X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=blobdiff_plain;f=libsysfs%2Fsysfs_class.c;h=169600d5fd21f5812a8c68c8a810beea631615e4;hb=5d4754f19521568b775ba7a31465d3af192ce382;hp=9d7d8b222711e541a1792827375b73ba7cd2954a;hpb=070f54223f66490e9d25719c495e074f77da8985;p=elogind.git

diff --git a/libsysfs/sysfs_class.c b/libsysfs/sysfs_class.c
index 9d7d8b222..169600d5f 100644
--- a/libsysfs/sysfs_class.c
+++ b/libsysfs/sysfs_class.c
@@ -3,7 +3,7 @@
  *
  * Generic class 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
@@ -23,6 +23,28 @@
 #include "libsysfs.h"
 #include "sysfs.h"
 
+static void sysfs_close_cls_dev(void *dev)
+{
+	sysfs_close_class_device((struct sysfs_class_device *)dev);
+}
+
+/**
+ * class_name_equal: compares class_devices' name
+ * @a: class_name looking for
+ * @b: sysfs_class_device being compared
+ */
+static int class_name_equal(void *a, void *b)
+{
+	if (a == NULL || b == NULL)
+		return 0;
+
+	if (strcmp(((unsigned char *)a), ((struct sysfs_class_device *)b)->name)
+		== 0)
+		return 1;
+
+	return 0;
+}
+
 /**
  * sysfs_close_class_device: closes a single class device.
  * @dev: class device to close.
@@ -36,6 +58,8 @@ void sysfs_close_class_device(struct sysfs_class_device *dev)
 			sysfs_close_device(dev->sysdevice);
 		if (dev->driver != NULL)
 			sysfs_close_driver(dev->driver);
+		if (dev->parent != NULL)
+			sysfs_close_class_device(dev->parent);
 		free(dev);
 	}
 }
@@ -46,15 +70,11 @@ void sysfs_close_class_device(struct sysfs_class_device *dev)
  */
 void sysfs_close_class(struct sysfs_class *cls)
 {
-	struct sysfs_class_device *cur = NULL, *next = NULL;
-
 	if (cls != NULL) {
 		if (cls->directory != NULL)
 			sysfs_close_directory(cls->directory);
-		for (cur = cls->devices; cur != NULL; cur = next) {
-			next = cur->next;
-			sysfs_close_class_device(cur);
-		}
+		if (cls->devices != NULL) 
+			dlist_destroy(cls->devices);
 		free(cls);
 	}
 }
@@ -78,44 +98,35 @@ static struct sysfs_class *alloc_class(void)
 	return (struct sysfs_class *)calloc(1, sizeof(struct sysfs_class));
 }
 
-/**
- * open_class_dir: opens up sysfs class directory
- * returns sysfs_directory struct with success and NULL with error
+/** 
+ * set_classdev_classname: Grabs classname from path
+ * @cdev: class device to set
+ * Returns nothing
  */
-static struct sysfs_directory *open_class_dir(const char *name)
+static void set_classdev_classname(struct sysfs_class_device *cdev)
 {
-	struct sysfs_directory *classdir = NULL;
-	char classpath[SYSFS_PATH_MAX];
+	unsigned char *c = NULL, *e = NULL;
+	int count = 0;
 
-	if (name == NULL) {
-		errno = EINVAL;
-		return NULL;
+	c = strstr(cdev->path, SYSFS_CLASS_NAME);
+	if (c == NULL) {
+		c = strstr(cdev->path, SYSFS_BLOCK_NAME);
+	} else {
+		c = strstr(c, "/");
 	}
 
-	memset(classpath, 0, SYSFS_PATH_MAX);
-	if ((sysfs_get_mnt_path(classpath, SYSFS_PATH_MAX)) != 0) {
-		dprintf(stderr, "Sysfs not supported on this system\n");
-		return NULL;
-	}
-
-	strcat(classpath, SYSFS_CLASS_DIR);
-	strcat(classpath, "/");
-	strcat(classpath, name);
-	classdir = sysfs_open_directory(classpath);
-	if (classdir == NULL) {
-		errno = EINVAL;
-		dprintf(stderr,"Class %s not supported on this system\n",
-			name);
-		return NULL;
-	}
-	if ((sysfs_read_directory(classdir)) != 0) {
-		dprintf(stderr, "Error reading %s class dir %s\n", name, 
-			classpath);
-		sysfs_close_directory(classdir);
-		return NULL;
+	if (c == NULL)
+		strcpy(cdev->classname, SYSFS_UNKNOWN);
+	else {
+		if (*c == '/')
+			c++;
+		e = c;
+		while (e != NULL && *e != '/' && *e != '\0') {
+			e++;
+			count++;
+		}
+		strncpy(cdev->classname, c, count);
 	}
-
-	return classdir;
 }
 
