[PATCH] common/mlx5: fix mac deletion on Linux

[Dariusz Sosnowski]

On Wed, Mar 18, 2026 at 05:36:28PM +0100, David Marchand wrote:
> Re-enable debug logs unconditionally, this helps understanding why mac
> deletions were silently failing (while a bridge fdb del command was
> working fine).
> 
> testpmd> mac_addr add 0 FA:35:44:3F:58:31
> testpmd> mac_addr remove 0 FA:35:44:3F:58:31
> mlx5_common: Interface 35 cannot remove MAC address FA:35:44:3F:58:31
> 	Operation not supported
> 
> Then, fix mac deletion as the NLM_F_CREATE == 0x200 flag is relevant
> with a RTM_NEWNEIGH op.
> For a RTM_DELNEIGH op, 0x200 == NLM_F_BULK and passing this flag
> makes the deletion fail miserably for a single mac.
> 
> Fixes: ccdcba53a3f4 ("net/mlx5: use Netlink to add/remove MAC addresses")
> Cc: stable at dpdk.org
> 
> Signed-off-by: David Marchand <david.marchand at redhat.com>
> ---
>  drivers/common/mlx5/linux/mlx5_nl.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/common/mlx5/linux/mlx5_nl.c b/drivers/common/mlx5/linux/mlx5_nl.c
> index eceb3d796f..b50431fb61 100644
> --- a/drivers/common/mlx5/linux/mlx5_nl.c
> +++ b/drivers/common/mlx5/linux/mlx5_nl.c
> @@ -581,8 +581,8 @@ mlx5_nl_mac_addr_modify(int nlsk_fd, unsigned int iface_idx,
>  	} req = {
>  		.hdr = {
>  			.nlmsg_len = NLMSG_LENGTH(sizeof(struct ndmsg)),
> -			.nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE |
> -				NLM_F_EXCL | NLM_F_ACK,
> +			.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK |
> +				add ? NLM_F_CREATE | NLM_F_EXCL : 0,

It seems that this expression is constructed incorrectly.
IIUC this will be "parenthesised" as follows:

	((NLM_F_REQUEST | NLM_F_ACK) | add) ? (NLM_F_CREATE | NLM_F_EXCL) : 0

Since bitwise OR has higher precendence.
So "add" value will be ignored and only "NLM_F_CREATE | NLM_F_EXCL"
will be returned.

Could you please add parenthesis around the ternary?

>  			.nlmsg_type = add ? RTM_NEWNEIGH : RTM_DELNEIGH,
>  		},
>  		.ndm = {
> @@ -612,7 +612,6 @@ mlx5_nl_mac_addr_modify(int nlsk_fd, unsigned int iface_idx,
>  		goto error;
>  	return 0;
>  error:
> -#ifdef RTE_PMD_MLX5_DEBUG
>  	{
>  		char m[RTE_ETHER_ADDR_FMT_SIZE];
>  
> @@ -622,7 +621,6 @@ mlx5_nl_mac_addr_modify(int nlsk_fd, unsigned int iface_idx,
>  			iface_idx,
>  			add ? "add" : "remove", m, strerror(rte_errno));
>  	}
> -#endif
>  	return -rte_errno;
>  }
>  

Best regards,
Dariusz Sosnowski