X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=libsysfs%2Fsysfs_device.c;h=66d5f9aef7c71b65b9e9272b053eb4bac8a21525;hp=89704dcd8041092abf6b9f8e6c6362a1bf43ba84;hb=ac28b86d631f23b5df74dbeb33e76a2b3f5d88bb;hpb=fe3fe3b29ffbc7d0ce7dca6a371da31d8b3ff7f8

diff --git a/libsysfs/sysfs_device.c b/libsysfs/sysfs_device.c
index 89704dcd8..66d5f9aef 100644
--- a/libsysfs/sysfs_device.c
+++ b/libsysfs/sysfs_device.c
@@ -23,6 +23,67 @@
 #include "libsysfs.h"
 #include "sysfs.h"
 
+/**
+ * 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.
+ */
+static int get_device_bus(struct sysfs_device *dev)
+{
+	unsigned char subsys[SYSFS_NAME_LEN], path[SYSFS_PATH_MAX];
+	unsigned 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);
+	strcat(subsys, "/");
+	strcpy(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);
+			strcpy(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';
+			strcat(path, "/");
+			strcat(path, SYSFS_BUS_NAME);
+			strcat(path, "/");
+			strcat(path, bus);
+			strcat(path, "/");
+			strcat(path, SYSFS_DEVICES_NAME);
+			strcat(path, "/");
+			strcat(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))) {
+					strcpy(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.
@@ -43,14 +104,6 @@ static void sysfs_close_device_tree(struct sysfs_device *devroot)
 	}
 }
 
-/**
- * sysfs_del_device: routine for dlist integration
- */
-static void sysfs_del_device(void *dev)
-{
-	sysfs_close_device((struct sysfs_device *)dev);
-}
-
 /**
  * sysfs_close_dev_tree: routine for dlist integration
  */
@@ -66,6 +119,8 @@ static void sysfs_close_dev_tree(void *dev)
 void sysfs_close_device(struct sysfs_device *dev)
 {
 	if (dev != NULL) {
+		if (dev->parent != NULL)
+			sysfs_close_device(dev->parent);
 		if (dev->directory != NULL)
 			sysfs_close_directory(dev->directory);
 		if (dev->children != NULL && dev->children->count == 0)
@@ -84,72 +139,73 @@ 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 unsigned char *name)
+static struct sysfs_directory *open_device_dir(const unsigned char *path)
 {
-	struct sysfs_attribute *cur = NULL;
+	struct sysfs_directory *rdir = NULL;
 
-	if (dev == NULL || dev->directory == NULL 
-	    || dev->directory->attributes == NULL || name == NULL) {
+	if (path == NULL) {
 		errno = EINVAL;
 		return NULL;
 	}
-	
-	cur = sysfs_get_directory_attribute(dev->directory, 
-			(unsigned char *)name);
-	if (cur != NULL)
-		return cur;
 
-	return NULL;
+	rdir = sysfs_open_directory(path);
+	if (rdir == NULL) {
+		errno = EINVAL;
+		dprintf ("Device %s not supported on this system\n", path);
+		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 unsigned char *path)
+struct sysfs_device *sysfs_open_device_path(const unsigned char *path)
 {
 	struct sysfs_device *dev = NULL;
-	struct sysfs_directory *sdir = 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("Error allocating device at %s\n", path);
 		return NULL;
 	}
-	sdir = sysfs_open_directory(path);
-	if (sdir == NULL) {
-		dprintf("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("Error reading device directory at %s\n", path);
-		sysfs_close_directory(sdir);
-		sysfs_close_device(dev);
-		return NULL;
-	}
-	dev->directory = sdir;
-	strcpy(dev->bus_id, sdir->name);
-	strcpy(dev->path, sdir->path);
-
+	strcpy(dev->path, path);
 	/* 
 	 * 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.
 	 */
-	strncpy(dev->name, sdir->name, SYSFS_NAME_LEN);
+	strncpy(dev->name, dev->bus_id, SYSFS_NAME_LEN);
+	
+	if (get_device_bus(dev) != 0)
+		strcpy(dev->bus, SYSFS_UNKNOWN);
 
 	return dev;
 }
@@ -170,11 +226,16 @@ static struct sysfs_device *sysfs_open_device_tree(const unsigned char *path)
 		errno = EINVAL;
 		return NULL;
 	}
-	rootdev = sysfs_open_device(path);
+	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) {
@@ -188,7 +249,7 @@ static struct sysfs_device *sysfs_open_device_tree(const unsigned char *path)
 			if (rootdev->children == NULL)
 				rootdev->children = dlist_new_with_delete
 					(sizeof(struct sysfs_device),
-					sysfs_del_device);
+					sysfs_close_dev_tree);
 			dlist_unshift(rootdev->children, new);
 		}
 	}
@@ -212,60 +273,25 @@ void sysfs_close_root_device(struct sysfs_root_device *root)
 }
 