 /**
@@ -123,151 +134,512 @@ static struct sysfs_directory *open_class_dir(const char *name)
  * @path: path to class device.
  * returns struct sysfs_class_device with success and NULL with error.
  */
-struct sysfs_class_device *sysfs_open_class_device(const char *path)
+struct sysfs_class_device *sysfs_open_class_device(const unsigned char *path)
 {
 	struct sysfs_class_device *cdev = NULL;
-	struct sysfs_directory *dir = NULL, *cur = NULL;
-	struct sysfs_dlink *curl = NULL;
-	struct sysfs_device *sdev = NULL;
-	struct sysfs_driver *drv = NULL;
-	char temp[SYSFS_NAME_LEN];
 
 	if (path == NULL) {
 		errno = EINVAL;
 		return NULL;
 	}
+	if ((sysfs_path_is_dir(path)) != 0) {
+		dprintf("%s is not a valid path to a class device\n", path);
+		return NULL;
+	}
 	cdev = alloc_class_device();
 	if (cdev == NULL) {
-		perror("malloc");
+		dprintf("calloc failed\n");
 		return NULL;
 	}
-	memset(temp, 0, SYSFS_NAME_LEN);
-	if ((sysfs_get_name_from_path(path, temp, SYSFS_NAME_LEN)) != 0) {
+	if ((sysfs_get_name_from_path(path, cdev->name, SYSFS_NAME_LEN)) != 0) {
 		errno = EINVAL;
-		dprintf(stderr, "Invalid class device path %s\n", path);
+		dprintf("Error getting class device name\n");
 		sysfs_close_class_device(cdev);
 		return NULL;
 	}
-	strcpy(cdev->name, temp);
 
-	dir = sysfs_open_directory(path);
-	if (dir == NULL) {
-		dprintf(stderr, "Error opening class device at %s\n", path);
-		sysfs_close_class_device(cdev);
-		return NULL;
-	}
-	if ((sysfs_read_directory(dir)) != 0) {
-		dprintf(stderr, "Error reading class device at %s\n", path);
-		sysfs_close_directory(dir);
-		sysfs_close_class_device(cdev);
-		return NULL;
-	}
-	cdev->directory = dir;
-
-	cur = cdev->directory->subdirs;
-	while(cur != NULL) {
-		sysfs_read_directory(cur);
-		cur = cur->next;
-	}
-	/* get driver and device, if implemented */
-	curl = cdev->directory->links;
-	while (curl != NULL) {
-		if (strncmp(curl->name, SYSFS_DEVICES_NAME, 6) == 0) {
-			sdev = sysfs_open_device(curl->target->path);
-			if (sdev != NULL) {
-				cdev->sysdevice = sdev;
-				if (cdev->driver != NULL) 
-					sdev->driver = cdev->driver;
-			}
-		} else if (strncmp(curl->name, SYSFS_DRIVERS_NAME, 6) == 0) {
-			drv = sysfs_open_driver(curl->target->path);
-			if (drv != NULL) {
-				cdev->driver = drv;
-				if (cdev->sysdevice != NULL) 
-					drv->device = cdev->sysdevice;
-			}
-		}
-		curl = curl->next;
-	}
-	return cdev;
-}
+	strcpy(cdev->path, path);
+	set_classdev_classname(cdev);
 
-/**
- * add_dev_to_class: adds a class device to class list
- * @class: class to add the device
- * @dev: device to add
- */
-static void add_dev_to_class(struct sysfs_class *cls, 
-					struct sysfs_class_device *dev)
-{
-	if (cls != NULL && dev != NULL) {
-		dev->next = cls->devices;
-		cls->devices = dev;
-	}
+	return cdev;
 }
 
