VOP_OPEN(9)

💅 VOP_OPEN(9) — kernel dev manual energy ✨

okay so bestie, we're in the VOP_OPEN(9) page today — yes it's a kernel developer's manual page, yes it's about vnodes, and yes you're gonna slay it 🫶

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🌸 NAME 🌸

VOP_OPEN, VOP_CLOSE — open or close a file, literally that's the whole vibe 💖

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✨ SYNOPSIS ✨

#include <sys/param.h>
#include <sys/vnode.h>

int
VOP_OPEN(struct vnode *vp, int mode, struct ucred *cred,
    struct thread *td, struct file *fp);

int
VOP_CLOSE(struct vnode *vp, int mode, struct ucred *cred,
    struct thread *td);

look at those signatures, so clean, so iconic 👑

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🦋 DESCRIPTION 🦋

so here's the tea ☕ — the VOP_OPEN() entry point gets called before a file is accessed by a process, and VOP_CLOSE() gets called after a file is finished with by the process. that's it, that's the whole lifecycle arc, main character energy from start to finish 🎬

now the arguments, because of course we're doing the arguments:

• vp — the vnode of the file. that's your girl 🎀
• mode — the access mode required by the calling process.
• cred — the caller's credentials. yes, we're checking ids, no cap 🪪
• td — the thread which is accessing the file.
• fp — the file being opened.

a pointer to the file fp is genuinely useful for file systems which require such information, e.g., fdescfs(5). for in-kernel opens, just use NULL as the fp argument to VOP_OPEN() — lowkey handy 🙈

the access mode is a set of flags, including FREAD, FWRITE, O_NONBLOCK, O_APPEND. flags on flags on flags, we love to see it 🚩

and the thread td passed to VOP_CLOSE() may be NULL if the last reference to the open file is released from a kernel context — like, for example, the destruction of a socket buffer containing the file reference in a SCM_RIGHTS message. so NULL td is not a bug, it's just the kernel doing kernel things 💀

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🔒 LOCKS 🔒

okay this part matters, pay attention bestie 👀

VOP_OPEN() expects vp to be locked on entry, and will leave it locked on return. no funny business, it stays locked the whole time fr fr 🔐

VOP_CLOSE() expects at least a reference to be associated with the vnode, and genuinely does not care whether the vnode is locked or not. the lock and reference state is left unchanged on return. but — and this is the important part — note that vn_close expects an unlocked, referenced vnode and will dereference the vnode prior to returning. so don't hand it a locked one, that's not the assignment 😭

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⭐ RETURN VALUES ⭐

zero is returned on success. otherwise, an error code is returned. simple, clean, no notes 💫

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👑 SEE ALSO 👑

• vnode(9)
• VOP_LOOKUP(9)

go read those next, iykyk 📚

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🎀 AUTHORS 🎀

this manual page was written by Doug Rabson. legend behavior, honestly 🫡

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and that's the whole page, bestie — go forth and open and close files responsibly 💅✨

this lil sign-off comes to you from the Debian crew, dated October 17, 2025 — periodt 🎀