1 files changed, 588 insertions, 86 deletions

diff --git a/lib/sysfs_device.c b/lib/sysfs_device.c
index 185b5cf..83c3adc 100644
--- a/lib/sysfs_device.c
+++ b/lib/sysfs_device.c
@@ -3,7 +3,7 @@
  *
  * Generic device utility functions for libsysfs
  *
- * Copyright (C) 2003 International Business Machines, Inc.
+ * Copyright (C) IBM Corp. 2003
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
@@ -24,17 +24,185 @@
 #include "sysfs.h"
 
 /**
+ * get_dev_driver: fills in the dev->driver_name field, but searches by
+ *	opening subsystem. Only to be used if no driver link exists in
+ *	device directory.
+ *
+ * Returns 0 on SUCCESS and 1 on error
+ */
+static int get_dev_driver(struct sysfs_device *dev)
+{
+	struct dlist *drvlist = NULL;
+	char path[SYSFS_PATH_MAX], devpath[SYSFS_PATH_MAX];
+	char *drv = NULL, *c = NULL;
+	
+	if (dev == NULL) {
+		errno = EINVAL;
+		return 1;
+	}
+	if (dev->bus[0] == '\0')
+		return 1;
+	memset(path, 0, SYSFS_PATH_MAX);
+	memset(devpath, 0, SYSFS_PATH_MAX);
+	safestrcpy(path, SYSFS_BUS_NAME);
+	safestrcat(path, "/");
+	safestrcat(path, dev->bus);
+	safestrcat(path, "/");
+	safestrcat(path, SYSFS_DRIVERS_NAME);
+
+	safestrcpy(devpath, dev->path);
+	c = strstr(devpath, SYSFS_DEVICES_NAME);
+	if (c == NULL)
+		return 1;
+	*c = '\0';
+	safestrcatmax(c, path, (sizeof(devpath) - strlen(devpath)));
+
+	drvlist = sysfs_open_subsystem_list(path);
+	if (drvlist != NULL) {
+		dlist_for_each_data(drvlist, drv, char) {
+			safestrcpy(path, devpath);
+			safestrcat(path, "/");
+			safestrcat(path, drv);
+			safestrcat(path, "/");
+			safestrcat(path, dev->bus_id);
+			if (sysfs_path_is_link(path) == 0) {
+				safestrcpy(dev->driver_name, drv);
+				sysfs_close_list(drvlist);
+				return 0;
+			}
+		}
+		sysfs_close_list(drvlist);
+	}
+	return 1;
+}
+
+/*
+ * get_device_driver_name: gets device's driver name, searches for driver
+ *	link first before going the brute force route.
+ * @dev: device to retrieve driver
+ * returns 0 with success and 1 with error
+ */
+static int get_device_driver_name(struct sysfs_device *dev)
+{
+	char devpath[SYSFS_PATH_MAX], drvpath[SYSFS_PATH_MAX];
+
+	if (dev == NULL) {
+		errno = EINVAL;
+		return 1;
+	}
+	memset(devpath, 0, SYSFS_PATH_MAX);
+	memset(drvpath, 0, SYSFS_PATH_MAX);
+	safestrcpy(devpath, dev->path);
+	safestrcat(devpath, "/driver");
+
+	if ((sysfs_get_link(devpath, drvpath, SYSFS_PATH_MAX)) != 0) 
+		return(get_dev_driver(dev));
+
+	return (sysfs_get_name_from_path(drvpath, dev->driver_name, 
+		SYSFS_NAME_LEN));
+}
+	
+/**
+ * sysfs_get_device_bus: retrieves the bus name the device is on, checks path 
+ * 	to bus' link to make sure it has correct device.
+ * @dev: device to get busname.
+ * returns 0 with success and -1 with error.
+ */
+int sysfs_get_device_bus(struct sysfs_device *dev)
+{
+	char subsys[SYSFS_NAME_LEN], path[SYSFS_PATH_MAX];
+	char target[SYSFS_PATH_MAX], *bus = NULL, *c = NULL;
+	struct dlist *buslist = NULL;
+
+	if (dev == NULL) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	memset(subsys, 0, SYSFS_NAME_LEN);
+	safestrcpy(subsys, SYSFS_BUS_NAME);  /* subsys = bus */
+	buslist = sysfs_open_subsystem_list(subsys);
+	if (buslist != NULL) {
+		dlist_for_each_data(buslist, bus, char) {
+			memset(path, 0, SYSFS_PATH_MAX);
+			safestrcpy(path, dev->path);
+			c = strstr(path, "/devices");
+			if (c == NULL) {
+				dprintf("Invalid path to device %s\n", path);
+				sysfs_close_list(buslist);
+				return -1;
+			}
+			*c = '\0';
+			safestrcat(path, "/");
+			safestrcat(path, SYSFS_BUS_NAME);
+			safestrcat(path, "/");
+			safestrcat(path, bus);
+			safestrcat(path, "/");
+			safestrcat(path, SYSFS_DEVICES_NAME);
+			safestrcat(path, "/");
+			safestrcat(path, dev->bus_id);
+			if ((sysfs_path_is_link(path)) == 0) {
+				memset(target, 0, SYSFS_PATH_MAX);
+				if ((sysfs_get_link(path, target, 
+						SYSFS_PATH_MAX)) != 0) {
+					dprintf("Error getting link target\n");
+					sysfs_close_list(buslist);
+					return -1;
+				}
+				if (!(strncmp(target, dev->path, 
+							SYSFS_PATH_MAX))) {
+					safestrcpy(dev->bus, bus);
+					sysfs_close_list(buslist);
+					return 0;
+				}
+			}
+                }
+                sysfs_close_list(buslist);
+        }
+        return -1;
+}
+
+/**
+ * sysfs_close_device_tree: closes every device in the supplied tree, 
+ * 	closing children only.
+ * @devroot: device root of tree.
+ */
+void sysfs_close_device_tree(struct sysfs_device *devroot)
+{
+	if (devroot != NULL) {
+		if (devroot->children != NULL) {
+			struct sysfs_device *child = NULL;
+
+			dlist_for_each_data(devroot->children, child,
+					struct sysfs_device) {
+				sysfs_close_device_tree(child);
+			}
+		}
+		sysfs_close_device(devroot);
+	}
+}
+
+/**
+ * sysfs_close_dev_tree: routine for dlist integration
+ */
+static void sysfs_close_dev_tree(void *dev)
+{
+	sysfs_close_device_tree((struct sysfs_device *)dev);
+}
+
+/**
  * sysfs_close_device: closes and cleans up a device
  * @dev = device to clean up
  */
 void sysfs_close_device(struct sysfs_device *dev)
 {
 	if (dev != NULL) {
-		dev->next = NULL;
-		dev->driver = NULL;
+		if (dev->parent != NULL)
+			sysfs_close_device(dev->parent);
 		if (dev->directory != NULL)
 			sysfs_close_directory(dev->directory);
-		dev->children = NULL;
+		if (dev->children != NULL && dev->children->count == 0)
+			dlist_destroy(dev->children);
 		free(dev);
 	}
 }
@@ -49,151 +217,485 @@ static struct sysfs_device *alloc_device(void)
 }
 
