eventfd: Add eventfd_signal()
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Authored by dumbbell on Jun 14 2025, 5:23 PM.

Details

Reviewers

markj

Group Reviewers

linuxkpi

Summary

The eventfd_signal() function is the equivalent to a write to an eventfd file descriptor: it bumps the internal counter and wakes up processes waiting for it.

eventfd_signal() is meant to be used by kernel drivers. DRM drivers will call it through linuxkpi.

This is a requirement to the following patch to drm-kmod:
https://github.com/freebsd/drm-kmod/pull/358

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Repository

rG FreeBSD src repository

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Event Timeline

dumbbell created this revision.Jun 14 2025, 5:23 PM

Herald added subscribers: olce, imp. · View Herald TranscriptJun 14 2025, 5:23 PM

dumbbell requested review of this revision.Jun 14 2025, 5:23 PM

dumbbell edited the summary of this revision. (Show Details)Jun 14 2025, 5:50 PM

emaste added a parent revision: D50848: eventfd: Rename `struct eventfd` to `struct eventfd_ctx`.Jun 24 2025, 1:33 PM

emaste added a child revision: D50853: linuxkpi: Add eventfd_*().

markj accepted this revision.Sun, Nov 30, 4:42 PM

markj added a subscriber: markj.

markj added inline comments.

sys/kern/sys_eventfd.c
161	What's the purpose of having the `mask` parameter? Do you plan to extend this in the future?
170	It would be better to share this code with eventfd_write(), but it is not critical.

This revision is now accepted and ready to land.Sun, Nov 30, 4:42 PM

Refresh patch after abandonning D50848.

This revision now requires review to proceed.Sat, Dec 13, 9:41 PM

dumbbell mentioned this in D50848: eventfd: Rename `struct eventfd` to `struct eventfd_ctx`.Sat, Dec 13, 9:45 PM

dumbbell edited parent revisions, added: D50849: eventfd: Add refcounting; removed: D50848: eventfd: Rename `struct eventfd` to `struct eventfd_ctx`.

dumbbell removed a parent revision: D50849: eventfd: Add refcounting.Sat, Dec 13, 9:49 PM

christos added a subscriber: christos.Thu, Dec 18, 3:23 PM

christos added inline comments.

sys/kern/sys_eventfd.c
161	Same question as Mark. D50853 does not use it.

emaste added a subscriber: emaste.Thu, Dec 18, 3:52 PM

emaste added inline comments.

sys/kern/sys_eventfd.c
161	It matches Linux's `eventfd_signal_mask` but it does seem we could just omit it if not being used in FreeBSD.

markj added inline comments.Thu, Dec 18, 4:38 PM

sys/kern/sys_eventfd.c
161	This isn't the linuxkpi, so we shouldn't be duplicating the interface when it doesn't match our implementation.

emaste added inline comments.Thu, Dec 18, 4:58 PM

sys/kern/sys_eventfd.c
161	Arguably it should just be `eventfd_signal` as well?

dumbbell marked 6 inline comments as done.Thu, Dec 18, 6:44 PM

dumbbell added inline comments.

sys/kern/sys_eventfd.c
161	I will rename it to `eventfd_signal()` and get rid of `eventfd_signal_mask()` (which DRM doesn't use for now).
170	I will move this code to a dedicated function.

dumbbell marked 2 inline comments as done.Thu, Dec 18, 7:14 PM

dumbbell added inline comments.Thu, Dec 18, 7:16 PM

sys/kern/sys_eventfd.c
161	I will also change from using casts to `#define eventfd_ctx eventfd` because Linux code expects `eventfd_signal()` to take a `struct eventfd_ctx *` (the wrapper around `eventfd_signal_mask()` held the cast previously).