[PATCH net-next v4 4/6] net: qualcomm: rmnet: use masks instead of C bit-fields
From: Alex Elder <hidden>
Date: 2021-03-15 13:35:47
Also in:
lkml
Subsystem:
networking drivers, qualcomm rmnet driver, the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Subash Abhinov Kasiviswanathan, Sean Tranchetti, Linus Torvalds
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, and define a single-byte flags
field instead. Define a mask for the single bit "command" flag,
and another mask for the encoded pad length. The content of both
fields can be accessed using a simple bitwise AND operation.
Signed-off-by: Alex Elder <redacted>
Reviewed-by: Bjorn Andersson <redacted>
---
v4: - Don't use u8_get_bits() to access the pad length
- Added BUILD_BUG_ON() to ensure field width is adequate
v3: - Use BIT(x) and don't use u8_get_bits() for the command flag
.../ethernet/qualcomm/rmnet/rmnet_handlers.c | 4 ++--
.../ethernet/qualcomm/rmnet/rmnet_map_data.c | 4 +++-
include/linux/if_rmnet.h | 23 ++++++++-----------
3 files changed, 15 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..0be5ac7ab2617 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c@@ -61,7 +61,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb, u16 len, pad; u8 mux_id; - if (map_header->cd_bit) { + if (map_header->flags & MAP_CMD_FLAG) { /* Packet contains a MAP command (not data) */ if (port->data_format & RMNET_FLAGS_INGRESS_MAP_COMMANDS) return rmnet_map_command(skb, port);
@@ -70,7 +70,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb, } mux_id = map_header->mux_id; - pad = map_header->pad_len; + pad = map_header->flags & MAP_PAD_LEN_MASK; 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..3c3307949db00 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c@@ -286,6 +286,7 @@ struct rmnet_map_header *rmnet_map_add_map_header(struct sk_buff *skb, return map_header; } + BUILD_BUG_ON(MAP_PAD_LEN_MASK < 3); padding = ALIGN(map_datalen, 4) - map_datalen; if (padding == 0)
@@ -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 = padding & MAP_PAD_LEN_MASK; return map_header; }
diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index 8c7845baf3837..a02f0a3df1d9a 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_CMD_FLAG, MAP_PAD_LEN_MASK */ + u8 mux_id; + __be16 pkt_len; /* Length of packet, including pad */ } __aligned(1); +/* rmnet_map_header flags field: + * PAD_LEN: number of pad bytes following packet data + * CMD: 1 = packet contains a MAP command; 0 = packet contains data + */ +#define MAP_PAD_LEN_MASK GENMASK(5, 0) +#define MAP_CMD_FLAG BIT(7) + struct rmnet_map_dl_csum_trailer { u8 reserved1; #if defined(__LITTLE_ENDIAN_BITFIELD)
--
2.27.0