On Thu 04 Mar 16:34 CST 2021, Alex Elder wrote:
> The actual layout of bits defined in C bit-fields (e.g. int foo : 3)
> is implementation-defined. Structures defined in <linux/if_rmnet.h>
> address this by specifying all bit-fields twice, to cover two
> possible layouts.
>
> I think this pattern is repetitive and noisy, and I find the whole
> notion of compiler "bitfield endianness" to be non-intuitive.
>
> Stop using C bit-fields for the command/data flag and the pad length
> fields in the rmnet_map structure. Instead, define a single-byte
> flags field, and use the functions defined in <linux/bitfield.h>,
> along with field mask constants to extract or assign values within
> that field.
>
Reviewed-by: Bjorn Andersson <bjorn.anders...@linaro.org>
Regards,
Bjorn
> Signed-off-by: Alex Elder <el...@linaro.org>
> ---
> .../ethernet/qualcomm/rmnet/rmnet_handlers.c | 5 ++--
> .../ethernet/qualcomm/rmnet/rmnet_map_data.c | 4 +++-
> include/linux/if_rmnet.h | 23 ++++++++-----------
> 3 files changed, 16 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> index 2a6b2a609884c..30f8e2f02696b 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> @@ -4,6 +4,7 @@
> * RMNET Data ingress/egress handler
> */
>
> +#include <linux/bitfield.h>
> #include <linux/netdevice.h>
> #include <linux/netdev_features.h>
> #include <linux/if_arp.h>
> @@ -61,7 +62,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,
> u16 len, pad;
> u8 mux_id;
>
> - if (map_header->cd_bit) {
> + if (u8_get_bits(map_header->flags, MAP_CMD_FMASK)) {
> /* Packet contains a MAP command (not data) */
> if (port->data_format & RMNET_FLAGS_INGRESS_MAP_COMMANDS)
> return rmnet_map_command(skb, port);
> @@ -70,7 +71,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,
> }
>
> mux_id = map_header->mux_id;
> - pad = map_header->pad_len;
> + pad = u8_get_bits(map_header->flags, MAP_PAD_LEN_FMASK);
> len = ntohs(map_header->pkt_len) - pad;
>
> if (mux_id >= RMNET_MAX_LOGICAL_EP)
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index fd55269c2ce3c..3291f252d81b0 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -4,6 +4,7 @@
> * RMNET Data MAP protocol
> */
>
> +#include <linux/bitfield.h>
> #include <linux/netdevice.h>
> #include <linux/ip.h>
> #include <linux/ipv6.h>
> @@ -299,7 +300,8 @@ struct rmnet_map_header *rmnet_map_add_map_header(struct
> sk_buff *skb,
>
> done:
> map_header->pkt_len = htons(map_datalen + padding);
> - map_header->pad_len = padding & 0x3F;
> + /* This is a data packet, so the CMD bit is 0 */
> + map_header->flags = u8_encode_bits(padding, MAP_PAD_LEN_FMASK);
>
> return map_header;
> }
> diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
> index 8c7845baf3837..4824c6328a82c 100644
> --- a/include/linux/if_rmnet.h
> +++ b/include/linux/if_rmnet.h
> @@ -6,21 +6,18 @@
> #define _LINUX_IF_RMNET_H_
>
> struct rmnet_map_header {
> -#if defined(__LITTLE_ENDIAN_BITFIELD)
> - u8 pad_len:6;
> - u8 reserved_bit:1;
> - u8 cd_bit:1;
> -#elif defined (__BIG_ENDIAN_BITFIELD)
> - u8 cd_bit:1;
> - u8 reserved_bit:1;
> - u8 pad_len:6;
> -#else
> -#error "Please fix <asm/byteorder.h>"
> -#endif
> - u8 mux_id;
> - __be16 pkt_len;
> + u8 flags; /* MAP_*_FMASK */
> + u8 mux_id;
> + __be16 pkt_len; /* Length of packet, including pad */
> } __aligned(1);
>
> +/* rmnet_map_header flags field:
> + * CMD: 1 = packet contains a MAP command; 0 = packet contains data
> + * PAD_LEN: number of pad bytes following packet data
> + */
> +#define MAP_CMD_FMASK GENMASK(7, 7)
> +#define MAP_PAD_LEN_FMASK GENMASK(5, 0)
> +
> struct rmnet_map_dl_csum_trailer {
> u8 reserved1;
> #if defined(__LITTLE_ENDIAN_BITFIELD)
> --
> 2.20.1
>
