futex_atomi...chg_inatomic(9)

📦 version 7.3.1, in nixpkgs unstable

💅 futex_atomi...chg_inatomic — Kernel API Manual

okay so bestie, welcome to the Kernel API Manual ✨ this one's a very niche little number from the UML (user-mode-linux) side of things, and honestly? it's giving "atomic operations but make it architecture-specific" 🦋

🌸 NAME 🌸

futex_atomic_cmpxchg_inatomic — literally does a compare-and-exchange on the content of uaddr with newval, but only if the current value happens to be oldval 👑

like, no cap, that's the whole vibe. compare first, swap second, atomic the entire time 🎀

⭐ SYNOPSIS ⭐

int futex_atomic_cmpxchg_inatomic (u32 *uval , u32 __user *uaddr , u32 oldval , u32 newval );

yes the spacing is exactly like that, don't come for me, I'm just the messenger 🙈

🦋 ARGUMENTS 🦋

  • uval — pointer to store content of uaddr 💖 this is where the tea gets spilled afterwards, iykyk
  • uaddr — pointer to user space address 🌈 the main character location, fr fr
  • oldval — old value 👑 the value we're checking against, the "if it's still this, then…"
  • newval — new value to store to uaddr ✨ the glow-up we're applying if the vibe check passes

🔥 RETURN 🔥

  • 0 — On success 🎉 slay, it worked
  • -EFAULT — User access resulted in a page fault 💀 oop, the user memory said "not today"
  • -EAGAIN — Atomic operation was unable to complete due to contention 😭 it got crowded in there, try again bestie

💜 SEE ALSO 💜

🫶 ok but real talk: this is an atomic operation, so don't be out here assuming your normal lazy read-modify-write energy applies. The return codes are literally the whole story — 0 good, -EFAULT page fault, -EAGAIN contention. That's it, that's the plot 🍓

mwah 💋 that's the page! brought to you by the folks over at ./arch/um/kernel/skas, dated October 2026, and yeah — that's genuinely the whole thing. no notes. periodt 💅✨

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