bitmap_from_u64(9)

💖 NAME 💖

okay so bestie, meet bitmap_from_u64 — it's a Kernel API Manual page (yes, bitmap_from_u64(9), that's her full name 💅) and her whole job is literally check and swap words within u64. that's it. that's the vibe. 🦋

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✨ SYNOPSIS ✨

void bitmap_from_u64 (unsigned long *dst , u64 mask );

like, she takes two things and returns nothing. void queen energy, no cap. 👑

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🎀 ARGUMENTS 🎀

• dst — the destination bitmap 🎯 (where the good stuff lands)
• mask — the source bitmap 🌸 (where the good stuff comes from)

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🦋 DESCRIPTION 🦋

okay so here's the tea ☕ and it's honestly such a specific little gremlin of a problem:

in a 32-bit Big Endian kernel, when you use (u32 *)(val)[*] to read a u64 mask, you get the wrong word. like, not me getting the wrong word 😭

that means (u32 *)(val)[0] grabs the upper 32 bits — but we expect the lower 32-bits of the u64. so, yeah, endianness said "not today bestie" and now this whole function exists to fix it. highkey iconic of her ngl. 🔥

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🌈 SEE ALSO 🌈

bestie, the whole friend group shows up here, so let's do a headcount 🫶:

• Kernel file ./include/linux/bitmap.h
• bitmap overview(9)
• bitmap bitops(9)
• declare bitmap(9)
• bitmap_find_next_zero_area(9)
• bitmap_or_equal(9)
• bitmap_weight_from(9)
• bitmap_scatter(9)
• bitmap_gather(9)
• bitmap_release_region(9)
• bitmap_allocate_region(9)
• bitmap_find_free_region(9)
• BITMAP_FROM_U64(9)
• bitmap_read(9)
• bitmap_write(9)

like literally the entire bitmap cinematic universe. go read them all, iykyk 💜

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fr fr, that's the whole page. she's short, she's specific, she's a little endian-coded icon. 🧚

and that's a wrap, bestie — this one came straight out of ./include/linux, dated October 2026, so you know it's fresh 🌸✨💖