigned values are used elsewhere, if
using 0xffff within this driver was considered instead of -1.

That notwithstanding,

Reviewed-by: Simon Horman <horms@...nel.org>