iptfs_drop_timer(9)

✨ iptfs_drop_timer — a kernel API manual, but make it make sense ✨

okay so bestie, this one's from the Kernel API Manual, section 9 (that's the kernel-functions girlies 💅). Sit down, hydrate, and let's get into it 🫶

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💖 NAME 💖

iptfs_drop_timer — literally just handles drop timer expiry. That's the whole job. She's the one who shows up when the timer goes off ⏰

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🌸 SYNOPSIS 🌸

enum hrtimer_restart iptfs_drop_timer (struct hrtimer *me );

yes it returns an enum hrtimer_restart, and yes the parameter is just called me. main character energy fr fr 👑

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🎀 ARGUMENTS 🎀

• me — the timer. that's it. that's the argument. she's just out here being a timer 🕰️

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🦋 DESCRIPTION 🦋

So this is similar to our input function, iykyk — same vibe, different circumstances ✨

The drop timer gets set in two situations, and you need to know both:

• when we start an in progress reassembly, and
• when we save a future packet in the window saved array

NOTE 📌 packets in the save window are always newer WRT drop times as they get further in the future. Like, for real, check it:

if slots (S0, S1, ... Sn) and Dn is the drop time for slot Sn, then D(n-1) <= D(n).

So the drop times only ever go up as you walk the slots — no weird time-travel nonsense, ever 🧚

Which means... regardless of why the timer is firing, we can always discard any inprogress fragment. Always. And here's the reasoning, because she's not just being chaotic:

• either it's the reassembly timer, or
• slot 0 is going to be dropped, because S0 must have the most recent drop time, and slot 0 holds the continuation fragment of the in progress packet

Basically slot 0 is the one holding the bag, so she's packing up either way 💀

Returns HRTIMER_NORESTART. No restart, bestie. She does her thing and she's out 🌈

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👑 SEE ALSO 👑

okay this list is LONG, so buckle up. Kernel file ./net/xfrm/xfrm_iptfs.c, plus the whole friend group:

• IPTFS_DEFAULT_DROP_TIME_USECS(9)
• IPTFS_DEFAULT_REORDER_WINDOW(9)
• IPTFS_DEFAULT_INIT_DELAY_USECS(9)
• IPTFS_DEFAULT_MAX_QUEUE_SIZE(9)
• struct xfrm_iptfs_config(9)
• struct xfrm_iptfs_data(9)
• iptfs_alloc_skb(9)
• iptfs_skb_head_to_frag(9)
• struct iptfs_skb_frag_walk(9)
• iptfs_skb_prepare_frag_walk(9)
• iptfs_skb_can_add_frags(9)
• iptfs_skb_add_frags(9)
• iptfs_pskb_add_frags(9)
• iptfs_pskb_extract_seq(9)
• iptfs_input_save_runt(9)
• __iptfs_iphlen(9)
• __iptfs_iplen(9)
• iptfs_complete_inner_skb(9)
• iptfs_reassem_abort(9)
• iptfs_reassem_done(9)
• iptfs_reassem_cont(9)
• iptfs_input_ordered(9)
• iptfs_input(9)
• iptfs_enqueue(9)
• iptfs_copy_create_frag(9)
• iptfs_copy_create_frags(9)
• iptfs_first_skb(9)
• iptfs_encap_add_ipv4(9)
• iptfs_encap_add_ipv6(9)
• iptfs_prepare_output(9)
• __iptfs_get_inner_mtu(9)
• iptfs_get_inner_mtu(9)
• iptfs_user_init(9)

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and that's the page, babes 🍓 this one lives in ./net/xfrm and is dated October 2026 — yes, the future, we're ahead of schedule 💜 mwah, go read your man pages 💅