backing_file_open(9)

💅 backing_file_open — like, the kernel's very own backstage pass

okay so bestie, welcome to backing_file_open(9) from the Kernel API Manual — this is the little function that lets the kernel open a backing file for its own internal use, and honestly? it's giving support-system realness. 🎀

✨ SYNOPSIS ✨

struct file * backing_file_open (const struct file *user_file , int
       flags , const struct path *real_path , const struct cred *cred );

🌸 ARGUMENTS 🌸

• user_file — the file the user actually asked to open. the main character, the one they think they're touching 🫶
• flags — the open flags, standard issue, nothing spicy
• real_path — the path of the backing file. the real one. the one behind the curtain 👀
• cred — credentials used for the open, because even kernel internals gotta show ID

🦋 DESCRIPTION 🦋

So here's the vibe: we're opening a backing file for a stackable filesystem — think overlayfs, that kind of situation. 💖

user_file->f_path might live on the stackable filesystem, while real_path lives on the underlying filesystem. Different layers, same energy.

And in that case? We want to be able to return the path of the stackable filesystem, not the underneath one. Slay. How do we do it? We embed the returned file into a container structure that also stores the stacked file's path — and you can pull that back out later using backing_file_user_path. no cap, that's the whole trick 🧚

🎀 SEE ALSO 🎀

Kernel file ./fs/backing-file.c — go read it, iykyk 📖✨

and that's the page, bestie! this one's from ./fs, dated October 2026 — periodt. 💜🌈