blk_lld_busy(9)

📦 version 7.3.1, in nixpkgs unstable

💅 blk_lld_busy — check if the low-key drivers under a device are busy

okay so this is a page from the Kernel API Manual (section 9, bestie — we're in kernel-space now 💖), and it's all about blk_lld_busy. yes the name is a mouthful. no we're not renaming it. let's go 🎀

✨ NAME ✨

blk_lld_busy — check if underlying low-level drivers of a device are busy

like, are the drivers underneath this thing swamped or not. that's the whole vibe check. 🦋

🌸 SYNOPSIS 🌸

int blk_lld_busy (struct request_queue *q );

one function, one pointer, one int coming back at ya. periodt.

🧚 ARGUMENTS 🧚

  • q — the queue of the device being checked

that's it. that's the whole argument list. the queue, the device, the thing we're snooping on. 👑

💜 DESCRIPTION 💜

Okay so real talk: this function checks if the underlying low-level drivers of a device are busy.

and here's the crucial part, bestie — if the drivers wanna export their busy state, they must set their own exporting function using blk_queue_lld_busy first. like, you don't just get to be busy and have nobody know about it. you have to actually sign up for the whole "i'm busy" announcement system. no signup, no signal. 🙈

Basically? This function is used only by request stacking drivers — and it's for stopping them from dispatching requests to underlying devices while those underlying devices are busy. the way that works out is honestly so good for everyone involved:

  • it helps more I/O merging on the queue of the request stacking driver 🔥
  • and it prevents I/O throughput regression on burst I/O load ⭐

so yeah, it's giving "hold up, let me not pile on" and honestly? iconic behaviour. the whole point is keeping the queue chill so things merge nicely instead of everything getting yeeted at a busy device and tanking your throughput. 👑

🔥 RETURN 🔥

  • 0 — Not busy (the request stacking driver should dispatch request) ✅ go ahead bestie, send it
  • 1 — Busy (the request stacking driver should stop dispatching request) 🛑 pump the brakes, we're full

binary decisions only, no nuance, no maybe, no "it's complicated". fr fr.

🫶 SEE ALSO 🫶

the kernel file ./block/blk-core.c is where the magic lives, and here's the whole squad of related functions — go read them, they're all main character energy in their own way 💖:

and that's the whole page, bestie 🌈 it came out of the ./block directory, dated October 2026, and it goes by blk_lld_busy(9) if you need to look it up again. mwah 💋✨

📦 where this page comes from