Date: Sat, 18 Oct 2025 05:14:19 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: a4981ededef3 - main - kqueue.2: document KQUEUE_CPONFORK Message-ID: <202510180514.59I5EJCc062600@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=a4981ededef3c2d867ddd991905e4b65bc917a62 commit a4981ededef3c2d867ddd991905e4b65bc917a62 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2025-10-08 03:06:20 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2025-10-18 05:12:37 +0000 kqueue.2: document KQUEUE_CPONFORK Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 2 weeks Differential revision: https://reviews.freebsd.org/D52045 --- lib/libsys/kqueue.2 | 29 ++++++++++++++++++++++++++++- 1 file changed, 28 insertions(+), 1 deletion(-) diff --git a/lib/libsys/kqueue.2 b/lib/libsys/kqueue.2 index 96c9b0222a37..a8ebabf02cf7 100644 --- a/lib/libsys/kqueue.2 +++ b/lib/libsys/kqueue.2 @@ -97,10 +97,37 @@ system call also creates a new kernel event queue, and additionally takes a .Fa flags argument, which is a bitwise-inclusive OR of the following flags: -.Bl -tag -width "KQUEUE_CLOEXEC" +.Bl -tag -width "KQUEUE_CPONFORK" .It Dv KQUEUE_CLOEXEC The returned file descriptor is automatically closed on .Xr execve 2 +.It Dv KQUEUE_CPONFORK +When this flag is set, the created kqueue is copied into +the child process on +.Xr fork 2 +calls. +The kqueue descriptor index of the new kqueue will be inherited by the child, +that is, the numeric value of the descriptor will remain the same. +.Pp +Copying is deep, that is, each registered event in the original kqueue is +copied (and not shared) into the new kqueue. +This is contrary to how other descriptor types are handled upon +.Xr fork 2 , +where the copied file descriptor references the same file object +as the source descriptor (shallow copy). +.Pp +By default, in other words, when the flag is not set, kqueues from +the parent are not copied on fork to the child process. +The corresponding file descriptor indeces are unused in the child. +.Pp +Registered events that reference file descriptors which are not +duplicated on fork, are not copied into the new kqueue. +For instance, if the event references a file descriptor opened with the +.Dv O_CLOEXEC +flag set, it is not copied. +Similarly, if event references a kqueue opened without the +.Dv KQUEUE_CPONFORK +flag, the event is not copied. .El .Pp Thehome | help
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