kern_reserve_flow(9)

💅 kern_reserve_flow(9) — like, the flow-reserving girlie of the kernel API manual

okay so bestie, welcome to kern_reserve_flow(9) — yes that's the manual name, section 9, kernel API manual vibes, we're in the big leagues now 🎀. This is the page where the kernel gets a hardware flow reserved for itself, and honestly? it ate. let me walk you through it ✨

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🌸 NAME 🌸

kern_reserve_flow — allocate a hardware flow 🦋

like, that's literally the whole thing. allocate. a hardware. flow. periodt.

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✨ SYNOPSIS ✨

int kern_reserve_flow (struct hfi1_ctxtdata *rcd , int last );

that's the signature, copy it exactly bestie, no cap, don't be out here renaming anything 🙈

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🎀 ARGUMENTS 🎀

• rcd — the context you're using for the allocation, i.e. your struct hfi1_ctxtdata * moment. it's giving main character context energy 💜
• last — the index of the preferred flow, your little wishlist entry. and if you literally don't care? pass RXE_NUM_TID_FLOWS to signify "don't care" ✨ (yes that's the exact sentinel, write it down, iykyk)

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💖 DESCRIPTION 💖

so here's the tea: this function uses a bit mask based allocation to reserve a hardware flow for use in receiving KDETH data packets. cute, efficient, iconic. 🧚

and if you did specify a preferred flow (last, the little fave), the function will attempt to reserve that flow again — but only if it's available. if it's taken? tough luck babe, it moves on. 💀

⚠️ okay this part is important and i'm not gonna soften it: the exp_lock must be held. not optional. not a suggestion. hold the lock, bestie. 🔥

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⭐ RETURN ⭐

• On success: a positive value between 0 and RXE_NUM_TID_FLOWS - 1 🌈
• On failure: -EAGAIN 😭

that's it, that's the whole return contract, no surprises, we love a clear API 🫶

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🦋 SEE ALSO 🦋

okay this list is long and honestly kind of a flex, so let's go through it together 💅

• Kernel file ./drivers/infiniband/hw/hfi1/tid_rdma.c
• TID RDMA READ protocol(9)
• qp_to_rcd(9)
• lock ordering(9)
• kernel_tid_waiters(9)
• dequeue_tid_waiter(9)
• queue_qp_for_tid_wait(9)
• __trigger_tid_waiter(9)
• tid_rdma_schedule_tid_wakeup(9)
• tid_rdma_trigger_resume(9)
• tid_rdma_find_phys_blocks_4k(9)
• tid_flush_pages(9)
• tid_rdma_find_phys_blocks_8k(9)
• hfi1_kern_exp_rcv_setup(9)
• hfi1_kern_exp_rcv_free_flows(9)
• __trdma_clean_swqe(9)
• hfi1_schedule_tid_send(9)

go read them. all of them. you'll be smarter, i promise. 👑

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and that's the page, bestie!! 💖 this little beauty lives over in ./drivers/infiniband/hw/hfi1 and the version we're reading is dated October 2026 🌸 so like, fresh off the press fr fr. mwah, go reserve some flows, you've got this 🎀✨🦋