blk_mq_unique_tag(9)

✨ blk_mq_unique_tag(9) ✨

okay so bestie, welcome to the Kernel API Manual 💅 this one's a lil function called blk_mq_unique_tag and honestly? it's giving "tiny function, big responsibility." let's get into it 🫶

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🌸 NAME 🌸

blk_mq_unique_tag — return a tag that is unique queue-wide 🎀

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🦋 SYNOPSIS 🦋

u32 blk_mq_unique_tag (struct request *rq );

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⭐ ARGUMENTS ⭐

• rq — the request you want a unique tag computed for, like "here's my request, pls give me a tag bestie" 🙈

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💖 DESCRIPTION 💖

Okay so here's the vibe check 👑 the tag field inside struct request is unique per hardware queue, but not across all hardware queues — which is lowkey a problem if you need a tag that's actually unique everywhere, y'know? 😭

So this function exists fr fr: it returns a tag where the hardware context index lives in the upper bits and the per hardware queue tag sits in the lower bits. Upper bits + lower bits = one iconic, queue-wide unique tag periodt 💅✨

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🎀 NOTE 🎀

Heads up bestie 🫶 when you call this for a request that's queued on a non-multiqueue request queue, the hardware context index gets set to zero. No cap, that's just how it is 💀

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🌈 SEE ALSO 🌈

Kernel file ./block/blk-mq-tag.c plus all these besties:

• bt_for_each(9)
• 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)

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and that's the whole page, you ate that 🍓💜 this lil gem lives under ./block in the source, dated October 2026, and it's part of the blk_mq_unique_tag(9) manual — go forth and tag things uniquely, queen 👑💅