VOP_ADVISE(9)

💅 VOP_ADVISE — apply advice about use of file data

okay so bestie, welcome to VOP_ADVISE(9) from the Kernel Developer's Manual — yes the kernel one, this is real main-character vnode energy and we're gonna get through it together 🫶

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✨ SYNOPSIS ✨

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

int
VOP_ADVISE(struct vnode *vp, off_t start, off_t end, int advice);

literally just one function, iconic, no notes 🔥

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🌸 DESCRIPTION 🌸

okay so this call applies advice for a range of a file's data — like you're dropping a little hint to the filesystem, no cap. fun fact: it's the thing that implements the posix_fadvise(2) system call. slay 🎀

here's its arguments, one by one:

• vp — the vnode of the file. the whole main character of this function ngl 💜
• start — the start of the range of file data.
• end — the end of the range of file data. and listen, a value of OFF_MAX means the advice applies all the way to the end of the file. iykyk 🌈
• advice — the type of operation to apply to the file data. possible values are:
  • POSIX_FADV_WILLNEED — initiate an asynchronous read of the file data if it's not already resident. like, "bestie i'm gonna need this, get it ready" ⭐
  • POSIX_FADV_DONTNEED — decrease the in-memory priority of clean file data, or just discard clean file data. yeah it said clean, read it again 🧚

also! if the start and end offsets are both zero, then the operation should be applied to the entire file 💖

🚨 okay this part matters: this call is advisory only. it may do the requested operation on a subset of the requested range — including not doing it at all — and still return success. so don't come for it, it warned you 😭 it's giving "i'll try my best" energy.

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🔒 LOCKS 🔒

the file should be unlocked on entry. unlock it before you call, bestie, fr fr 💅

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✅ RETURN VALUES ✅

0 is returned if the call is successful 🎉 otherwise an appropriate error code comes back at you. that's the whole vibe check.

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💀 ERRORS 💀

• [EINVAL] — an invalid value was given for advice. yeah. you gave it nonsense. it's not mad, it's just disappointed 🙈

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👑 SEE ALSO 👑

• vnode(9) — go read it, it's the whole family 🦋

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and that's the page, bestie!! go forth and advise responsibly ✨

— written under the Debian banner, dated September 26, 2015, from the Kernel Developer's Manual — periodt 💜