blk_mq_submit_bio(9)

💅 blk_mq_submit_bio(9) — the kernel API manual, bestie edition

Okay so bestie, welcome to the blk_mq_submit_bio(9) page ✨ — this is the kernel doc for the one function that takes your bio and actually yeets it toward a block device. Buckle up, it's short but it matters. 🫶

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🎀 SYNOPSIS

void blk_mq_submit_bio (struct bio *bio );

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🌸 ARGUMENTS

• bio — Bio pointer. That's it, that's the whole argument. One (1) pointer, and it's pointing at a bio. Iconic minimalism honestly. ✨

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💖 DESCRIPTION

So what it does: it builds up a request structure from q and bio, and sends it off to the device. Main character energy 🌈.

But — and this is the part where you need to pay attention, no cap — the request may not be queued directly to hardware if:

• This request can be merged with another one 👀
• We want to place request at plug queue for possible future merging 🧚
• There is an IO scheduler active at this queue 🦋

And like, it also will not queue the request if there is an error with the bio, or at the request creation. So if the bio's cooked, nothing goes anywhere. 💀

ngl the merge/plug/scheduler thing is lowkey the whole personality of this function — sometimes "submit" means "hand to hardware right now" and sometimes it absolutely does not. Read the three bullets, love them, memorize them. 💅

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👑 SEE ALSO

Kernel file ./block/blk-mq.c

• blk_mq_wait_quiesce_done(9)
• blk_mq_quiesce_queue(9)
• blk_update_request(9)
• blk_mq_complete_request(9)
• blk_mq_start_request(9)
• blk_execute_rq_nowait(9)
• blk_execute_rq(9)
• blk_mq_delay_run_hw_queue(9)
• blk_mq_run_hw_queue(9)
• blk_mq_run_hw_queues(9)
• blk_mq_delay_run_hw_queues(9)
• blk_mq_request_bypass_insert(9)
• blk_mq_try_issue_directly(9)
• blk_insert_cloned_request(9)
• blk_rq_unprep_clone(9)
• blk_rq_prep_clone(9)
• blk_mq_destroy_queue(9)

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and that's the page, bestie 🎀 go forth and submit those bios ✨

Sign-off time, fr fr: this one lives in ./block, and the date on it is October 2026. Slay. 💜