follow_page_mask(9)

📦 version 7.3.1, in nixpkgs unstable

✨ follow_page_mask(9) ✨

okay so bestie, this one's from the Kernel API Manual and it's literally the glow-up page for looking up page descriptors 💅 like, given a user-virtual address, it finds the struct page for you. no cap.

🌸 SYNOPSIS 🌸

struct page * follow_page_mask (struct vm_area_struct *vma , unsigned
long address , unsigned int flags , unsigned long *page_mask );

like yes, that's the whole signature, no shortcuts 🎀

🦋 ARGUMENTS 🦋

  • vma — the vm_area_struct mapping address, aka where this whole thing lives 🗺️
  • address — the virtual address you're looking up, the main character of the operation ⭐
  • flags — the flags that modify how the lookup behaves, lowkey the personality settings 🔧
  • page_mask — a pointer to the output page_mask, it's giving "I'll tell you when we're done" 📤

💖 DESCRIPTION 💖

so flags can have FOLL_ flags set, and those are defined in <linux/mm.h> 💫 iykyk.

when you're getting an anonymous page and the caller has to trigger unsharing of a shared anonymous page first, -EMLINK is returned 😭 the caller should trigger a fault with FAULT_FLAG_UNSHARE set. and ngl, note that unsharing is only relevant with FOLL_PIN and !FOLL_WRITE — that's the vibe check right there 🫶

on output, page_mask is set according to the size of the page ✨

👑 RETURN 👑

it returns the mapped struct page *, or NULL if no mapping exists, or an error pointer if there's a mapping to something not represented by a page descriptor (see also vm_normal_page) 💀 like it's literally doing the most to be helpful.

🌈 SEE ALSO 🌈

all the Kernel file ./mm/gup.c besties, in the order the page lists them, periodt:

🫶 and that's the whole page, bestie — everything's here, nothing dropped, no details left on read.

okay and finally the sign-off: this lil beauty comes from ./mm, dated October 2026, and that's the tea 🍓✨ slay, go read gup.c now 💜

📦 where this page comes from