Add new make_dev_p(9) flag MAKEDEV_ETERNAL to inform devfs that created

cdev will never be destroyed. Propagate the flag to devfs vnodes as
VV_ETERNVALDEV. Use the flags to avoid acquiring devmtx and taking a
thread reference on such nodes.

In collaboration with:	pho
MFC after:	1 month

1 files changed, 15 insertions, 7 deletions

diff --git a/sys/sys/conf.h b/sys/sys/conf.h
index 82ea088..6c60601 100644
--- a/sys/sys/conf.h
+++ b/sys/sys/conf.h
@@ -54,6 +54,7 @@ struct file;
 struct cdev {
 	void		*__si_reserved;
 	u_int		si_flags;
+#define	SI_ETERNAL	0x0001	/* never destroyed */
 #define SI_ALIAS	0x0002	/* carrier of alias name */
 #define SI_NAMED	0x0004	/* make_dev{_alias} has been called */
 #define SI_CHEAPCLONE	0x0008	/* can be removed_dev'ed when vnode reclaims */
@@ -249,9 +250,9 @@ int	destroy_dev_sched(struct cdev *dev);
 int	destroy_dev_sched_cb(struct cdev *dev, void (*cb)(void *), void *arg);
 void	destroy_dev_drain(struct cdevsw *csw);
 void	drain_dev_clone_events(void);
-struct cdevsw *dev_refthread(struct cdev *_dev);
-struct cdevsw *devvn_refthread(struct vnode *vp, struct cdev **devp);
-void	dev_relthread(struct cdev *_dev);
+struct cdevsw *dev_refthread(struct cdev *_dev, int *_ref);
+struct cdevsw *devvn_refthread(struct vnode *vp, struct cdev **devp, int *_ref);
+void	dev_relthread(struct cdev *_dev, int _ref);
 void	dev_depends(struct cdev *_pdev, struct cdev *_cdev);
 void	dev_ref(struct cdev *dev);
 void	dev_refl(struct cdev *dev);
@@ -262,10 +263,11 @@ struct cdev *make_dev(struct cdevsw *_devsw, int _unit, uid_t _uid, gid_t _gid,
 struct cdev *make_dev_cred(struct cdevsw *_devsw, int _unit,
 		struct ucred *_cr, uid_t _uid, gid_t _gid, int _perms,
 		const char *_fmt, ...) __printflike(7, 8);
-#define	MAKEDEV_REF     0x1
-#define	MAKEDEV_WHTOUT	0x2
-#define	MAKEDEV_NOWAIT	0x4
-#define	MAKEDEV_WAITOK	0x8
+#define	MAKEDEV_REF     0x01
+#define	MAKEDEV_WHTOUT	0x02
+#define	MAKEDEV_NOWAIT	0x04
+#define	MAKEDEV_WAITOK	0x08
+#define	MAKEDEV_ETERNAL	0x10
 struct cdev *make_dev_credf(int _flags,
 		struct cdevsw *_devsw, int _unit,
 		struct ucred *_cr, uid_t _uid, gid_t _gid, int _mode,
@@ -279,6 +281,12 @@ void	dev_lock(void);
 void	dev_unlock(void);
 void	setconf(void);
 
+#ifdef KLD_MODULE
+#define	MAKEDEV_ETERNAL_KLD	0
+#else
+#define	MAKEDEV_ETERNAL_KLD	MAKEDEV_ETERNAL
+#endif
+
 #define	dev2unit(d)	((d)->si_drv0)
 
 typedef	void (*cdevpriv_dtr_t)(void *data);