evdev: add devnum sysctl

Add a sysctl entry for the evdev device number (devnum) to allow
libudev-devd to populate the corresponding device information
fields (MAJOR and MINOR) when running in a jail with no input devices
exposed through devfs.

Signed-off-by: Quentin Thébault <quentin.thebault@defenso.fr>

Reviewed by:	wulf
Sponsored by:	Defenso
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D56968

sys/dev/evdev/evdev.c

@@ -283,6 +283,11 @@ evdev_sysctl_create(struct evdev_dev *evdev)
 	    SYSCTL_CHILDREN(ev_sysctl_tree), OID_AUTO, "sw_bits", CTLFLAG_RD,
 	    evdev->ev_sw_flags, sizeof(evdev->ev_sw_flags), "",
 	    "Input device supported switch events");
+
+	SYSCTL_ADD_U64(&evdev->ev_sysctl_ctx,
+	    SYSCTL_CHILDREN(ev_sysctl_tree), OID_AUTO, "devnum", CTLFLAG_RD,
+	    &evdev->ev_devnum, 0,
+	    "Input device number");
 }
 
 static int
@@ -328,6 +333,7 @@ evdev_register_common(struct evdev_dev *evdev)
 	ret = evdev_cdev_create(evdev);
 	if (ret != 0)
 		goto bail_out;
+	evdev->ev_devnum = dev2udev(evdev->ev_cdev);
 
 	/* Create sysctls (for device enumeration without /dev/input access rights) */
 	evdev_sysctl_create(evdev);

sys/dev/evdev/evdev_private.h

@@ -114,6 +114,7 @@ struct evdev_dev
 	uid_t			ev_cdev_uid;
 	gid_t			ev_cdev_gid;
 	int			ev_cdev_mode;
+	dev_t			ev_devnum;
 	int			ev_unit;
 	enum evdev_lock_type	ev_lock_type;
 	struct mtx *		ev_state_lock;	/* State lock */