diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -751,8 +751,8 @@
 }
 
 #if OFF_MAX <= LONG_MAX
-off_t
-foffset_lock(struct file *fp, int flags)
+static int
+foffset_lock1(struct file *fp, int flags, off_t *offp)
 {
 	volatile short *flagsp;
 	off_t res;
@@ -760,16 +760,22 @@
 
 	KASSERT((flags & FOF_OFFSET) == 0, ("FOF_OFFSET passed"));
 
-	if ((flags & FOF_NOLOCK) != 0)
-		return (atomic_load_long(&fp->f_offset));
+	if ((flags & FOF_NOLOCK) != 0) {
+		*offp = atomic_load_long(&fp->f_offset);
+		return (0);
+	}
 
 	/*
 	 * According to McKusick the vn lock was protecting f_offset here.
 	 * It is now protected by the FOFFSET_LOCKED flag.
 	 */
 	flagsp = &fp->f_vnread_flags;
-	if (atomic_cmpset_acq_16(flagsp, 0, FOFFSET_LOCKED))
-		return (atomic_load_long(&fp->f_offset));
+	if (atomic_cmpset_acq_16(flagsp, 0, FOFFSET_LOCKED)) {
+		*offp = atomic_load_long(&fp->f_offset);
+		return (0);
+	}
+	if ((flags & FOF_NONBLOCK) != 0)
+		return (EAGAIN);
 
 	sleepq_lock(&fp->f_vnread_flags);
 	state = atomic_load_16(flagsp);
@@ -794,7 +800,8 @@
 	}
 	res = atomic_load_long(&fp->f_offset);
 	sleepq_release(&fp->f_vnread_flags);
-	return (res);
+	*offp = res;
+	return (0);
 }
 
 void
@@ -836,8 +843,8 @@
 	return (atomic_load_long(&fp->f_offset));
 }
 #else
-off_t
-foffset_lock(struct file *fp, int flags)
+int
+foffset_lock1(struct file *fp, int flags, off_t *offp)
 {
 	struct mtx *mtxp;
 	off_t res;
@@ -848,6 +855,10 @@
 	mtx_lock(mtxp);
 	if ((flags & FOF_NOLOCK) == 0) {
 		while (fp->f_vnread_flags & FOFFSET_LOCKED) {
+			if ((flags & FOF_NONBLOCK) != 0) {
+				mtx_unlock(mtxp);
+				return (EAGAIN);
+			}
 			fp->f_vnread_flags |= FOFFSET_LOCK_WAITING;
 			msleep(&fp->f_vnread_flags, mtxp, PUSER -1,
 			    "vofflock", 0);
@@ -856,7 +867,8 @@
 	}
 	res = fp->f_offset;
 	mtx_unlock(mtxp);
-	return (res);
+	*offp = res;
+	return (0);
 }
 
 void
@@ -892,6 +904,20 @@
 }
 #endif
 
+off_t
+foffset_lock(struct file *fp, int flags)
+{
+	off_t ret;
+	int error __diagused;
+
+	KASSERT((flags & FOF_NONBLOCK) == 0,
+	    ("FOF_NONBLOCK passed to foffset_lock()"));
+
+	error = foffset_lock1(fp, flags, &ret);
+	KASSERT(error == 0, ("foffset_lock1() failed: %d", error));
+	return (ret);
+}
+
 void
 foffset_lock_uio(struct file *fp, struct uio *uio, int flags)
 {
@@ -900,6 +926,13 @@
 		uio->uio_offset = foffset_lock(fp, flags);
 }
 
+int
+foffset_trylock(struct file *fp, int flags, off_t *offp)
+{
+
+	return (foffset_lock1(fp, flags | FOF_NONBLOCK, offp));
+}
+
 void
 foffset_unlock_uio(struct file *fp, struct uio *uio, int flags)
 {
diff --git a/sys/sys/file.h b/sys/sys/file.h
--- a/sys/sys/file.h
+++ b/sys/sys/file.h
@@ -85,7 +85,9 @@
 #define	FOF_NEXTOFF_R	0x04	/* Also update f_nextoff[UIO_READ] */
 #define	FOF_NEXTOFF_W	0x08	/* Also update f_nextoff[UIO_WRITE] */
 #define	FOF_NOUPDATE	0x10	/* Do not update f_offset */
+#define	FOF_NONBLOCK	0x20	/* Do not block if the offset is locked */
 off_t foffset_lock(struct file *fp, int flags);
+int foffset_trylock(struct file *fp, int flags, off_t *offp);
 void foffset_lock_uio(struct file *fp, struct uio *uio, int flags);
 void foffset_unlock(struct file *fp, off_t val, int flags);
 void foffset_unlock_uio(struct file *fp, struct uio *uio, int flags);