 /**
- * sysfs_get_device_attr: searches dev's attributes by name
- * @dev: device to look through
- * @name: attribute name to get
- * returns sysfs_attribute reference with success or NULL with error.
+ * open_device_dir: opens up sysfs_directory for specific root dev
+ * @name: name of root
+ * returns struct sysfs_directory with success and NULL with error
  */
-struct sysfs_attribute *sysfs_get_device_attr(struct sysfs_device *dev,
-						const char *name)
+static struct sysfs_directory *open_device_dir(const char *path)
 {
-	struct sysfs_attribute *cur = NULL;
-	char attrname[SYSFS_NAME_LEN];
+	struct sysfs_directory *rdir = NULL;
 
-	if (dev == NULL || dev->directory == NULL || name == NULL) {
+	if (path == NULL) {
 		errno = EINVAL;
 		return NULL;
 	}
-	for (cur = dev->directory->attributes; cur != NULL; cur = cur->next) {
-		if ((sysfs_get_name_from_path(cur->path, attrname, 
-		    SYSFS_NAME_LEN)) != 0) 
-			continue;
-		if (strcmp(name, attrname) != 0)
-			continue;
 
-		return cur;
+	rdir = sysfs_open_directory(path);
+	if (rdir == NULL) {
+		errno = EINVAL;
+		dprintf ("Device %s not supported on this system\n", path);
+		return NULL;
 	}
-
-	return NULL;
+	if ((sysfs_read_dir_subdirs(rdir)) != 0) {
+		dprintf ("Error reading device at dir %s\n", path);
+		sysfs_close_directory(rdir);
+		return NULL;
+	}
+	
+	return rdir;
 }
 
