cdevpriv(9): add iterator

Reviewed by:	christos
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D44469

sys/fs/devfs/devfs_vnops.c

@@ -177,6 +177,26 @@ devfs_set_cdevpriv(void *priv, d_priv_dtor_t *priv_dtr)
 	return (error);
 }
 
+int
+devfs_foreach_cdevpriv(struct cdev *dev, int (*cb)(void *data, void *arg),
+    void *arg)
+{
+	struct cdev_priv *cdp;
+	struct cdev_privdata *p;
+	int error;
+
+	cdp = cdev2priv(dev);
+	error = 0;
+	mtx_lock(&cdevpriv_mtx);
+	LIST_FOREACH(p, &cdp->cdp_fdpriv, cdpd_list) {
+		error = cb(p->cdpd_data, arg);
+		if (error != 0)
+			break;
+	}
+	mtx_unlock(&cdevpriv_mtx);
+	return (error);
+}
+
 void
 devfs_destroy_cdevpriv(struct cdev_privdata *p)
 {

sys/sys/conf.h

@@ -319,6 +319,8 @@ typedef void d_priv_dtor_t(void *data);
 int	devfs_get_cdevpriv(void **datap);
 int	devfs_set_cdevpriv(void *priv, d_priv_dtor_t *dtr);
 void	devfs_clear_cdevpriv(void);
+int	devfs_foreach_cdevpriv(struct cdev *dev,
+	    int (*cb)(void *data, void *arg), void *arg);
 
 ino_t	devfs_alloc_cdp_inode(void);
 void	devfs_free_cdp_inode(ino_t ino);