ceph_start_io_read(9)

📦 version 7.3.1, in nixpkgs unstable

💖 ceph_start_io_read — Kernel API Manual, bestie edition 💖

okay so we're in the Kernel API Manual today and the star of the show is ceph_start_io_read(9). she's a little function with a big job, and honestly? she ate. let's get into it 🫶

✨ NAME ✨

ceph_start_io_read — bestie, this literally just declares that the file is being used for buffered reads. that's the whole vibe. 💅

🌸 SYNOPSIS 🌸

int ceph_start_io_read (struct inode *inode );

no cap, that's it. one argument, one int coming back at you. iconic ✨

🎀 ARGUMENTS 🎀

  • inode — the file inode. that's her. that's the girl. 🦋

💜 DESCRIPTION 💜

so here's the situation. when you call this, you're announcing "hey, a buffered read operation is about to start" — and you're also making sure we block all direct I/O. like, all of it. no direct I/O sneaking in during your read, not on her watch. 🚫

on exit, the function makes sure the CEPH_I_ODIRECT flag is unset, and it holds a shared lock on inode->i_rwsem so that the flag literally cannot be changed while you're holding it. locked down. immovable. periodt. 🔒

in practice, what does that mean? it means buffered read operations are allowed to execute in parallel, thanks to that shared lock — the girls are all reading together, no queue, no drama, we love a shared-lock moment 🌈. meanwhile direct I/O operations need to wait to grab an exclusive lock in order to set CEPH_I_ODIRECT. so they're lowkey stuck in line while the reads are out here living their best life 😭💀.

also pls note: buffered writes and truncates both take a write lock on inode->i_rwsem, which means those are serialised with respect to the reads. so it's not chaos in there — writes and truncates are politely waiting their turn while the reads do their parallel thing. main character energy is shared, we stan fair scheduling 🧚💖

👑 SEE ALSO 👑

go read them all, they're the rest of the friend group and they're all slaying in their own way 🦋✨

aaand that's the page!! 🎀 this one's from ./fs/ceph, dated October 2026, and we're out here repping ceph_start_io_read(9) — stay buffered, stay shared-locked, and don't let direct I/O cut the line 💜💅🔥

📦 where this page comes from