futex_atomic...inuser_local(9)

✨ futex_atomic_op_inuser_local(9) ✨

okay so bestie, we're in the Kernel API Manual today and this one is a whole function for doing atomic math on a futex value and then checking whether it matched 💅 like — atomic arithmetic op with a constant argument, PLUS a comparison of the previous futex value against another constant. two jobs, one function, main character energy fr fr 🎀

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🌸 NAME 🌸

futex_atomic_op_inuser_local — Atomic arithmetic operation with constant argument and comparison of the previous futex value with another constant.

yes bestie that NAME line is the entire plot 😭 read it twice, it's dense but it ate.

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🦋 SYNOPSIS 🦋

int futex_atomic_op_inuser_local (int op , u32 oparg , int *oval , u32
__user *uaddr );

four params, one int coming back at you, no cap ✨

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💖 ARGUMENTS 💖

• op — the operation to execute 👑 this is the what are we even doing of it all
• oparg — argument of the operation 🍓 the constant you're feeding in
• oval — previous value at uaddr on successful return 🌸 so if it slays, the old value gets parked here
• uaddr — pointer to user space address 🦋 yeah it's a u32 __user *, it's pointing into userspace, be normal about it

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🔥 RETURN 🔥

• 0 — on success 💖 we love a zero, flawless victory, periodt
• -EFAULT — user access resulted in a page fault 😭 the address was not it
• -EAGAIN — atomic operation was unable to complete due to contention 💀 somebody else was in the way, try again
• -ENOSYS — operation not supported 🙈 this op is simply not invited to the party

ngl bestie, always check your return value. 0 is the only one that's giving happy ending 🌈

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⭐ SEE ALSO ⭐

• Kernel file ./include/asm-generic/futex.h — go read the source, it's right there 🫶
• futex_atomic_cmpxchg_inatomic_local(9) — the sibling function, same energy, different vibe 💜

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okay that's the whole page, you ate that 🎀 this lil beauty lives under ./include/asm-generic, dated October 2026, and it's filed as futex_atomic...inuser_local(9) in the Kernel API Manual — mwah, go forth and futex responsibly bestie 💅✨🧚