ib_map_mr_sg(9)

💅 ib_map_mr_sg(9) — the Kernel API Manual glow-up 🎀

okay bestie, welcome to ib_map_mr_sg(9) from the Kernel API Manual ✨ this one's short but she's important — she maps stuff and sets stuff and honestly she ate 💅

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✨ NAME ✨

ib_map_mr_sg — maps the biggest prefix of a dma mapped SG list and then sets it on the memory region 🫶 like, she takes what she can get and commits to it, main character energy fr fr.

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🦋 SYNOPSIS 🦋

int ib_map_mr_sg (struct ib_mr *mr , struct scatterlist *sg , int
sg_nents , unsigned int *sg_offset , unsigned int page_size );

she returns an int, no cap 💖

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🌸 ARGUMENTS 🌸

• mr — the memory region 👑 that's the whole point of the vibe check
• sg — a dma mapped scatterlist 🦋
• sg_nents — how many entries live in sg, literally just the count bestie
• sg_offset — offset in bytes into sg, yes bytes, don't @ me
• page_size — the page vector desired page size 🎀 "desired" is doing a lot of work there iykyk

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💜 DESCRIPTION 💜

so there are constraints, and we respect them 😌✨ not me being obsessed with rules but like, here they are:

• 🫶 the first sg element is allowed to have an offset. she gets a little grace period, we love that for her
• 💅 each sg element must either be aligned to page_size or be virtually contiguous to the previous element. and if an sg element has a non-contiguous offset — the mapping prefix will not include it 🚫 that one's not invited to the party
• 🎀 the last sg element is allowed to have a length less than page_size (short king behavior, iconic)
• ⭐ if sg_nents total byte length exceeds the mr max_num_sge * page_size then only max_num_sg entries will be mapped. that's the cap bestie, that's the limit
• 🔥 if the MR was allocated with type IB_MR_TYPE_SG_GAPS, none of these constraints hold and the page_size argument is ignored 😭 literally ghosted

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🌈 what she gives back

Returns the number of sg elements that were mapped to the memory region 💖 count them, love them.

after this completes successfully, the memory region is ready for registration 👑 like she's all dressed up and ready to go out. but successfully is doing heavy lifting — don't skip that word 🙈

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🧚 SEE ALSO 🧚

the whole friend group showed up, no gatekeeping here:

Kernel file ./drivers/infiniband/core/verbs.c, __ib_alloc_pd(9), ib_dealloc_pd_user(9), rdma_copy_ah_attr(9), rdma_replace_ah_attr(9), rdma_move_ah_attr(9), rdma_create_ah(9), rdma_create_user_ah(9), rdma_move_grh_sgid_attr(9), rdma_destroy_ah_attr(9), ib_create_srq_user(9), ib_create_qp_user(9), ib_resolve_eth_dmac(9), ib_modify_qp_with_udata(9), ib_alloc_mr(9), ib_alloc_mr_integrity(9), ib_alloc_xrcd_user(9), ib_dealloc_xrcd_user(9), ib_create_wq(9), ib_destroy_wq_user(9), ib_map_mr_sg_pi(9), ib_sg_to_pages(9), ib_drain_sq(9), ib_drain_rq(9), ib_drain_qp(9), rdma_alloc_hw_stats_struct(9), rdma_free_hw_stats_struct(9)

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okay that's the whole page, mwah 💋

🌸 from the ./drivers/infiniband/core girlies, dated October 2026, page ib_map_mr_sg(9) — stay hydrated, read your manpages, and never, ever forget that page_size is ignored for IB_MR_TYPE_SG_GAPS 💖✨🎀