From 2c94b9eeb85c6cfa5ff918aa58ce484b27fc7c91 Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@apollo.backplane.com>
Date: Sun, 4 Jan 2015 20:54:56 -0800
Subject: [PATCH] devfs - Allow clone code to reuse an existing device

* Allow the clone code to set a replacement device which already exists
  in devfs.

* This will allow the sound code to cache virtual channel devices after
  use.
---
 sys/vfs/devfs/devfs_core.c  | 29 +++++++++++++++++++++++------
 sys/vfs/devfs/devfs_vnops.c | 18 +++++++++++-------
 2 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/sys/vfs/devfs/devfs_core.c b/sys/vfs/devfs/devfs_core.c
index 1767864b63..76b1ad1ec1 100644
--- a/sys/vfs/devfs/devfs_core.c
+++ b/sys/vfs/devfs/devfs_core.c
@@ -1430,7 +1430,7 @@ devfs_create_all_dev_worker(struct devfs_node *root)
 	KKASSERT(root);
 
 	TAILQ_FOREACH(dev, &devfs_dev_list, link) {
-		devfs_create_device_node(root, dev, NULL, NULL);
+		devfs_create_device_node(root, dev, NULL, NULL, NULL);
 	}
 
 	return 0;
@@ -1965,7 +1965,7 @@ devfs_resolve_name_path(char *fullpath, char *buf, char **pathp, char **namep)
  */
 struct devfs_node *
 devfs_create_device_node(struct devfs_node *root, cdev_t dev,
-			 char *dev_name, char *path_fmt, ...)
+			 int *existsp, char *dev_name, char *path_fmt, ...)
 {
 	struct devfs_node *parent, *node = NULL;
 	char *path = NULL;
@@ -1978,6 +1978,9 @@ devfs_create_device_node(struct devfs_node *root, cdev_t dev,
 
 	name_buf = kmalloc(PATH_MAX, M_TEMP, M_WAITOK);
 
+	if (existsp)
+		*existsp = 0;
+
 	if (path_fmt != NULL) {
 		__va_start(ap, path_fmt);
 		kvasnrprintf(&path, PATH_MAX, 10, path_fmt, ap);
@@ -1995,9 +1998,23 @@ devfs_create_device_node(struct devfs_node *root, cdev_t dev,
 		parent = devfs_resolve_or_create_path(parent, create_path, 1);
 
 
-	if (devfs_find_device_node_by_name(parent, name)) {
-		devfs_debug(DEVFS_DEBUG_WARNING, "devfs_create_device_node: "
-			"DEVICE %s ALREADY EXISTS!!! Ignoring creation request.\n", name);
+	node = devfs_find_device_node_by_name(parent, name);
+	if (node) {
+		if (node->d_dev == dev) {
+			/*
+			 * Allow case where device caches dev after the
+			 * close and might desire to reuse it.
+			 */
+			if (existsp)
+				*existsp = 1;
+		} else {
+			devfs_debug(DEVFS_DEBUG_WARNING,
+				    "devfs_create_device_node: "
+				    "DEVICE %s ALREADY EXISTS!!! "
+				    "Ignoring creation request.\n",
+				    name);
+			node = NULL;
+		}
 		goto out;
 	}
 
@@ -2175,7 +2192,7 @@ devfs_propagate_dev(cdev_t dev, int attach)
 		if (attach) {
 			/* Device is being attached */
 			devfs_create_device_node(mnt->root_node, dev,
-						 NULL, NULL );
+						 NULL, NULL, NULL);
 		} else {
 			/* Device is being detached */
 			devfs_alias_remove(dev);
diff --git a/sys/vfs/devfs/devfs_vnops.c b/sys/vfs/devfs/devfs_vnops.c
index 2430be7b17..d0894dd214 100644
--- a/sys/vfs/devfs/devfs_vnops.c
+++ b/sys/vfs/devfs/devfs_vnops.c
@@ -865,6 +865,8 @@ devfs_spec_open(struct vop_open_args *ap)
 	vn_lock(vp, LK_UPGRADE | LK_RETRY);
 
 	if (node && ap->a_fp) {
+		int exists;
+
 		devfs_debug(DEVFS_DEBUG_DEBUG, "devfs_spec_open: -1.1-\n");
 		lockmgr(&devfs_lock, LK_EXCLUSIVE);
 
@@ -874,12 +876,13 @@ devfs_spec_open(struct vop_open_args *ap)
 		if (ndev != NULL) {
 			newnode = devfs_create_device_node(
 					DEVFS_MNTDATA(vp->v_mount)->root_node,
-					ndev, NULL, NULL);
+					ndev, &exists, NULL, NULL);
 			/* XXX: possibly destroy device if this happens */
 
 			if (newnode != NULL) {
 				dev = ndev;
-				devfs_link_dev(dev);
+				if (exists == 0)
+					devfs_link_dev(dev);
 
 				devfs_debug(DEVFS_DEBUG_DEBUG,
 						"parent here is: %s, node is: |%s|\n",
@@ -891,7 +894,8 @@ devfs_spec_open(struct vop_open_args *ap)
 						((struct devfs_node *)(TAILQ_LAST(DEVFS_DENODE_HEAD(node->parent), devfs_node_head)))->d_dir.d_name);
 
 				/*
-				 * orig_vp is set to the original vp if we cloned.
+				 * orig_vp is set to the original vp if we
+				 * cloned.
 				 */
 				/* node->flags |= DEVFS_CLONED; */
 				devfs_allocv(&vp, newnode);
@@ -901,10 +905,10 @@ devfs_spec_open(struct vop_open_args *ap)
 		}
 		lockmgr(&devfs_lock, LK_RELEASE);
 		/*
-		 * Synchronize devfs here to make sure that, if the cloned device
-		 * creates other device nodes in addition to the cloned one,
-		 * all of them are created by the time we return from opening
-		 * the cloned one.
+		 * Synchronize devfs here to make sure that, if the cloned
+		 * device creates other device nodes in addition to the
+		 * cloned one, all of them are created by the time we return
+		 * from opening the cloned one.
 		 */
 		if (ndev)
 			devfs_config();
-- 
2.41.0