space_valid(9)

💅 space_valid(9) 💅

okay so real talk, bestie — this one lives in the Kernel API Manual and it's called space_valid, and honestly the name is doing exactly what it says on the tin. it validates free dpa space against constraints. no cap. 🦋

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✨ SYNOPSIS ✨

void space_valid (struct nd_region *nd_region , struct nvdimm_drvdata
*ndd , struct nd_label_id *label_id , struct resource *prev , struct
resource *next , struct resource *exist , resource_size_t n , struct
resource *valid );

like… that's a lot of arguments, i know, but we're gonna go through every single one together, hand in hand 🫶

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🎀 ARGUMENTS 🎀

• nd_region — the hosting region of the free space. it's giving "where the party's at" energy.
• ndd — dimm device data, but make it for debug. literally just there so you can peek at it when things go sideways 💀
• label_id — the namespace id that's about to get space allocated to it. main character of the allocation moment 👑
• prev — the potential allocation that comes right before the free space. front neighbor vibes.
• next — the allocation that follows the given free space range. back neighbor vibes.
• exist — the first allocation with the same id in the mapping. the og, the one that got there first ✨
• n — the range that must be satisfied for pmem allocations. lowkey important for the pmem girlies.
• valid — the free space range that we're actually validating. the whole point, honestly 🎯

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🌸 DESCRIPTION 🌸

okay so here's the tea ☕

BLK-space is valid as long as it does not precede a PMEM allocation in a given region. that's the rule, that's the whole rule, no exceptions, periodt.

PMEM-space has to be contiguous and adjacent to an existing allocation — but only if one exists, bestie, don't come for me. if there's no existing allocation to be adjacent to, then the adjacency requirement just isn't a thing, iykyk.

and if you're reserving PMEM? any space is valid 🔥 like, go off, choose your own adventure, the constraint is not constraining you.

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👀 SEE ALSO 👀

• Kernel file ./drivers/nvdimm/namespace_devs.c
• nd_is_uuid_unique(9)
• shrink_dpa_allocation(9)
• grow_dpa_allocation(9)
• namespace_update_uuid(9)
• create_namespace_pmem(9)

go read those next, they're all connected, it's a whole cinematic universe fr fr 🌈

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ngl this one is short but she's important — get the space validity wrong and your pmem allocation is not gonna have a good time 😭

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and that's the page! 🎀 from ./drivers/nvdimm, dated October 2026, this has been space_valid(9) — mwah, slay, bye bestie 💜🧚