 /**
- * sysfs_open_device: opens and populates device structure
+ * sysfs_open_device_path: opens and populates device structure
  * @path: path to device, this is the /sys/devices/ path
  * returns sysfs_device structure with success or NULL with error
  */
-struct sysfs_device *sysfs_open_device(const char *path)
+struct sysfs_device *sysfs_open_device_path(const char *path)
 {
 	struct sysfs_device *dev = NULL;
-	struct sysfs_directory *sdir = NULL;
-	char *p = NULL;
 
 	if (path == NULL) {
 		errno = EINVAL;
 		return NULL;
 	}
+	if ((sysfs_path_is_dir(path)) != 0) {
+		dprintf("Incorrect path to device: %s\n", path);
+		return NULL;
+	}
 	dev = alloc_device();	
 	if (dev == NULL) {
-		dprintf(stderr, "Error allocating device at %s\n", path);
+		dprintf("Error allocating device at %s\n", path);
 		return NULL;
 	}
-	sdir = sysfs_open_directory(path);
-	if (sdir == NULL) {
-		dprintf(stderr, "Invalid device at %s\n", path);
+	if ((sysfs_get_name_from_path(path, dev->bus_id, 
+					SYSFS_NAME_LEN)) != 0) {
 		errno = EINVAL;
+		dprintf("Error getting device bus_id\n");
 		sysfs_close_device(dev);
 		return NULL;
 	}
-	if ((sysfs_read_directory(sdir)) != 0) {
-		dprintf(stderr, "Error reading device directory at %s\n", path);
-		sysfs_close_directory(sdir);
+	safestrcpy(dev->path, path);
+	if ((sysfs_remove_trailing_slash(dev->path)) != 0) {
+		dprintf("Invalid path to device %s\n", dev->path);
 		sysfs_close_device(dev);
 		return NULL;
 	}
-	dev->directory = sdir;
-	sysfs_get_name_from_path(sdir->path, dev->bus_id, SYSFS_NAME_LEN);
-	/* get device name */
-	p = sysfs_get_value_from_attributes(sdir->attributes,	
-							SYSFS_NAME_ATTRIBUTE);
-	if (p != NULL) {
-		strncpy(dev->name, p, SYSFS_NAME_LEN);
-		p = dev->name + strlen(dev->name) - 1;
-		if ((strlen(dev->name) > 0) && *p == '\n')
-			*p = '\0';
+	/* 
+	 * The "name" attribute no longer exists... return the device's
+	 * sysfs representation instead, in the "dev->name" field, which
+	 * implies that the dev->name and dev->bus_id contain same data.
+	 */
+	safestrcpy(dev->name, dev->bus_id);
+	
+	if (sysfs_get_device_bus(dev) != 0)
+		dprintf("Could not get device bus\n");
+	
+	if (get_device_driver_name(dev) != 0) {
+		dprintf("Could not get device %s's driver\n", dev->bus_id);
+		safestrcpy(dev->driver_name, SYSFS_UNKNOWN);
 	}
 
 	return dev;
 }
 
 /**
- * sysfs_close_device_tree: closes every device in the supplied tree, 
- * 	closing children only.
- * @devroot: device root of tree.
+ * sysfs_open_device_tree: opens root device and all of its children,
+ *	creating a tree of devices. Only opens children.
+ * @path: sysfs path to devices
+ * returns struct sysfs_device and its children with success or NULL with
+ *	error.
  */
-void sysfs_close_device_tree(struct sysfs_device *devroot)
+struct sysfs_device *sysfs_open_device_tree(const char *path)
 {
-	if (devroot != NULL) {
-		if (devroot->children != NULL) {
-			struct sysfs_device *child = NULL, *next = NULL;
-	
-			for (child = devroot->children; child != NULL;
-			     child = next) {
-				next = child->next;
-				sysfs_close_device_tree(child);
+	struct sysfs_device *rootdev = NULL, *new = NULL;
+	struct sysfs_directory *cur = NULL;
+
+	if (path == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+	rootdev = sysfs_open_device_path(path);
+	if (rootdev == NULL) {
+		dprintf("Error opening root device at %s\n", path);
+		return NULL;
+	}
+	if (rootdev->directory == NULL) {
+		rootdev->directory = open_device_dir(rootdev->path);
+		if (rootdev->directory == NULL) 
+			return NULL;
+	}
+	if (rootdev->directory->subdirs != NULL) {
+		dlist_for_each_data(rootdev->directory->subdirs, cur,
+				struct sysfs_directory) {
+			new = sysfs_open_device_tree(cur->path);
+			if (new == NULL) {
+				dprintf("Error opening device tree at %s\n",
+					cur->path);
+				sysfs_close_device_tree(rootdev);
+				return NULL;
 			}
+			if (rootdev->children == NULL)
+				rootdev->children = dlist_new_with_delete
+					(sizeof(struct sysfs_device),
+					sysfs_close_dev_tree);
+			dlist_unshift_sorted(rootdev->children, 
+							new, sort_list);
 		}
-		sysfs_close_device(devroot);
 	}
+
+	return rootdev;
 }
 
