bt_for_each(9)

💖 bt_for_each — like, the kernel manual page for it ✨

bestie, this is bt_for_each from the Kernel API Manual, and it is literally about iterating over the requests associated with a hardware queue 🌸 it's giving "walk the tags, one rq at a time" energy and honestly? iconic.

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✨ NAME ✨

bt_for_each — iterate over the requests associated with a hardware queue 🎀

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🦋 SYNOPSIS 🦋

void bt_for_each (struct blk_mq_hw_ctx *hctx , struct request_queue *q ,
struct sbitmap_queue *bt , busy_tag_iter_fn *fn , void *data , bool
reserved );

okay so it takes six things and returns void, no cap 💅

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👑 ARGUMENTS 👑

• hctx — the hardware queue you want to examine. that's the one, bestie 🔍
• q — the request queue that hctx is associated with, aka hctx->queue. yep, that exact member 🫶
• bt — the sbitmap to examine. this is either the breserved_tags member or the bitmap_tags member of struct blk_mq_tags — pick your fighter, but only those two 🌈
• fn — a pointer to the function that gets called for each request associated with hctx that has been assigned a driver tag. it's called like this:

fn(rq, data)

where rq is a pointer to a request. return true to keep iterating tags; return false to stop 🔥 like, that's the whole vibe check right there — false means you're done, periodt.

• data — gets passed as the second argument to fn. it's your little payload, carrying whatever you need 🎀
• reserved — tells you whether bt is the breserved_tags member or the bitmap_tags member of struct blk_mq_tags ⭐ (yes it's the same either/or situation from bt, it's just being confirmed here, k?)

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🌸 SEE ALSO 🌸

• Kernel file ./block/blk-mq-tag.c bt_tags_for_each(9)
• blk_mq_all_tag_iter(9)
• blk_mq_tagset_busy_iter(9)
• blk_mq_tagset_wait_completed_request(9)
• blk_mq_queue_tag_busy_iter(9)
• blk_mq_unique_tag(9)

go read those too, they're all in the same friend group fr fr 💜

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mwah 💋 this page lives in ./block, the date on it is October 2026, and it's the bt_for_each(9) page from the Kernel API Manual — that's the whole sign-off bestie, go iterate some tags 🧚‍♀️✨