From 7236f2c2204245cee636e681cfccc666472cc6ed Mon Sep 17 00:00:00 2001
From: Dmitry Chagin <dchagin@FreeBSD.org>
Date: Sun, 24 May 2015 16:36:29 +0000
Subject: [PATCH] For future use in the Linuxulator:

1. Add a kern_kqueue() counterpart for kqueue() with flags parameter.

2. Be a bit secure. To avoid a double fp lookup add a kern_kevent_fp()
counterpart for kern_kevent() with file pointer parameter instead
of file descriptor an pass the buck to it.

Suggested by: mjg [2]

Differential Revision:	https://reviews.freebsd.org/D1091
Reviewed by:	trasz
---
 sys/kern/kern_event.c | 35 ++++++++++++++++++++++++++---------
 sys/sys/syscallsubr.h |  4 ++++
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index b6d8a7973022..9000addbc29b 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -736,6 +736,13 @@ filt_usertouch(struct knote *kn, struct kevent *kev, u_long type)
 
 int
 sys_kqueue(struct thread *td, struct kqueue_args *uap)
+{
+
+	return (kern_kqueue(td, 0));
+}
+
+int
+kern_kqueue(struct thread *td, int flags)
 {
 	struct filedesc *fdp;
 	struct kqueue *kq;
@@ -757,7 +764,7 @@ sys_kqueue(struct thread *td, struct kqueue_args *uap)
 	PROC_UNLOCK(p);
 
 	fdp = p->p_fd;
-	error = falloc(td, &fp, &fd, 0);
+	error = falloc(td, &fp, &fd, flags);
 	if (error)
 		goto done2;
 
@@ -888,12 +895,9 @@ int
 kern_kevent(struct thread *td, int fd, int nchanges, int nevents,
     struct kevent_copyops *k_ops, const struct timespec *timeout)
 {
-	struct kevent keva[KQ_NEVENTS];
-	struct kevent *kevp, *changes;
-	struct kqueue *kq;
-	struct file *fp;
 	cap_rights_t rights;
-	int i, n, nerrors, error;
+	struct file *fp;
+	int error;
 
 	cap_rights_init(&rights);
 	if (nchanges > 0)
@@ -904,9 +908,24 @@ kern_kevent(struct thread *td, int fd, int nchanges, int nevents,
 	if (error != 0)
 		return (error);
 
+	error = kern_kevent_fp(td, fp, nchanges, nevents, k_ops, timeout);
+	fdrop(fp, td);
+
+	return (error);
+}
+
+int
+kern_kevent_fp(struct thread *td, struct file *fp, int nchanges, int nevents,
+    struct kevent_copyops *k_ops, const struct timespec *timeout)
+{
+	struct kevent keva[KQ_NEVENTS];
+	struct kevent *kevp, *changes;
+	struct kqueue *kq;
+	int i, n, nerrors, error;
+
 	error = kqueue_acquire(fp, &kq);
 	if (error != 0)
-		goto done_norel;
+		return (error);
 
 	nerrors = 0;
 
@@ -946,8 +965,6 @@ kern_kevent(struct thread *td, int fd, int nchanges, int nevents,
 	error = kqueue_scan(kq, nevents, k_ops, timeout, keva, td);
 done:
 	kqueue_release(kq, 0);
-done_norel:
-	fdrop(fp, td);
 	return (error);
 }
 
diff --git a/sys/sys/syscallsubr.h b/sys/sys/syscallsubr.h
index a6dca3139308..4ff111ee8a3e 100644
--- a/sys/sys/syscallsubr.h
+++ b/sys/sys/syscallsubr.h
@@ -121,6 +121,10 @@ int	kern_jail_get(struct thread *td, struct uio *options, int flags);
 int	kern_jail_set(struct thread *td, struct uio *options, int flags);
 int	kern_kevent(struct thread *td, int fd, int nchanges, int nevents,
 	    struct kevent_copyops *k_ops, const struct timespec *timeout);
+int	kern_kevent_fp(struct thread *td, struct file *fp, int nchanges,
+	    int nevents, struct kevent_copyops *k_ops,
+	    const struct timespec *timeout);
+int	kern_kqueue(struct thread *td, int flags);
 int	kern_kldload(struct thread *td, const char *file, int *fileid);
 int	kern_kldstat(struct thread *td, int fileid, struct kld_file_stat *stat);
 int	kern_kldunload(struct thread *td, int fileid, int flags);