blk_mq_add_to_batch(9)

💅 blk_mq_add_to_batch — Kernel API Manual, bestie edition 🎀

okay so picture this: you're in the kernel, the manual is blk_mq_add_to_batch(9), and it's giving very specific little helper energy. It does exactly one thing and it does it slayfully. Let's get into it ✨

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✨ NAME ✨

blk_mq_add_to_batch — add a request to the completion batch 🫶

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🌸 SYNOPSIS 🌸

bool blk_mq_add_to_batch (struct request *req , struct io_comp_batch
*iob , bool is_error , void (*complete)(struct io_comp_batch *) );

like yes, that's the whole signature, no cap. four things in, one bool out 💖

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🦋 ARGUMENTS 🦋

• req — the request you're adding to the batch. the main character, honestly 👑
• iob — the batch itself, aka where req is going. the group chat it's being added to 💬
• is_error — set this to true if the request failed with an error. be honest with me, bestie 🙈
• complete — the completion handler for the request. (the manpage literally spells it "completaion" and honestly? iconic. we keep the energy, we just don't keep the typo in the code 😭 the name is complete, always has been 💅)

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💀 DESCRIPTION 💀

okay so the tea: batched completions only work when there is no I/O error and no special ->end_io handler.

that's it. that's the whole rule. no exception, no loophole, fr fr. if there's an error, or if something's got a special ->end_io handler going on, batching is simply not the vibe and this function will not be your girl 🌈

lowkey important: this is a condition, not a suggestion. respect the ->end_io 🫶

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⭐ RETURN ⭐

• true when the request was added to the batch ✨
• otherwise false 💔

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🔥 SEE ALSO 🔥

the kernel file lives at ./include/linux/blk-mq.h — go read it, it's giving lore 📖

and then there's the whole friend group:

• enum blk_eh_timer_return(9)
• struct blk_mq_hw_ctx(9)
• struct blk_mq_queue_map(9)
• enum hctx_type(9)
• struct blk_mq_tag_set(9)
• struct blk_mq_queue_data(9)
• struct blk_mq_ops(9)
• blk_mq_rq_state(9)
• blk_mq_rq_from_pdu(9)
• blk_mq_rq_to_pdu(9)
• blk_rq_nr_bvec(9)
• blk_rq_passthrough_stats(9)

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and that's the whole page, bestie 🧚 this lil drop shipped straight outta ./include/linux in October 2026, and its official handle is blk_mq_add_to_batch(9) — memorize it, cite it, live it 💜