crush_do_rule(9)

✨ crush_do_rule(9) ✨

okay so bestie, you've wandered into the Kernel API Manual 💅 and this page is genuinely iconic — it's crush_do_rule(9), the actual kernel-side baddie that does the math. sit down, hydrate, let's get into it 🫶

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🌸 NAME 🌸

crush_do_rule — calculate a mapping with the given input and rule

like, that's the whole vibe: you hand it an input and a rule, and it goes and computes you a mapping. no cap, that's the job. 👑

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🦋 SYNOPSIS 🦋

int crush_do_rule (const struct crush_map *map , int ruleno , int x ,
int *result , int result_max , const __u32 *weight , int weight_max ,
void *cwin , const struct crush_choose_arg *choose_args );

yes she takes nine arguments and yes she's highkey living her main character era. type it exactly like that, ok? 🔥

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🎀 ARGUMENTS 🎀

okay so here's the cast of characters, going one by one, no skipping, periodt:

• map — the crush_map. literally the map. it's giving "the whole world, in struct form." 🌈
• ruleno — the rule id. which rule are we running? that's the number, bestie, you pick it. 💅
• x — hash input. this is the thing getting hashed. it's the seed of the whole situation. ✨
• result — pointer to result vector. this is where the output lands. the Cinderella slipper of the function, if you will. 🎀
• result_max — maximum result size. the capacity, the limit, the "know your lane" of the result vector. 🦋
• weight — weight vector (for map leaves). leaves only, iykyk. 🍓
• weight_max — size of weight vector. because a vector without a size is just chaos, and not the fun kind. 😭
• cwin — pointer to at least crush_work_size bytes of memory. at least, bestie — don't be out here handing it 12 bytes and hoping for the best. 🙈
• choose_args — weights and ids for each known bucket. buckets get their own little weights-and-ids moment, and this is it. 🧚

ngl, that cwin one is the classic "must be big enough" situation — the page says at least crush_work_size bytes, so take that literally, fr fr. 💀

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👑 SEE ALSO 👑

if you're nosy (we love a curious queen), go look at:

• Kernel file ./net/ceph/crush/mapper.c
• crush_find_rule(9)
• crush_choose_firstn(9)

the whole friend group, together at last 🫶

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okay that's the whole page, you ate that 💖 also for the record this one's from ./net/ceph/crush, dated October 2026 — so mark your calendar and stan responsibly, bestie. slay! 🌟