vmemdup_user(9)

📦 version 7.3.1, in nixpkgs unstable

✨ vmemdup_user — the kernel API manual, but make it make sense ✨

okay so bestie, this is a page from the Kernel API Manual (section 9, the kernel-API girlies) and we're talking about vmemdup_user — literally one of the most useful little functions in the whole mm friend group 💖

🌸 NAME 🌸

vmemdup_user — duplicate a memory region that lives in user space 🫶

like, you've got a blob of memory over in userspace and you want your very own kernel-side copy? that's her. that's the whole job.

🎀 SYNOPSIS 🎀

void * vmemdup_user (const void __user *src , size_t len );

so you hand her a src and a len and she hands you back a void *. iconique. no cap.

🦋 ARGUMENTS 🦋

  • src — the source address, and bestie it is in user space. mind the __user annotation, she's not kidding around 💅
  • len — number of bytes to copy. that's it. that's the size. how many bytes. 🍓

🌈 RETURN 🌈

lowkey the important part, so pay attention:

  • on failure you get back an ERR_PTR — so fr fr check it, don't just start dereferencing 😭
  • heads up: the result may be not physically contiguous 🫠 so don't go assuming anything about physical layout
  • and when you're done with it, free it with kvfree. periodt. not kfree, not vfree, kvfree. 👑

💜 SEE ALSO 💜

this list is long but we do not skip, we do not summarise, we respect the whole squad. the kernel file is ./mm/util.c and here's everybody:

bestie reminder: ERR_PTR check first, kvfree to clean up, and don't assume it's physically contiguous. that's the whole vibe check 💀

and that's the page!! sourced from the ./mm directory, dated October 2026, and filed under vmemdup_user(9) — mwah, go write some good kernel code, i'm obsessed with you already 💅✨🎀

📦 where this page comes from