htb_classify(9)

📦 version 7.3.1, in nixpkgs unstable

💖 htb_classify(9) — the Kernel API Manual, bestie edition 🎀

okay so this is htb_classify, and yes it lives in the Kernel API Manual (section 9, kernel internals, iykyk). she's a little function with a big job and honestly? she ate. let's get into it ✨

🌸 NAME 🌸

htb_classify — classify a packet into class. that's it, that's the whole vibe check 💅

✨ SYNOPSIS ✨

struct htb_class * htb_classify (struct sk_buff *skb , struct Qdisc *sch
, int *qerr );

literally copy-pasted the signature exactly because we do not paraphrase code in this house 🫶

🦋 ARGUMENTS 🦋

  • skb — the socket buffer. the packet in question. the main character, lowkey 🎀
  • sch — the active queue discipline. like, the qdisc that's currently clocked in and working 🌸
  • qerr — pointer for returned status code. she writes back to you, that's the whole point 💅

🌈 DESCRIPTION 🌈

okay so here's the tea on what she returns, and it's giving three-outcome situation 😭

  • she returns NULL if the packet should be dropped. bye bestie 💀
  • she returns -1 if the packet should be passed directly thru
  • in all other cases, the leaf class is returned 👑

and how does she pick? so glad you asked 🧚

we allow direct class selection by classid in priority. so that's the first thing she checks, no cap ✨

then we examine filters in qdisc and in inner nodes (if a higher filter points to the inner node). like, she digs down the tree, she's thorough 🦋

if we end up with classid MAJOR:0, we enqueue the skb into a special internal fifo (direct). and these packets then go directly thru. no detours, periodt 🔥

if we still have no valid leaf, we try to use the MAJOR:default leaf. backup plan energy, we love her for it 💜

and if it's still unsuccessful — then we finish and return the direct queue. that's the last resort and honestly she tried her best 😭

ngl the whole thing is a cascade of "try this, then this, then this" so if you're debugging and confused, you're not alone — just walk the order in the same sequence she does 💖

⭐ SEE ALSO ⭐

kernel file ./net/sched/sch_htb.c, plus the whole squad — go read these, they're iconic 👑:

and that's the page, bestie 🎀 she ships out of ./net/sched and the version stamp on this one is October 2026 — go forth, classify some packets, and slay 💅✨🦋
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