 /**
- * get_all_class_devices: gets all devices for class
+ * sysfs_get_class_devices: gets all devices for class
  * @class: class to get devices for
- * returns 0 with success and -1 with failure
+ * returns dlist of class_devices with success and NULL with error
  */
-static int get_all_class_devices(struct sysfs_class *cls)
+struct dlist *sysfs_get_class_devices(struct sysfs_class *cls)
 {
 	struct sysfs_class_device *dev = NULL;
-	struct sysfs_directory *cur = NULL, *next = NULL;
+	struct sysfs_directory *cur = NULL;
 
-	if (cls == NULL || cls->directory == NULL) {
+	if (cls == NULL) {
 		errno = EINVAL;
-		return -1;
+		return NULL;
 	}
-	for (cur = cls->directory->subdirs; cur != NULL; cur = next) {
-		next = cur->next;
+	if (cls->directory == NULL) {
+		cls->directory = sysfs_open_directory(cls->path);
+		if (cls->directory == NULL) 
+			return NULL;
+	}
+
+	if ((sysfs_read_dir_subdirs(cls->directory) != 0) 
+	    || cls->directory->subdirs == NULL)
+		return NULL;
+
+	dlist_for_each_data(cls->directory->subdirs, cur, 
+			struct sysfs_directory) {
 		dev = sysfs_open_class_device(cur->path);
 		if (dev == NULL) {
-			dprintf(stderr, "Error opening device at %s\n",
-				cur->path);
+			dprintf("Error opening device at %s\n",	cur->path);
 			continue;
 		}
-		add_dev_to_class(cls, dev);
+		if (cls->devices == NULL)
+			cls->devices = dlist_new_with_delete
+					(sizeof(struct sysfs_class_device),
+					 		sysfs_close_cls_dev);
+		dlist_unshift(cls->devices, dev);
 	}
-			
-	return 0;
+	return cls->devices;
 }
 
 /**
  * sysfs_open_class: opens specific class and all its devices on system
  * returns sysfs_class structure with success or NULL with error.
  */
-struct sysfs_class *sysfs_open_class(const char *name)
+struct sysfs_class *sysfs_open_class(const unsigned char *name)
 {
 	struct sysfs_class *cls = NULL;
-	struct sysfs_directory *classdir = NULL;
+	unsigned char classpath[SYSFS_PATH_MAX];
 
 	if (name == NULL) {
 		errno = EINVAL;
 		return NULL;
 	}
 
+	memset(classpath, 0, SYSFS_PATH_MAX);
+        if ((sysfs_get_mnt_path(classpath, SYSFS_PATH_MAX)) != 0) {
+                dprintf("Sysfs not supported on this system\n");
+                return NULL;
+        }
+
+	if (sysfs_trailing_slash(classpath) == 0)
+		strcat(classpath, "/");
+
+	/* 
+	 * We shall now treat "block" also as a class. Hence, check here
+	 * if "name" is "block" and proceed accordingly
+	 */
+	if (strcmp(name, SYSFS_BLOCK_NAME) == 0) {
+		strcat(classpath, SYSFS_BLOCK_NAME);
+	} else {
+		strcat(classpath, SYSFS_CLASS_NAME);
+		strcat(classpath, "/");
+		strcat(classpath, name);
+	}
+	if ((sysfs_path_is_dir(classpath)) != 0) {
+		dprintf("Class %s not found on the system\n", name);
+		return NULL;
+	}
+
 	cls = alloc_class();
 	if (cls == NULL) {
-		perror("malloc");
+		dprintf("calloc failed\n");
 		return NULL;
 	}
 	strcpy(cls->name, name);	
-	classdir = open_class_dir(name);
-	if (classdir == NULL) {
-		dprintf(stderr,
-			"Invalid class, %s not supported on this system\n",
-			name);
-		sysfs_close_class(cls);
+	strcpy(cls->path, classpath);
+	
+	return cls;
+}
+
+/**
+ * sysfs_get_class_device: Get specific class device using the device's id
+ * @class: class to find device on
+ * @name: class name of the device
+ */ 
+struct sysfs_class_device *sysfs_get_class_device(struct sysfs_class *class,
+					unsigned char *name)
+{
+	struct dlist *devlist = NULL;
+	
+	if (class == NULL || name == NULL) {
+		errno = EINVAL;
 		return NULL;
 	}
-	cls->directory = classdir;
-	if ((get_all_class_devices(cls)) != 0) {
-		dprintf(stderr, "Error reading %s class devices\n", name);
-		sysfs_close_class(cls);
+
+	if (class->devices == NULL) {
+		class->devices = sysfs_get_class_devices(class);
+		if (devlist == NULL) 
+			return NULL;
+	}
+	return (struct sysfs_class_device *)dlist_find_custom(class->devices,
+			name, class_name_equal);
+}
+
+/**
+ * sysfs_get_classdev_device: returns the sysfs_device corresponding to
+ * 		sysfs_class_device, if present
+ * @clsdev: class device whose sysfs_device is required
+ * Returns sysfs_device on success, NULL on error or if device is not
+ * implemented
+ */ 
+struct sysfs_device *sysfs_get_classdev_device
+			(struct sysfs_class_device *clsdev)
+{
+	struct sysfs_link *devlink = NULL;
+	
+	if (clsdev == NULL) {
+		errno = EINVAL;
 		return NULL;
 	}
+	
+	if (clsdev->sysdevice != NULL)
+		return (clsdev->sysdevice);
+	
+	if (clsdev->directory == NULL) {
+		clsdev->directory = sysfs_open_directory(clsdev->path);
+		if (clsdev->directory == NULL)
+			return NULL;
+	}
+	devlink = sysfs_get_directory_link(clsdev->directory, "device");
+	if (devlink == NULL) 
+		return NULL;
 
