sys_flock(9)

💖 sys_flock(9) 💖

okay so bestie, quick vibe check: this is one of those kernel API manual pages — it's sys_flock, which is literally the kernel-side implementation of the flock() system call. yes, that flock. the file-locking one. we love a syscall with main character energy 🐑

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✨ SYNOPSIS ✨

long sys_flock (unsigned int fd , unsigned int cmd );

that's the whole signature, that's the assignment. two unsigned ints in, one long out. slay 💅

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🎀 ARGUMENTS 🎀

• fd — the file descriptor you wanna lock. the thing being locked. your target, your muse, your file 💖
• cmd — the type of lock to apply. which flavour of locking we're doing today. keep reading, there's a whole menu 🍓

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🦋 DESCRIPTION 🦋

so what it does: it applies a FL_FLOCK style lock to an open file descriptor. that's the whole bit. that's the job ✨

and the cmd you pass can be one of these little icons:

• LOCK_SH — a shared lock 🌸 multiple friends can hold it at the same time, everyone's chilling
• LOCK_EX — an exclusive lock 🔥 one holder only, everyone else can go touch grass
• LOCK_UN — remove an existing lock. bye bestie, unlock, free the file 🫶
• LOCK_MAND — a 'mandatory' flock. (DEPRECATED) 💀

ok so real talk about LOCK_MAND: LOCK_MAND support has been removed from the kernel. it's gone-gone. not "use at your own risk" gone, removed. the kernel said no cap and meant it 😭 so don't come crying to me when it doesn't work, i warned you, i literally italicised it

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🌈 SEE ALSO 🌈

bestie i need you to brace yourself, this list is long. like, suspiciously long. it's giving "the locking subsystem is a whole friend group." anyway, here's everyone the page links arms with 💜

the kernel file to go stare at is ./fs/locks.c, and then:

• locks_owner_has_blockers(9)
• lease_open_conflict(9)
• locks_delete_block(9)
• posix_lock_file(9)
• posix_lock_inode_wait(9)
• inode_lease_ignore_mask(9)
• __break_lease(9)
• lease_get_mtime(9)
• __fcntl_getlease(9)
• generic_setlease(9)
• vfs_setlease(9)
• fcntl_setlease(9)
• fcntl_setdeleg(9)
• flock_lock_inode_wait(9)
• locks_lock_inode_wait(9)
• vfs_test_lock(9)
• locks_translate_pid(9)
• vfs_lock_file(9)
• vfs_cancel_lock(9)
• vfs_inode_has_locks(9)

twenty whole siblings. twenty. and every single one of them is invited to the group chat 👑

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okay that's the page!! mwah 💋 it came from ./fs, and it's dated October 2026 — so yeah, it's got a whole calendar moment going on. go forth and lock responsibly, bestie 🧚💖