 /**
- * add_device_child_to_parent: adds child device to parent
- * @parent: parent device.
- * @child: child device to add.
+ * sysfs_close_root_device: closes root and all devices
+ * @root: root device to close
  */
-static void add_device_child_to_parent(struct sysfs_device *parent,
-					struct sysfs_device *child)
+void sysfs_close_root_device(struct sysfs_root_device *root)
 {
-	if (parent != NULL && child != NULL) {
-		child->next = parent->children;
-		parent->children = child;
-		child->parent = parent;
+	if (root != NULL) {
+		if (root->devices != NULL)
+			dlist_destroy(root->devices);
+		if (root->directory != NULL)
+			sysfs_close_directory(root->directory);
+		free(root);
 	}
 }
 
 /**
- * sysfs_open_device_tree: opens root device and all of its children,
- *	creating a tree of devices. Only opens children.
- * @path: sysfs path to devices
- * returns struct sysfs_device and its children with success or NULL with
- *	error.
+ * sysfs_get_root_devices: opens up all the devices under this root device
+ * @root: root device to open devices for
+ * returns dlist of devices with success and NULL with error
  */
-struct sysfs_device *sysfs_open_device_tree(const char *path)
+struct dlist *sysfs_get_root_devices(struct sysfs_root_device *root)
 {
-	struct sysfs_device *rootdev = NULL, *new = NULL;
+	struct sysfs_device *dev = NULL;
 	struct sysfs_directory *cur = NULL;
 