-	return cls;
+	clsdev->sysdevice = sysfs_open_device(devlink->target);
+	if (clsdev->sysdevice == NULL)
+		return NULL;
+	if (clsdev->driver != NULL) 
+		strcpy(clsdev->sysdevice->driver_name, clsdev->driver->name);
+
+	return (clsdev->sysdevice);
+}
+				
+/**
+ * sysfs_get_classdev_driver: returns the sysfs_driver corresponding to
+ * 		sysfs_class_device, if present
+ * @clsdev: class device whose sysfs_device is required
+ * Returns sysfs_driver on success, NULL on error or if driver is not
+ * implemented
+ */ 
+struct sysfs_driver *sysfs_get_classdev_driver
+			(struct sysfs_class_device *clsdev)
+{
+	struct sysfs_link *drvlink = NULL;
+	
+	if (clsdev == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+	
+	if (clsdev->driver != NULL)
+		return (clsdev->driver);
+	
+	if (clsdev->directory == NULL) {
+		clsdev->directory = sysfs_open_directory(clsdev->path);
+		if (clsdev->directory == NULL)
+			return NULL;
+	}
+	drvlink = sysfs_get_directory_link(clsdev->directory, "driver");
+	if (drvlink != NULL) {
+		clsdev->driver = sysfs_open_driver(drvlink->target);
+		if (clsdev->driver == NULL)
+			return NULL;
+			
+	}
+	return (clsdev->driver);
+}
+	
+/* 
+ * get_blockdev_parent: Get the parent class device for a "block" subsystem 
+ * 		device if present
+ * @clsdev: block subsystem class device whose parent needs to be found
+ * Returns 0 on success and 1 on error
+ */
+static int get_blockdev_parent(struct sysfs_class_device *clsdev)
+{
+	unsigned char parent_path[SYSFS_PATH_MAX], value[256], *c = NULL;
+	
+	memset(parent_path, 0, SYSFS_PATH_MAX);
+	strcpy(parent_path, clsdev->path);
+
+	c = strstr(parent_path, SYSFS_BLOCK_NAME);
+	if (c == NULL) {
+		dprintf("Class device %s does not belong to BLOCK subsystem",
+				clsdev->name);
+		return 1;
+	}
+	
+	c += strlen(SYSFS_BLOCK_NAME);
+	if (*c == '/')
+		c++;
+	else
+		goto errout;
+	
+	/* validate whether the given class device is a partition or not */ 
+	if ((strncmp(c, clsdev->name, strlen(clsdev->name))) == 0) {
+		dprintf("%s not a partition\n", clsdev->name);
+		return 1;
+	}
+	c = strchr(c, '/');
+	if (c == NULL) 
+		goto errout;
+	*c = '\0';
+	
+	/* Now validate if the parent has the "dev" attribute */
+	memset(value, 0, 256);
+	strcat(parent_path, "/dev");
+	if ((sysfs_read_attribute_value(parent_path, value, 256)) != 0) {
+		dprintf("Block device %s does not have a parent\n", 
+							clsdev->name);
+		return 1;
+	}
+		
+	c = strrchr(parent_path, '/');
+	if (c == NULL)
+		goto errout;
+
+	*c = '\0';
+	clsdev->parent = sysfs_open_class_device(parent_path);
+	if (clsdev->parent == NULL) {
+		dprintf("Error opening the parent class device at %s\n", 
+								parent_path);
+		return 1;
+	}
+	return 0;
+
+errout:
+	dprintf("Invalid path %s\n", clsdev->path);
+	return 1;
+}
+
+/**
+ * sysfs_get_classdev_parent: Retrieves the parent of a class device. 
+ * 	eg., when working with hda1, this function can be used to retrieve the
+ * 		sysfs_class_device for hda
+ * 		
+ * @clsdev: class device whose parent details are required.
+ * Returns sysfs_class_device of the parent on success, NULL on failure
+ */ 
+struct sysfs_class_device *sysfs_get_classdev_parent