 /**
- * open_root_device_dir: opens up sysfs_directory for specific root dev
- * @name: name of root
- * returns struct sysfs_directory with success and NULL with error
- */
-static struct sysfs_directory *open_root_device_dir(const unsigned char *name)
-{
-	struct sysfs_directory *rdir = NULL;
-	unsigned 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;
-	}
-
-	strcat(rootpath, SYSFS_DEVICES_DIR);
-	strcat(rootpath, "/");
-	strcat(rootpath, name);
-	rdir = sysfs_open_directory(rootpath);
-	if (rdir == NULL) {
-		errno = EINVAL;
-		dprintf ("Root device %s not supported on this system\n",
-			name);
-		return NULL;
-	}
-	if (sysfs_read_directory(rdir) != 0) {
-		dprintf ("Error reading %s root device at dir %s\n", name,
-			rootpath);
-		sysfs_close_directory(rdir);
-		return NULL;
-	}
-	
-	return rdir;
-}
-
-/**
- * get_all_root_devices: opens up all the devices under this root device
+ * sysfs_get_root_devices: opens up all the devices under this root device
  * @root: root device to open devices for
- * returns 0 with success and -1 with error
+ * returns dlist of devices with success and NULL with error
  */
-static int get_all_root_devices(struct sysfs_root_device *root)
+struct dlist *sysfs_get_root_devices(struct sysfs_root_device *root)
 {
 	struct sysfs_device *dev = NULL;
 	struct sysfs_directory *cur = NULL;
 
-	if (root == NULL || root->directory == NULL) {
+	if (root == NULL) {
 		errno = EINVAL;
-		return -1;
+		return NULL;
+	}
+	if (root->directory == NULL) {
+		root->directory = open_device_dir(root->path);
+		if (root->directory == NULL)
+			return NULL;
 	}
+		
 	if (root->directory->subdirs == NULL)
 		return 0;
 
@@ -283,7 +309,7 @@ static int get_all_root_devices(struct sysfs_root_device *root)
 		dlist_unshift(root->devices, dev);
 	}
 
-	return 0;
+	return root->devices;
 }
 
 /**
@@ -295,33 +321,37 @@ static int get_all_root_devices(struct sysfs_root_device *root)
 struct sysfs_root_device *sysfs_open_root_device(const unsigned char *name)
 {
 	struct sysfs_root_device *root = NULL;
-	struct sysfs_directory *rootdir = NULL;
+	unsigned char rootpath[SYSFS_PATH_MAX];
 
 	if (name == NULL) {
 		errno = EINVAL;
 		return NULL;
 	}
 
-	root = (struct sysfs_root_device *)calloc
-					(1, sizeof(struct sysfs_root_device));
-	if (root == NULL) {
-		dprintf("calloc failure\n");
+	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;
 	}
-	rootdir = open_root_device_dir(name);
-	if (rootdir == NULL) {
-		dprintf ("Invalid root device, %s not supported\n", name);
-		sysfs_close_root_device(root);
+
+	if (sysfs_trailing_slash(rootpath) == 0)
+		strcat(rootpath, "/");
+	strcat(rootpath, SYSFS_DEVICES_NAME);
+	strcat(rootpath, "/");
+	strcat(rootpath, name);
+	if ((sysfs_path_is_dir(rootpath)) != 0) {
+		errno = EINVAL;
+		dprintf("Invalid root device: %s\n", name);
 		return NULL;
 	}
-	strcpy(root->path, rootdir->path);
-	root->directory = rootdir;
-	if (get_all_root_devices(root) != 0) {
-		dprintf ("Error retrieving devices for root %s\n", name);
-		sysfs_close_root_device(root);
+	root = (struct sysfs_root_device *)calloc
+					(1, sizeof(struct sysfs_root_device));
+	if (root == NULL) {
+		dprintf("calloc failure\n");
 		return NULL;
 	}
-
+	strcpy(root->name, name);
+	strcpy(root->path, rootpath);
 	return root;
 }
 
@@ -332,59 +362,56 @@ struct sysfs_root_device *sysfs_open_root_device(const unsigned char *name)
  */
 struct dlist *sysfs_get_device_attributes(struct sysfs_device *device)
 {
-	if (device == NULL || device->directory == NULL) 
+	if (device == NULL) 
 		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;
+	} else {
+		if ((sysfs_path_is_dir(device->path)) != 0) {
+			dprintf("Device at %s no longer exists", device->path);
+			return NULL;
+		}
+		if ((sysfs_refresh_attributes
+				(device->directory->attributes)) != 0) {
+			dprintf("Error refreshing device attributes\n");
+			return NULL;
+		}
+	}
 	return (device->directory->attributes);
 }
 
