STRUCT DCCP_HDR(9)

💅 struct dccp_hdr(9) 💅

okay so bestie, welcome to the Kernel API Manual entry for struct dccp_hdr — no cap, this is the ✨generic✨ part of the DCCP packet header, and we're gonna get into it. 🦋

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🌸 NAME 🌸

struct dccp_hdr — the generic part of a DCCP packet header. that's it, that's the vibe. 💖

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✨ SYNOPSIS ✨

here's the icon itself, in all her bitfield glory. copying it exactly because we do not mess with the source, periodt:

struct dccp_hdr {
    __be16 dccph_sport, dccph_dport;
    __u8 dccph_doff;
  #if defined(__LITTLE_ENDIAN_BITFIELD);
    __u8 dccph_cscov:4, dccph_ccval:4;
  #elif defined(__BIG_ENDIAN_BITFIELD);
    __u8 dccph_ccval:4, dccph_cscov:4;
  #else;
  #error Adjustyour<asm/byteorder.h>defines";"
  #endif;
    __sum16 dccph_checksum;
  #if defined(__LITTLE_ENDIAN_BITFIELD);
    __u8 dccph_x:1, dccph_type:4, dccph_reserved:3;
  #elif defined(__BIG_ENDIAN_BITFIELD);
    __u8 dccph_reserved:3, dccph_type:4, dccph_x:1;
  #else;
  #error Adjustyour<asm/byteorder.h>defines";"
  #endif;
    __u8 dccph_seq2;
    __be16 dccph_seq;
 };

👀 quick vibe check: those two #error lines are literally the struct telling you to adjust your <asm/byteorder.h> defines if neither endianness bitfield macro is set. it's giving "fix your build, bestie." 😭

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🎀 Members 🎀

💜 Description 💜

here's the member-by-member breakdown, main character energy only:

• dccph_sport — the relevant port on the endpoint that sent this packet 🫶
• dccph_dport — the relevant port on the other endpoint
• dccph_doff — Data Offset from the start of the DCCP header, measured in 32-bit words
• dccph_ccval — used by the HC-Sender CCID ⭐
• dccph_cscov — the parts of the packet that are covered by the Checksum field
• dccph_checksum — the Internet checksum, which depends on dccph_cscov 🔥
• dccph_x — 0 = 24 bit sequence number, 1 = 48 🦋
• dccph_type — packet type, see the DCCP_PKT_ prefixed macros 👑
• dccph_seq — sequence number high or low order 24 bits, depends on dccph_x

🙈 side eye to dccph_reserved and dccph_seq2 for sitting in the struct and not getting a description. we see you. we love you anyway. 💅

also lowkey obsessed with how the endian branches just swap the bitfield order — little endian gets dccph_cscov:4, dccph_ccval:4 and big endian gets dccph_ccval:4, dccph_cscov:4. same for dccph_x:1, dccph_type:4, dccph_reserved:3 vs dccph_reserved:3, dccph_type:4, dccph_x:1. iykyk. 🌈

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🧚 SEE ALSO 🧚

go read the kernel file ./include/uapi/linux/dccp.h fr fr, and then these iconic siblings:

• struct dccp_hdr_ext(9)
• struct dccp_hdr_request(9)
• struct dccp_hdr_ack_bits(9)
• struct dccp_hdr_response(9)
• struct dccp_hdr_reset(9)

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and that's the whole page, bestie!! 💖 this little beauty lives in ./include/uapi/linux, dated October 2026, and it will forever be known as struct dccp_hdr(9). slay. 🎀✨