-	if (path == NULL) {
+	if (root == NULL) {
 		errno = EINVAL;
 		return NULL;
 	}
-	rootdev = sysfs_open_device(path);
-	if (rootdev == NULL) {
-		dprintf(stderr, "Error opening root device at %s\n", path);
+	if (root->directory == NULL) {
+		root->directory = open_device_dir(root->path);
+		if (root->directory == NULL)
+			return NULL;
+	}
+		
+	if (root->directory->subdirs == NULL)
+		return 0;
+
+	dlist_for_each_data(root->directory->subdirs, cur,
+			struct sysfs_directory) {
+		dev = sysfs_open_device_tree(cur->path);
+		if (dev == NULL) {
+			dprintf ("Error opening device at %s\n", cur->path);
+			continue;
+		}
+		if (root->devices == NULL)
+			root->devices = dlist_new_with_delete
+				(sizeof(struct sysfs_device), 
+				sysfs_close_dev_tree);
+		dlist_unshift_sorted(root->devices, dev, sort_list);
+	}
+
+	return root->devices;
+}
+
+/**
+ * sysfs_open_root_device: opens sysfs devices root and all of its
+ *	devices.
+ * @name: name of /sys/devices/root to open
+ * returns struct sysfs_root_device if success and NULL with error
+ */
+struct sysfs_root_device *sysfs_open_root_device(const char *name)
+{
+	struct sysfs_root_device *root = NULL;
+	char rootpath[SYSFS_PATH_MAX];
+
+	if (name == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	memset(rootpath, 0, SYSFS_PATH_MAX);
+	if (sysfs_get_mnt_path(rootpath, SYSFS_PATH_MAX) != 0) {
+		dprintf ("Sysfs not supported on this system\n");
+		return NULL;
+	}
+
+	safestrcat(rootpath, "/");
+	safestrcat(rootpath, SYSFS_DEVICES_NAME);
+	safestrcat(rootpath, "/");
+	safestrcat(rootpath, name);
+	if ((sysfs_path_is_dir(rootpath)) != 0) {
+		errno = EINVAL;
+		dprintf("Invalid root device: %s\n", name);
+		return NULL;
+	}
+	root = (struct sysfs_root_device *)calloc
+					(1, sizeof(struct sysfs_root_device));
+	if (root == NULL) {
+		dprintf("calloc failure\n");
 		return NULL;
 	}
-	cur = rootdev->directory->subdirs;
-	while (cur != NULL) {
-		new = sysfs_open_device_tree(cur->path);
-		if (new == NULL) {
-			dprintf(stderr, "Error opening device tree at %s\n",
-				cur->path);
-			sysfs_close_device_tree(rootdev);
+	safestrcpy(root->name, name);
+	safestrcpy(root->path, rootpath);
+	if ((sysfs_remove_trailing_slash(root->path)) != 0) {
+		dprintf("Invalid path to root device %s\n", root->path);
+		sysfs_close_root_device(root);
+		return NULL;
+	}
+	return root;
+}
+
+/**
+ * sysfs_get_device_attributes: returns a dlist of attributes corresponding to
+ * 	the specific device
+ * @device: struct sysfs_device * for which attributes are to be returned
+ */
+struct dlist *sysfs_get_device_attributes(struct sysfs_device *device)
+{
+	if (device == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	if (device->directory == NULL) {
+		device->directory = sysfs_open_directory(device->path);
+		if (device->directory == NULL) 
+			return NULL;
+	}
+	if (device->directory->attributes == NULL) {
+		if ((sysfs_read_dir_attributes(device->directory)) != 0)
+			return NULL;
+	}
+	return (device->directory->attributes);
+}
+
+/**
+ * sysfs_refresh_device_attributes: refreshes the device's list of attributes
+ * @device: sysfs_device whose attributes to refresh
+ *  
+ * NOTE: Upon return, prior references to sysfs_attributes for this device
+ * 		_may_ not be valid
+ *
+ * Returns list of attributes on success and NULL on failure
+ */
+struct dlist *sysfs_refresh_device_attributes(struct sysfs_device *device)
+{
+	if (device == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	if (device->directory == NULL)
+		return (sysfs_get_device_attributes(device));
+
+	if ((sysfs_refresh_dir_attributes(device->directory)) != 0) {
+		dprintf("Error refreshing device attributes\n");
+		return NULL;
+	}
+
+	return (device->directory->attributes);
+}
+
+/**
+ * sysfs_get_device_attr: searches dev's attributes by name
+ * @dev: device to look through
+ * @name: attribute name to get
+ * returns sysfs_attribute reference with success or NULL with error.
+ */
+struct sysfs_attribute *sysfs_get_device_attr(struct sysfs_device *dev,
+						const char *name)
+{
+	struct dlist *attrlist = NULL;
+
+	if (dev == NULL || name == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+	
+	attrlist = sysfs_get_device_attributes(dev);
+	if (attrlist == NULL)
+		return NULL;
+
+	return sysfs_get_directory_attribute(dev->directory, (char *)name);
+}
+
+/**
+ * get_device_absolute_path: looks up the bus the device is on, gets 
+ * 		absolute path to the device
+ * @device: device for which path is needed
+ * @path: buffer to store absolute path
+ * @psize: size of "path"
+ * Returns 0 on success -1 on failure
+ */
+static int get_device_absolute_path(const char *device,	const char *bus, 
+				char *path, size_t psize)
+{
+	char bus_path[SYSFS_PATH_MAX];
+
+	if (device == NULL || path == NULL) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	memset(bus_path, 0, SYSFS_PATH_MAX);
+	if (sysfs_get_mnt_path(bus_path, SYSFS_PATH_MAX) != 0) {
+		dprintf ("Sysfs not supported on this system\n");
+		return -1;
+	}
+	safestrcat(bus_path, "/");
+	safestrcat(bus_path, SYSFS_BUS_NAME);
+	safestrcat(bus_path, "/");
+	safestrcat(bus_path, bus);
+	safestrcat(bus_path, "/");
+	safestrcat(bus_path, SYSFS_DEVICES_NAME);
+	safestrcat(bus_path, "/");
+	safestrcat(bus_path, device);
+	/*
+	 * We now are at /sys/bus/"bus_name"/devices/"device" which is a link.
+	 * Now read this link to reach to the device.
+	 */ 
+	if ((sysfs_get_link(bus_path, path, psize)) != 0) {
+		dprintf("Error getting to device %s\n", device);
+		return -1;
+	}
+	return 0;
+}
+
+/**
+ * sysfs_open_device: open a device by id (use the "bus" subsystem)
+ * @bus: bus the device belongs to
+ * @bus_id: bus_id of the device to open - has to be the "bus_id" in 
+ * 		/sys/bus/xxx/devices
+ * returns struct sysfs_device if found, NULL otherwise
+ * NOTE: 
+ * 1. Use sysfs_close_device to close the device
+ * 2. Bus the device is on must be supplied
+ * 	Use sysfs_find_device_bus to get the bus name
+ */
+struct sysfs_device *sysfs_open_device(const char *bus,	const char *bus_id)
+{
+	char sysfs_path[SYSFS_PATH_MAX];
+	struct sysfs_device *device = NULL;
+
+	if (bus_id == NULL || bus == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+	memset(sysfs_path, 0, SYSFS_PATH_MAX);
+	if ((get_device_absolute_path(bus_id, bus, sysfs_path, 
+						SYSFS_PATH_MAX)) != 0) {
+		dprintf("Error getting to device %s\n", bus_id);
+		return NULL;
+	}
+	
+	device = sysfs_open_device_path(sysfs_path);
+	if (device == NULL) {
+		dprintf("Error opening device %s\n", bus_id);
+		return NULL;
+	}
+
+	return device;
+}
+
+/**
+ * sysfs_get_device_parent: opens up given device's parent and returns a 
+ * 	reference to its sysfs_device
+ * @dev: sysfs_device whose parent is requested
+ * Returns sysfs_device of the parent on success and NULL on failure
+ */
+struct sysfs_device *sysfs_get_device_parent(struct sysfs_device *dev)
+{
+	char ppath[SYSFS_PATH_MAX], *tmp = NULL;
+
+	if (dev == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	if (dev->parent != NULL)
+		return (dev->parent);
+
+	memset(ppath, 0, SYSFS_PATH_MAX);
+	safestrcpy(ppath, dev->path);
+	tmp = strrchr(ppath, '/');
+	if (tmp == NULL) {
+		dprintf("Invalid path to device %s\n", ppath);
+		return NULL;
+	}
+	if (*(tmp + 1) == '\0') {
+		*tmp = '\0';
+		tmp = strrchr(tmp, '/');
+		if (tmp == NULL) {
+			dprintf("Invalid path to device %s\n", ppath);
 			return NULL;
 		}
-		add_device_child_to_parent(rootdev, new);	
-		cur = cur->next;
 	}
+	*tmp = '\0';
+	
+	/*
+	 * All "devices" have the "detach_state" attribute - validate here
+	 */
+	safestrcat(ppath, "/detach_state");
+	if ((sysfs_path_is_file(ppath)) != 0) {
+		dprintf("Device at %s does not have a parent\n", dev->path);
+		return NULL;
+	}
+	tmp = strrchr(ppath, '/');
+	*tmp = '\0';
+	dev->parent = sysfs_open_device_path(ppath);
+	if (dev->parent == NULL) {
+		dprintf("Error opening device %s's parent at %s\n", 
+					dev->bus_id, ppath);
+		return NULL;
+	}
+	return (dev->parent);
+}
 
