VOP_VPTOCNP(9)

💅 VOP_VPTOCNP(9) — the kernel dev manual page, but make it make sense

okay so bestie, this is a page from the Kernel Developer's Manual and it's literally called VOP_VPTOCNP, which lowkey looks like someone fell asleep on their keyboard but it's actually iconic — it's the vnode operation that turns a vnode back into its component name. yes, we're going backwards. main character energy fr fr 🦋

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✨ NAME ✨

VOP_VPTOCNP — translate a vnode to its component name. that's the whole vibe. one job. slay. 💅

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✨ SYNOPSIS ✨

like all good kernel things, you start with the includes:

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

and then the function itself:

int
VOP_VPTOCNP(struct vnode *vp, struct vnode **dvp, struct ucred *cred,
    char *buf, int *buflen);

yes bestie, that's five arguments. we don't do minimalism here. 🎀

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✨ DESCRIPTION ✨

so what does this actually do? it translates a vnode into its component name, and writes that name to the head of the buffer specified by buf. not the end, not the middle — the head. the way that it prepends is honestly so satisfying 😭✨

here's the cast of characters:

• vp — the vnode we're translating. the one getting the name reveal 🫶
• dvp — the vnode of the parent directory of vp. it's giving "who's your parent" energy.
• cred — the caller credentials. iykyk, permissions matter.
• buf — the buffer into which to prepend the component name. head of the buffer, remember!
• buflen — the remaining size of the buffer. not the total size, the remaining size. important. don't come for me.

and here's the tea about the default implementation 👀 it scans through vp's parent directory looking for a dirent with a matching file number. lowkey detective work. 🔍 but if vp is not a directory, then VOP_VPTOCNP returns ENOENT. so like, that's a no from her.

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✨ LOCKS ✨

lock lore, bestie, this part matters so don't skip it:

• the vnode should be locked on entry and will still be locked on exit. consistent queen 💜
• the parent directory vnode will be unlocked on a successful exit.
• but — and this is the plot twist — it will have its use count incremented. 🙈

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✨ RETURN VALUES ✨

zero on success. otherwise? an error code. that's it, that's the whole story. 🌈

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✨ ERRORS ✨

• [ENOMEM] — the buffer was not large enough to hold the vnode's component name. tragic. the buffer simply could not 💀
• [ENOENT] — the vnode was not found on the file system. she's missing. gone. not in this directory ✨

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✨ SEE ALSO ✨

go read these next, bestie, they're the supporting cast:

• vnode(9)
• VOP_LOOKUP(9)

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✨ NOTES ✨

this interface is a work in progress. 🚧 no cap. it's still cooking. be nice to it.

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✨ HISTORY ✨

the function VOP_VPTOCNP appeared in FreeBSD 8.0. throwback era, honestly. 🎀

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✨ AUTHORS ✨

this manual page was written by Joe Marcus Clarke. king behavior. 👑 we thank him for his service.

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mwah 💖 that's the whole page. this one came to you from the fine folks at Debian, dated March 8, 2015 — a vintage classic, fr fr. now go translate some vnodes, bestie, and remember: lock on entry, locked on exit, parent unlocked and use count incremented. periodt. 💅✨