devfs: Add devfs_{get,put}_device()

devfs_get_device() returns the device for a given path (if any), also
acquiring a reference to its vnode (thus ensuring the device won't go
away). devfs_put_device() puts the device vnode's reference.

src/system/kernel/device_manager/devfs.cpp

@@ -2143,6 +2143,34 @@ devfs_unpublish_device(BaseDevice* device, bool disconnect)
 }
 
 
+/*!	Gets the device for a given devfs relative path.
+	If successful the call must be balanced with a call to devfs_put_device().
+*/
+status_t
+devfs_get_device(const char* path, BaseDevice*& _device)
+{
+	devfs_vnode* node;
+	status_t status = get_node_for_path(sDeviceFileSystem, path, &node);
+	if (status != B_OK)
+		return status;
+
+	if (!S_ISCHR(node->stream.type) || node->stream.u.dev.partition != NULL) {
+		put_vnode(sDeviceFileSystem->volume, node->id);
+		return B_BAD_VALUE;
+	}
+
+	_device = node->stream.u.dev.device;
+	return B_OK;
+}
+
+
+void
+devfs_put_device(BaseDevice* device)
+{
+	put_vnode(sDeviceFileSystem->volume, device->ID());
+}
+
+
 void
 devfs_compute_geometry_size(device_geometry* geometry, uint64 blockCount,
 	uint32 blockSize)
@@ -2175,5 +2203,3 @@ devfs_publish_device(const char* path, device_hooks* hooks)
 {
 	return legacy_driver_publish(path, hooks);
 }
-
-

src/system/kernel/device_manager/devfs_private.h

@@ -16,8 +16,10 @@ namespace BPrivate {
 using BPrivate::BaseDevice;
 
 
-status_t devfs_publish_device(const char* path, BaseDevice* device);
-status_t devfs_unpublish_device(BaseDevice* device, bool disconnect);
-status_t devfs_get_device(dev_t device, ino_t node, BaseDevice** _device);
+status_t	devfs_publish_device(const char* path, BaseDevice* device);
+status_t	devfs_unpublish_device(BaseDevice* device, bool disconnect);
+
+status_t	devfs_get_device(const char* path, BaseDevice*& _device);
+void		devfs_put_device(BaseDevice* device);
 
 #endif	/* DEVFS_PRIVATE_H */