binder_do_fd_close(9)

📦 version 7.3.1, in nixpkgs unstable

💅 binder_do_fd_close(9) — from the Kernel API Manual ✨

okay so bestie, we're in the kernel API manual today and the star of the show is binder_do_fd_close, a function whose whole entire job is closing a list of file descriptors — but like, at the right time, not just whenever. timing is everything, iykyk 🎀

🌸 SYNOPSIS 🌸

void binder_do_fd_close (struct callback_head *twork );

🦋 ARGUMENTS 🦋

  • twork — the callback head for task work. it's giving "my whole identity is being a callback" and honestly? respect 💅

✨ DESCRIPTION ✨

okay so here's the tea, and it's actually important: it is not safe to call ksys_close during the binder_ioctl function if there's even a chance that binder's own file descriptor might get closed. like, that's the whole reason, and it exists to meet the requirements for using fdget (go read the comments for __fget_light if you want the full lore, bestie 📖).

so instead of doing the risky thing, we use task_work_add to schedule the close operation for after we've returned from binder_ioctl. slay, deferred execution, we love to see it 👑

this function right here? it's the callback for that whole mechanism — and it does the actual ksys_close on the given file descriptor. so it's like the main character who shows up at the very end to actually do the thing. no cap, that's the entire vibe 💖

💜 SEE ALSO 💜

kernel file ./drivers/android/binder.c — plus this absolutely iconic lineup of related pages:

genuine reminder bestie: the ksys_close-during-binder_ioctl thing isn't a suggestion, it's a not safe. don't do it. let task work handle it. 🫶

and that's the page!! this one lives under ./drivers/android, dated October 2026, and it's binder_do_fd_close(9) — go forth and close your fds responsibly, mwah 💋✨

📦 where this page comes from