test_and_set_bit(9)

💅 test_and_set_bit(9) — like, the Kernel API Manual page you actually wanna read

okay bestie, welcome to the Kernel API Manual, section 9, and today's main character is test_and_set_bit 💖

---

✨ NAME ✨

test_and_set_bit — set a bit and return its old value. that's it, that's the whole vibe 🎀

---

🌸 SYNOPSIS 🌸

bool test_and_set_bit (long nr , volatile unsigned long *addr );

literally just hand it a bit number and an address and it does the thing, no cap ✨

---

🦋 ARGUMENTS 🦋

• nr — the bit you wanna set. which one? that one. the *nr*th one 🎯
• addr — the address to count from. start counting here, bestie 🫶

---

🔥 DESCRIPTION 🔥

so this is an atomic fully-ordered operation — the docs literally say it comes with an implied full memory barrier. it's giving main character energy, it's giving "i don't need anyone to hold my hand" 😭👑

⚠️ okay but fr fr, "fully-ordered" is not a cute little detail, it's the whole point. don't go assuming you can reorder stuff around it.

---

👑 SEE ALSO 👑

• the kernel file itself: ./include/asm-generic/bitops/instrumented-atomic.h — go read it, iykyk 🍓
• set_bit(9)
• clear_bit(9)
• change_bit(9)
• test_and_clear_bit(9)
• test_and_change_bit(9)

the whole bit-twiddling friend group, honestly 🌈

---

and that's the page!! 💜 this one's from ./include/asm-generic/bitops, dated October 2026, and it's test_and_set_bit(9) forever and always — slay, go set some bits, mwah 🧚💅