scribble_alloc(9)

💖 scribble_alloc(9) — a Kernel API Manual moment 💖

okay so bestie, this one's from the kernel API manual (section 9, the fancy "kernel internals" section, iykyk) and it's called scribble_alloc. yes, scribble. like the scratch paper of the kernel. we love an underrated icon 🎀

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✨ NAME ✨

scribble_alloc — allocate percpu scribble buffer for required size of the scribble region

like, it goes and gets you the scratch space. for one cpu's worth. that's the whole vibe 💅

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🦋 SYNOPSIS 🦋

int scribble_alloc (struct raid5_percpu *percpu , int num , int cnt );

returns an int, takes three args. no cap, that's it 🫶

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🌸 ARGUMENTS 🌸

• percpu — from for_each_present_cpu of the caller. so whoever's calling this is looping over the present cpus and hands you the one they're on rn 💜
• num — total number of disks in the array. the whole squad, not just the data ones ⭐
• cnt — scribble objs count for required size of the scribble region. literally the count of scribble objects that decides how big the region needs to be 🍓

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🔥 DESCRIPTION 🔥

okay so the whole point: the scribble buffer size must be enough to contain two things, and the manpage numbers them, so we're numbering them:

1. a struct page pointer for each device in the array +2
2. room to convert each entry in (1) to its corresponding dma (dma_map_page) or page (page_address) address

that's the requirement. that's the assignment. main character energy honestly 🌈

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👑 NOTE 👑

and before you ask about the +2 — the +2 is for the destination buffers of the ddf/raid6 case where we calculate over all devices (not just the data blocks), using zeros in place of the P and Q blocks. so it's not a random +2, it's a very deliberate +2, respect it 🙈

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💀 SEE ALSO 💀

Kernel file ./drivers/md/raid5.c

like, go read the actual source if you want the lore. it's all in there, fr fr 🧚

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so that's the page, bestie 💖 this little gem lives in ./drivers/md and it's dated October 2026, and yeah, the whole thing is signed scribble_alloc(9) — go forth and allocate your scribbles responsibly, mwah 💅✨