+				(struct sysfs_class_device *clsdev)
+{
+	if (clsdev == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+	if (clsdev->parent != NULL)
+		return (clsdev->parent);
+	
+	/* 
+	 * As of now, only block devices have a parent child heirarchy in sysfs
+	 * We do not know, if, in the future, more classes will have a similar
+	 * structure. Hence, we now call a specialized function for block and
+	 * later we can add support functions for other subsystems as required.
+	 */ 
+	if (!(strcmp(clsdev->classname, SYSFS_BLOCK_NAME))) {
+		if ((get_blockdev_parent(clsdev)) == 0) 
+			return (clsdev->parent);
+	}
+	return NULL;
+}
+
+/**
+ * get_classdev_path: given the class and a device in the class, return the
+ * 		absolute path to the device
+ * @classname: name of the class
+ * @clsdev: the class device
+ * @path: buffer to return path
+ * @psize: size of "path"
+ * Returns 0 on SUCCESS or -1 on error
+ */
+static int get_classdev_path(const unsigned char *classname, 
+		const unsigned char *clsdev, unsigned char *path, size_t len)
+{
+	if (classname == NULL || clsdev == NULL || path == NULL) {
+		errno = EINVAL;
+		return -1;
+	}
+        if (sysfs_get_mnt_path(path, len) != 0) {
+                dprintf("Error getting sysfs mount path\n");
+                return -1;
+	}
+
+	if (sysfs_trailing_slash(path) == 0)
+		strcat(path, "/");
+
+	if (strcmp(classname, SYSFS_BLOCK_NAME) == 0) {
+		strcat(path, SYSFS_BLOCK_NAME);
+	} else {
+		strcat(path, SYSFS_CLASS_NAME);
+		strcat(path, "/");
+		strcat(path, classname);
+	}
+	strcat(path, "/");
+	strcat(path, clsdev);
+	return 0;
+}
+
+/**
+ * sysfs_open_class_device_by_name: Locates a specific class_device and returns it.
+ * Class_device must be closed using sysfs_close_class_device
+ * @classname: Class to search
+ * @name: name of the class_device
+ * 
+ * NOTE:
+ * 	Call sysfs_close_class_device() to close the class device
+ */
+struct sysfs_class_device *sysfs_open_class_device_by_name
+		(const unsigned char *classname, const unsigned char *name)
+{
+	unsigned char devpath[SYSFS_PATH_MAX];
+	struct sysfs_class_device *cdev = NULL;
+
+	if (classname == NULL || name == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+	
+	memset(devpath, 0, SYSFS_PATH_MAX);
+	if ((get_classdev_path(classname, name, devpath, 
+					SYSFS_PATH_MAX)) != 0) {
+		dprintf("Error getting to device %s on class %s\n",
+							name, classname);
+		return NULL;
+	}
+	
+	cdev = sysfs_open_class_device(devpath);
+	if (cdev == NULL) {
+		dprintf("Error getting class device %s from class %s\n",
+				name, classname);
+		return NULL;
+	}
+	return cdev;
+}
+
+/**
+ * sysfs_get_classdev_attributes: returns a dlist of attributes for
+ * 	the requested class_device
+ * @cdev: sysfs_class_dev for which attributes are needed
+ * returns a dlist of attributes if exists, NULL otherwise
+ */
+struct dlist *sysfs_get_classdev_attributes(struct sysfs_class_device *cdev)
+{
+	if (cdev == NULL)
+		return NULL;
+
+	if (cdev->directory == NULL) {
+		cdev->directory = sysfs_open_directory(cdev->path);
+		if (cdev->directory == NULL) 
+			return NULL;
+	}
+	if (cdev->directory->attributes == NULL) {