-	return rootdev;
+/*
+ * sysfs_open_device_attr: open the given device's attribute
+ * @bus: Bus on which to look
+ * @dev_id: device for which attribute is required
+ * @attrname: name of the attribute to look for
+ * Returns struct sysfs_attribute on success and NULL on failure
+ * 
+ * NOTE:
+ * 	A call to sysfs_close_attribute() is required to close
+ * 	the attribute returned and free memory. 
+ */
+struct sysfs_attribute *sysfs_open_device_attr(const char *bus,
+		const char *bus_id, const char *attrib)
+{
+	struct sysfs_attribute *attribute = NULL;
+	char devpath[SYSFS_PATH_MAX];
+	
+	if (bus == NULL || bus_id == NULL || attrib == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	memset(devpath, 0, SYSFS_PATH_MAX);
+	if ((get_device_absolute_path(bus_id, bus, devpath, 
+					SYSFS_PATH_MAX)) != 0) {
+		dprintf("Error getting to device %s\n", bus_id);
+		return NULL;
+	}
+	safestrcat(devpath, "/");
+	safestrcat(devpath, attrib);
+	attribute = sysfs_open_attribute(devpath);
+	if (attribute == NULL) {
+		dprintf("Error opening attribute %s for device %s\n",
+				attrib, bus_id);
+		return NULL;
+	}
+	if ((sysfs_read_attribute(attribute)) != 0) {
+		dprintf("Error reading attribute %s for device %s\n",
+				attrib, bus_id);
+		sysfs_close_attribute(attribute);
+		return NULL;
+	}
+	return attribute;
 }
+