UNION IDLE_PBN_LOCK(9)

💅 union idle_pbn_lock(9)

okay bestie, welcome to the Kernel API Manual — yes, that manual — and today's main character is the page union idle_pbn_lock(9). it's giving very niche, very kernel-internals, and honestly? kinda iconic. let's get into it 🫶

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✨ NAME ✨

union idle_pbn_lock — the PBN lock list entries, bestie. that's the whole vibe check.

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🌸 SYNOPSIS 🌸

here's the glow-up, exactly as it is, no cap:

union idle_pbn_lock {
    struct list_head entry;
    struct pbn_lock lock;
 };

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🎀 Members 🎀

• entry — literally only used while the locks are hanging out in the pool. pool era. 🏊
• lock — and this one? only used while the locks are not in the pool. out-of-pool era. main character energy, off on its own. ✨

it's a union, so these two share the same memory — only one of them is doing anything at any given time. iykyk 💅

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🦋 Description 🦋

so the unused (idle) PBN locks are kept in a list. and here's the cute part: just like in a malloc implementation, the lock structure is basically unused memory while it's sitting there doing nothing. so we can save a bit of space — and also not pollute the lock structure proper — by using a union to overlay the lock structure with the free list. 🧚

like, why waste bytes when you can just vibe-share them? literally efficient. it's giving "reuse, reduce, recycle" but for kernel memory. 🌈

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👑 SEE ALSO 👑

okay the friend group is massive, here we go — all of these live in the Kernel file ./drivers/md/dm-vdo/physical-zone.c:

• vdo_is_pbn_read_lock(9)
• vdo_downgrade_pbn_write_lock(9)
• vdo_claim_pbn_lock_increment(9)
• vdo_assign_pbn_lock_provisional_reference(9)
• vdo_unassign_pbn_lock_provisional_reference(9)
• release_pbn_lock_provisional_reference(9)
• struct pbn_lock_pool(9)
• return_pbn_lock_to_pool(9)
• make_pbn_lock_pool(9)
• free_pbn_lock_pool(9)
• borrow_pbn_lock_from_pool(9)
• initialize_zone(9)
• vdo_make_physical_zones(9)
• vdo_free_physical_zones(9)
• vdo_get_physical_zone_pbn_lock(9)
• vdo_attempt_physical_zone_pbn_lock(9)
• allocate_and_lock_block(9)
• retry_allocation(9)
• continue_allocating(9)
• vdo_allocate_block_in_zone(9)
• vdo_release_physical_zone_pbn_lock(9)
• vdo_dump_physical_zone(9)

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bestie fr fr, read those before you touch the union. the whole pool ecosystem is right there. 🔥

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and that's the page! source/version is ./drivers/md/dm-vdo, dated October 2026 — so mark your calendar, screenshot it, frame it, whatever. slay, bye! 💖🎀💜