+		if ((sysfs_read_dir_attributes(cdev->directory)) != 0) {
+			dprintf("Error reading attributes for directory %s\n",
+							cdev->directory->path);
+			return NULL;
+		}
+	} else {
+		if ((sysfs_path_is_dir(cdev->path)) != 0) {
+			dprintf("Class device at %s no longer exists\n", 
+							cdev->path);
+			return NULL;
+		}
+		if ((sysfs_refresh_attributes
+					(cdev->directory->attributes)) != 0) {
+			dprintf("Error refreshing classdev attributes\n");
+			return NULL;
+		}
+	}
+	return (cdev->directory->attributes);
+}
+
+/**
+ * sysfs_get_classdev_attr: searches class device's attributes by name
+ * @clsdev: class device to look through
+ * @name: attribute name to get
+ * returns sysfs_attribute reference with success or NULL with error
+ */
+struct sysfs_attribute *sysfs_get_classdev_attr
+		(struct sysfs_class_device *clsdev, const unsigned char *name)
+{
+	struct sysfs_attribute *cur = NULL;
+	struct sysfs_directory *sdir = NULL;
+	struct dlist *attrlist = NULL;
+	
+	if (clsdev == NULL || name == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+	/* 
+	 * First, see if it's in the current directory. Then look at 
+	 * subdirs since class devices can have subdirs of attributes.
+	 */ 
+	attrlist = sysfs_get_classdev_attributes(clsdev);
+	if (attrlist == NULL)
+		return NULL;
+	cur = sysfs_get_directory_attribute(clsdev->directory,
+						(unsigned char *)name);
+	if (cur != NULL)
+		return cur;
+
+	if (clsdev->directory->subdirs == NULL) 
+		if ((sysfs_read_dir_subdirs(clsdev->directory)) != 0 ||
+		    clsdev->directory->subdirs == NULL) 
+			return NULL;
+
+	dlist_for_each_data(clsdev->directory->subdirs, sdir,
+				struct sysfs_directory) {
+		cur = sysfs_get_directory_attribute(sdir, 
+						(unsigned char *)name);
+		if (cur != NULL)
+			return cur;
+	}
+		
+	return NULL;
+}
+
+/**
+ * sysfs_open_classdev_attr: read an attribute for a given class device
+ * @classname: name of the class on which to look
+ * @dev: class device name for which the attribute has to be read
+ * @attrib: attribute to read
+ * Returns sysfs_attribute * on SUCCESS and NULL on error
+ * 
+ * NOTE:
+ * 	A call to sysfs_close_attribute() is required to close the
+ * 	attribute returned and to free memory
+ */
+struct sysfs_attribute *sysfs_open_classdev_attr(const unsigned char *classname,
+		const unsigned char *dev, const unsigned char *attrib)
+{
+	struct sysfs_attribute *attribute = NULL;
+	unsigned char path[SYSFS_PATH_MAX];
+
+	if (classname == NULL || dev == NULL || attrib == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+	memset(path, 0, SYSFS_PATH_MAX);
+	if ((get_classdev_path(classname, dev, path, SYSFS_PATH_MAX)) != 0) {
+		dprintf("Error getting to device %s on class %s\n",
+						dev, classname);
+		return NULL;
+	}
+	strcat(path, "/");
+	strcat(path, attrib);
+	attribute = sysfs_open_attribute(path);
+	if (attribute == NULL) {
+		dprintf("Error opening attribute %s on class device %s\n",
+				attrib, dev);
+		return NULL;
+	}
+	if ((sysfs_read_attribute(attribute)) != 0) {
+		dprintf("Error reading attribute %s for class device %s\n",
+				attrib, dev);
+		sysfs_close_attribute(attribute);
+		return NULL;
+	}
+	return attribute;
 }