get_futex_key(9)

💖 get_futex_key(9) 💖

okay bestie, welcome to the Kernel API Manual page for get_futex_key(9) — this one is literally about getting the parameters that are the keys for a futex. no cap, it’s a little kernel-key situation and we’re keeping every detail. 🫶✨

🌸 NAME 🌸

get_futex_key — Get parameters which are the keys for a futex

✨ SYNOPSIS ✨

int get_futex_key (u32 __user *uaddr , unsigned int flags , union
futex_key *key , enum futex_access rw );

🎀 ARGUMENTS 🎀

• uaddr — virtual address of the futex
• flags — FLAGS_*
• key — address where result is stored.
• rw — mapping needs to be read/write (values: FUTEX_READ, FUTEX_WRITE)

🔥 RETURN 🔥

a negative error code or 0

🦋 DESCRIPTION 🦋

The key words are stored in key on success.

For shared mappings (when fshared), the key is:

( inode->i_sequence, page offset within mapping, offset_within_page )

[ also see get_inode_sequence_number ]

For private mappings (or when !fshared), the key is:

( current->mm, address, 0 )

This allows (cross process, where applicable) identification of the futex without keeping the page pinned for the duration of the FUTEX_WAIT.

⚠️ lock_page might sleep, the caller should not hold a spinlock. 💀

🔗 SEE ALSO 🔗

Kernel file ./kernel/futex/core.c — also peep these:

• __futex_hash(9)
• futex_setup_timer(9)
• fault_in_user_writeable(9)
• futex_top_waiter(9)
• wait_for_owner_exiting(9)
• __futex_unqueue(9)
• futex_unqueue(9)
• futex_exit_recursive(9)

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okay that’s the whole page, bestie! source/version ./kernel/futex, date October 2026, and the page is get_futex_key(9). mwah 💅💖✨