writeback_iter(9)

📦 version 7.3.1, in nixpkgs unstable

💖 writeback_iter(9) 💖

okay so this is a page from the Kernel API Manual and it's all about writeback_iter — the little function that hands you folios one at a time while you're doing writeback. bestie, it's literally the backbone of your ->writepages implementation and i need you to respect it. 🫶

✨ NAME ✨

writeback_iter — iterate folio of a mapping for writeback

🌸 SYNOPSIS 🌸

struct folio * writeback_iter (struct address_space *mapping , struct
       writeback_control *wbc , struct folio *folio , int *error );

🎀 ARGUMENTS 🎀

  • mapping — the address space structure you wanna write, bestie. that's the whole target of the operation 💅
  • wbc — the writeback context. it's giving "here's how we're doing this writeback" energy
  • folio — the folio you iterated before. pass NULL to start, and then keep feeding back what you got 🦋
  • error — an in-out pointer for writeback errors (peep the description below, it matters 👀)

💜 DESCRIPTION 💜

so this function returns the next folio for the writeback operation described by wbc on mapping, and you should be calling it in a while loop inside your ->writepages implementation. no cap. that's the whole deal.

to start the writeback operation, you pass NULL in the folio argument — that's your opening move. then, for every subsequent iteration, you pass the folio you got back last time right back in. yes, it's a little handoff ritual, and honestly? iconic. ✨

if there was an error in the per-folio writeback inside the writeback_iter loop, error should be set to that error value. don't be shy about it, tell the truth to the pointer. 🙈

once the writeback described in wbc has finished, this function returns NULL — that's your "we're done here" moment — and if there was an error in any iteration, it restores it to error. so the error you stashed does not get lost, periodt.

🔥 NOTE 🔥

callers should not manually break out of the loop using break or goto — no ma'am, absolutely not. you must keep calling writeback_iter until it returns NULL. it's a whole commitment, like finishing a series. 💀

⭐ RETURN ⭐

the folio to write, or NULL if the loop is done. that's it, that's the answer. 👑

🌈 SEE ALSO 🌈

kernel file ./mm/page-writeback.c and all its friends:

and that's the whole page, bestie!! 💖 this one comes to you straight from ./mm (the source, mwah) and it's dated October 2026 — so like, very on-trend. go forth and iterate your folios responsibly 🧚‍♀️💅

📦 where this page comes from