bdev_deny_freeze(9)

📦 version 7.3.1, in nixpkgs unstable

💅 bdev_deny_freeze(9) — the Kernel API Manual, bestie edition 🎀

okay so real talk, this is a page from the Kernel API Manual and the function's whole personality is bdev_deny_freeze — it's the vibe-check bouncer for block devices. let's get into it ✨

🌸 NAME 🌸

bdev_deny_freeze — makes a block device unfreezable, no cap 🧊🚫

✨ SYNOPSIS ✨

int bdev_deny_freeze (struct block_device *bdev );

like yes that's the whole signature, she's lowkey minimal 💅

🦋 ARGUMENTS 🦋

  • bdev — the block device. that's it. that's the whole argument. the main character of this function fr 🫶

👑 DESCRIPTION 👑

so here's the tea ☕ — bdev_deny_freeze reserves bdev against bdev_freeze, and it does it the exact same way deny_write_access reserves a file against writers. iconic lineage, honestly 👑

the secret sauce is bd_fsfreeze_count, which is sign-encoded (yes, sign-encoded, she contains multitudes):

  • > 0 counts the active freezes ❄️
  • < 0 counts the deniers 🙅‍♀️

so a deny only succeeds while no freeze is in progress. like, you cannot barge in mid-freeze, that's not the move. and while the deny is held, bdev_freeze returns -EBUSY — the door is locked from the inside 🚪🔒

💖 always pair this with bdev_allow_freeze — you cannot just leave it denied forever, that's not slay behaviour, that's a leak.

and why do we care?? because when a filesystem is removing, adding, or replacing a member device, it denies freezes on that device for the duration. the whole point is that a claim a freeze walk might act on is never torn down behind the freezer's back 🫣 — no sneaky surprises, no backstabbing, we don't do that here.

one thing to keep in your notes app 📝: the deny is device-scoped, not (device, superblock)-scoped. so if a device is shared by several superblocks, it gets refused for all of them. no sharing, no splitting, it's all-or-nothing energy 💀

and for the record — no in-tree filesystem removes a shared claim from a live superblock. that's just not a thing that happens. periodt. 🎀

🔥 RETURN 🔥

  • 0 — we're so back, the deny landed ✅
  • -EBUSY — the device is currently frozen, try again later bestie 😭

🌈 SEE ALSO 🌈

the lore continues in the kernel file ./block/bdev.c — go read it, iykyk 📖✨

and that's the page!! 🎀 from the ./block corner of the world, dated October 2026 — mwah, go freeze responsibly, ily, bye 💜🦋⭐

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