IBV_QUERY_COMP_CNTR_CAPS(3)

💅 NAME 💅

okok so like — ibv_query_comp_cntr_caps — bestie this one queries completion counter capabilities. That's it, that's the whole gig ✨ (and yeah, this is the ibv_query_comp_cntr_caps(3) page from the Libibverbs Programmer's Manual, hi, welcome 🫶)

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🌸 SYNOPSIS 🌸

#include <infiniband/verbs.h>

int ibv_query_comp_cntr_caps(struct ibv_context *context,
                             struct ibv_comp_cntr_caps *caps);

literally just drop that include and you're in 🎀

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✨ DESCRIPTION ✨

okay so ibv_query_comp_cntr_caps() asks the RDMA device that's hanging out behind context all about its completion counter capabilities. it's giving "vibe check the hardware before you commit" energy, and honestly? obsessed 🔥

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🦋 ARGUMENTS 🦋

🎀 ibv_comp_cntr_caps

this is the struct you're filling up, and she's a whole personality:

struct ibv_comp_cntr_caps {
    uint64_t max_value;
    uint32_t max_counters;
    uint32_t supported_qp_attach_ops;
};

• max_value — the biggest number a completion counter can hold, no cap... well, actually yes cap 💀. if a subsequent increment would push past this value, the counter just wraps back around to zero. bye bestie 👋
• max_counters — the max number of completion counters you can create on this device. that's your limit, periodt.
• supported_qp_attach_ops — a bitmask of ibv_qp_attach_comp_cntr_op values, aka the receipts on which attach operations this device actually supports. the full list of operations lives over in ibv_qp_attach_comp_cntr(3) — go look, iykyk 👑

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💖 RETURN VALUE 💖

ibv_query_comp_cntr_caps() returns 0 on success 💚 or, if it's not feeling it, the value of errno on failure — and that value tells you why it flopped 😭

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💀 ERRORS 💀

• ENOTSUP — completion counters are simply not supported on this device. not her thing, not today, next question 🙈

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👑 SEE ALSO 👑

• ibv_create_comp_cntr(3)
• ibv_qp_attach_comp_cntr(3)

go read those too, they're the main characters of this friend group 🌈

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🧚 AUTHORS 🧚

Michael Margolin mrgolin@amazon.com — ty for the lore 🫶

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⭐ and that's the whole page!! brought to you by libibverbs, dated 2026-07-17, filing under ibv_query...cntr_caps(3) — slay, stay hydrated, read your manpages 💜✨🎀