bitmap_read(9)

💖 bitmap_read(9) — the kernel API manual, but make it cute 💖

okay so bestie, welcome to bitmap_read(9), a page from the big official Kernel API Manual and honestly? it's a little icon. tiny function, huge main character energy. it reads a value of n-bits out of a memory region and hands it to you like a lil gift 🎀

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✨ NAME ✨

bitmap_read — read a value of n-bits from the memory region. that's it, that's the whole vibe. no cap. 💅

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🌸 SYNOPSIS 🌸

unsigned long bitmap_read (const unsigned long *map , unsigned long
start , unsigned long nbits );

look at her. one line-ish of pure C, returning an unsigned long. she slays, she reads bits, she leaves. 🔥

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🦋 ARGUMENTS 🦋

• map — the address to the bitmap memory region, aka where the bits actually live. this is the destination of your little field trip 🗺️
• start — the bit offset of the n-bit value. so like, where you're starting from, bestie. not byte offset, bit offset, iykyk 👀
• nbits — the size of the value in bits. must be nonzero, and it goes up to BITS_PER_LONG — that's the ceiling, don't push it 🙈

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👑 RETURN 👑

you get back the value of nbits bits that live at the start bit offset inside the map memory region. literally exactly what you asked for, no notes 💖

okay but the important part, and I need you to actually read this one: for nbits = 0 and for nbits > BITS_PER_LONG, the return value is undefined. undefined, bestie. not zero, not a fun surprise — undefined. do not pass go, do not collect your bits 💀

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🌈 SEE ALSO 🌈

the whole extended friend group, fr fr:

• 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_from_u64(9)
• bitmap_write(9) — yes, the other one. the writer. her sibling 💜

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that's the whole page, you ate that 🫶 this cutie lives over in ./include/linux, dated October 2026, and she's filed under bitmap_read(9) — go forth and read some bits, queen 👑✨