Subject: Re: [PATCH net-next 5/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum trailer

From: Bjorn Andersson <[email-masked]>
Date: Thu, 4 Mar 2021 22:54:19 -0600

On Thu 04 Mar 16:34 CST 2021, Alex Elder wrote:

> Replace the use of C bit-fields in the rmnet_map_dl_csum_trailer
> structure with a single one-byte field, using constant field masks
> to encode or get at embedded values.
> 

Reviewed-by: Bjorn Andersson <[email-masked]>

Regards,
Bjorn

> Signed-off-by: Alex Elder <[email-masked]>
> ---
>  .../ethernet/qualcomm/rmnet/rmnet_map_data.c    |  2 +-
>  include/linux/if_rmnet.h                        | 17 +++++++----------
>  2 files changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 3291f252d81b0..29d485b868a65 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -365,7 +365,7 @@ int rmnet_map_checksum_downlink_packet(struct sk_buff *skb, u16 len)
>  
>  	csum_trailer = (struct rmnet_map_dl_csum_trailer *)(skb->data + len);
>  
> -	if (!csum_trailer->valid) {
> +	if (!u8_get_bits(csum_trailer->flags, MAP_CSUM_DL_VALID_FMASK)) {
>  		priv->stats.csum_valid_unset++;
>  		return -EINVAL;
>  	}
> diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
> index 4824c6328a82c..1fbb7531238b6 100644
> --- a/include/linux/if_rmnet.h
> +++ b/include/linux/if_rmnet.h
> @@ -19,21 +19,18 @@ struct rmnet_map_header {
>  #define MAP_PAD_LEN_FMASK		GENMASK(5, 0)
>  
>  struct rmnet_map_dl_csum_trailer {
> -	u8  reserved1;
> -#if defined(__LITTLE_ENDIAN_BITFIELD)
> -	u8  valid:1;
> -	u8  reserved2:7;
> -#elif defined (__BIG_ENDIAN_BITFIELD)
> -	u8  reserved2:7;
> -	u8  valid:1;
> -#else
> -#error	"Please fix <asm/byteorder.h>"
> -#endif
> +	u8 reserved1;
> +	u8 flags;			/* MAP_CSUM_DL_*_FMASK */
>  	__be16 csum_start_offset;
>  	__be16 csum_length;
>  	__be16 csum_value;
>  } __aligned(1);
>  
> +/* rmnet_map_dl_csum_trailer flags field:
> + *  VALID:	1 = checksum and length valid; 0 = ignore them
> + */
> +#define MAP_CSUM_DL_VALID_FMASK		GENMASK(0, 0)
> +
>  struct rmnet_map_ul_csum_header {
>  	__be16 csum_start_offset;
>  #if defined(__LITTLE_ENDIAN_BITFIELD)
> -- 
> 2.20.1
>