The branch main has been updated by dumbbell: URL: https://cgit.FreeBSD.org/src/commit/?id=5931649751847cc3ca54255bb767424dcb8a3e97
commit 5931649751847cc3ca54255bb767424dcb8a3e97 Author: Jean-Sébastien Pédron <[email protected]> AuthorDate: 2025-05-26 17:18:24 +0000 Commit: Jean-Sébastien Pédron <[email protected]> CommitDate: 2026-01-25 16:04:40 +0000 eventfd: Add refcounting An eventfd file descriptor can be used by drivers such as DRM drivers through linuxkpi. A driver can hold a reference to such a file regardless of the fact it is used by userland or not. This patch introduces a refcount in `struct eventfd`, plus the `eventfd_get()` and `eventfd_put()` functions to acquire and release references. These functions will be used by DRM drivers for instance. This structure is internal to `sys/kern/sys_eventfd.c` and not used anywhere else. Thus it is safe to add a field without breaking anything. Reviewed by: markj Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D50849 --- sys/kern/sys_eventfd.c | 30 ++++++++++++++++++++++++++++-- sys/sys/eventfd.h | 4 ++++ 2 files changed, 32 insertions(+), 2 deletions(-) diff --git a/sys/kern/sys_eventfd.c b/sys/kern/sys_eventfd.c index 04ed107c933d..433bcb57b2b3 100644 --- a/sys/kern/sys_eventfd.c +++ b/sys/kern/sys_eventfd.c @@ -40,6 +40,7 @@ #include <sys/mutex.h> #include <sys/poll.h> #include <sys/proc.h> +#include <sys/refcount.h> #include <sys/selinfo.h> #include <sys/stat.h> #include <sys/uio.h> @@ -102,6 +103,7 @@ struct eventfd { uint32_t efd_flags; struct selinfo efd_sel; struct mtx efd_lock; + unsigned int efd_refcount; }; int @@ -119,6 +121,7 @@ eventfd_create_file(struct thread *td, struct file *fp, uint32_t initval, efd->efd_count = initval; mtx_init(&efd->efd_lock, "eventfd", NULL, MTX_DEF); knlist_init_mtx(&efd->efd_sel.si_note, &efd->efd_lock); + refcount_init(&efd->efd_refcount, 1); fflags = FREAD | FWRITE; if ((flags & EFD_NONBLOCK) != 0) @@ -128,16 +131,39 @@ eventfd_create_file(struct thread *td, struct file *fp, uint32_t initval, return (0); } -static int -eventfd_close(struct file *fp, struct thread *td) +struct eventfd * +eventfd_get(struct file *fp) { struct eventfd *efd; + if (fp->f_data == NULL || fp->f_ops != &eventfdops) + return (NULL); + efd = fp->f_data; + refcount_acquire(&efd->efd_refcount); + + return (efd); +} + +void +eventfd_put(struct eventfd *efd) +{ + if (!refcount_release(&efd->efd_refcount)) + return; + seldrain(&efd->efd_sel); knlist_destroy(&efd->efd_sel.si_note); mtx_destroy(&efd->efd_lock); free(efd, M_EVENTFD); +} + +static int +eventfd_close(struct file *fp, struct thread *td) +{ + struct eventfd *efd; + + efd = fp->f_data; + eventfd_put(efd); return (0); } diff --git a/sys/sys/eventfd.h b/sys/sys/eventfd.h index 0f64483753e5..1f36dbecb92d 100644 --- a/sys/sys/eventfd.h +++ b/sys/sys/eventfd.h @@ -38,8 +38,12 @@ typedef uint64_t eventfd_t; #ifdef _KERNEL +struct eventfd; + int eventfd_create_file(struct thread *td, struct file *fp, uint32_t initval, int flags); +struct eventfd *eventfd_get(struct file *fp); +void eventfd_put(struct eventfd *efd); #else
