VRELE(9)

💅 VRELE(9) — the kernel dev manual, bestie edition 🎀

okay so this is the page for vput, vrele, and vunref — the three little gremlins that all do the same vibe: decrement the use count for a vnode. yes they're from the Kernel Developer's Manual, and yes they're lowkey iconic.

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✨ NAME ✨

vput, vrele, vunref — decrement the use count for a vnode

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🌸 SYNOPSIS 🌸

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

void
vput(struct vnode *vp);

void
vrele(struct vnode *vp);

void
vunref(struct vnode *vp);

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🦋 DESCRIPTION 🦋

So the whole entire job of these three is: decrement the v_usecount field of a vnode. that's it. that's the post. 💅

Here's the one argument you're gonna be passing around like it's the aux cord:

• vp — the vnode to decrement

Now let's meet the trio, because they are not the same girlies even though they look alike:

• vrele() — takes an unlocked vnode, and returns with the vnode unlocked. so it goes in chill and comes out chill. no cap.
• vput() — should be given a locked vnode as its argument, and the vnode is unlocked after the function returns. and here's the tea 👀 — vput() is operationally equivalent to calling VOP_UNLOCK(9) followed by vrele(), just with less overhead. so it's the same fit, but snatched and efficient.
• vunref() — takes a locked vnode as its argument, and returns with the vnode locked. goes in locked, comes out locked. consistency queen.

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Any code in the system which signified its use of a vnode by usecount should call one of the listed function to decrement use counter. like, that's the whole point. If the v_usecount field of the non-doomed vnode reaches zero, then it will be inactivated and placed on the free list. bye bestie, off to the free list you go 🫶

Heads up though — the vrele() function may lock the vnode. And all three functions may sleep. so don't be out here calling them in places where sleeping is illegal, that's not the vibe 😭

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The hold count for the vnode is always greater or equal to the usecount. fr fr, always. And non-forced unmount fails when a mount point owns a vnode that has a non-zero usecount — see vflush(9). so if your unmount is acting up, check your usecounts, that's the main character energy you're looking for 💀

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🔥 SEE ALSO 🔥

• vget(9)
• vnode(9)
• vref(9)
• vrefcnt(9)

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👑 AUTHORS 👑

This manual page was written by Doug Rabson and Konstantin Belousov. absolute legends, we stan 💖

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and that's the page!! go forth and decrement responsibly, bestie. this lil beauty came to you from Debian, dated February 24, 2016 — vintage but still slaying ✨🦋🌸