 /**
- * sysfs_open_device_by_id: open a device by id (use the "bus" subsystem)
- * @bus_id: bus_id of the device to open - has to be the "bus_id" in 
- * 		/sys/bus/xxx/devices
- * @bus: bus the device belongs to
- * @bsize: size of the bus buffer
- * 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
+ * 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_device *sysfs_open_device_by_id(const unsigned char *bus_id, 
-		const unsigned char *bus, size_t bsize)
+struct sysfs_attribute *sysfs_get_device_attr(struct sysfs_device *dev,
+						const unsigned char *name)
 {
-	char sysfs_path[SYSFS_PATH_MAX], device_path[SYSFS_PATH_MAX];
-	struct sysfs_device *device = NULL;
+	struct sysfs_attribute *cur = NULL;
+	struct dlist *attrlist = NULL;
 
-	if (bus_id == NULL || bus == NULL) {
+	if (dev == NULL || name == NULL) {
 		errno = EINVAL;
 		return NULL;
 	}
-	memset(sysfs_path, 0, SYSFS_PATH_MAX);
-	if ((sysfs_get_mnt_path(sysfs_path, SYSFS_PATH_MAX)) != 0) {
-		dprintf("Error getting sysfs mount path\n");
-		return NULL;
-	}
-	strcat(sysfs_path, SYSFS_BUS_DIR);
-	strcat(sysfs_path, "/");
-	strncat(sysfs_path, bus, bsize);
-	strcat(sysfs_path, SYSFS_DEVICES_DIR);
-	strcat(sysfs_path, "/");
-	strcat(sysfs_path, bus_id);
 
-	/* devices under /sys/bus/xxx/devices are links to devices subsystem */
-	if ((sysfs_get_link(sysfs_path, device_path, SYSFS_PATH_MAX)) < 0) {
-		dprintf("Error getting device path\n");
+	attrlist = sysfs_get_device_attributes(dev);
+	if (attrlist == NULL)
 		return NULL;
-	}
-	
-	device = sysfs_open_device(device_path);
-	if (device == NULL) {
-		dprintf("Error opening device %s\n", bus_id);
-		return NULL;
-	}
 
-	return device;
+	cur = sysfs_get_directory_attribute(dev->directory, 
+			(unsigned char *)name);
+
+	return cur;
 }
 
 /**
@@ -395,30 +422,28 @@ struct sysfs_device *sysfs_open_device_by_id(const unsigned char *bus_id,
  * @psize: size of "path"
  * Returns 0 on success -1 on failure
  */
-static int get_device_absolute_path(const unsigned char *device, 
-					unsigned char *path, size_t psize)
+static int get_device_absolute_path(const unsigned char *device,
+		const unsigned char *bus, unsigned char *path, size_t psize)
 {
-	unsigned char bus_name[SYSFS_NAME_LEN], bus_path[SYSFS_PATH_MAX];
+	unsigned char bus_path[SYSFS_PATH_MAX];
 
 	if (device == NULL || path == NULL) {
 		errno = EINVAL;
 		return -1;
 	}
 
-	memset(bus_name, 0, SYSFS_NAME_LEN);
-	memset(bus_path, 0, SYSFS_NAME_LEN);
-	if ((sysfs_find_device_bus(device, bus_name, SYSFS_NAME_LEN)) != 0) {
-		dprintf("Device %s not found\n", device);
-		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;
 	}
-	strcat(bus_path, SYSFS_BUS_DIR);
+	if (sysfs_trailing_slash(bus_path) == 0)
+		strcat(bus_path, "/");
+	strcat(bus_path, SYSFS_BUS_NAME);
 	strcat(bus_path, "/");
-	strcat(bus_path, bus_name);
-	strcat(bus_path, SYSFS_DEVICES_DIR);
+	strcat(bus_path, bus);
+	strcat(bus_path, "/");
+	strcat(bus_path, SYSFS_DEVICES_NAME);
 	strcat(bus_path, "/");
 	strcat(bus_path, device);
 	/*
@@ -433,106 +458,138 @@ static int get_device_absolute_path(const unsigned char *device,
 }
 
 /**
- * sysfs_write_device_attr: modify a "writable" attribute for the given device
- * @dev: device bus_id for which attribute has to be changed
- * @attrib: attribute to change
- * @value: value to change to
- * @len: "value" length to write
- * Returns 0 on success -1 on error
- */ 
-int sysfs_write_device_attr(unsigned char *dev, unsigned char *attrib,
-					unsigned char *value, size_t len)
+ * sysfs_open_device: open a device by id (use the "bus" subsystem)
+ * @bus_id: bus_id of the device to open - has to be the "bus_id" in 
+ * 		/sys/bus/xxx/devices
+ * @bus: bus the device belongs to
+ * 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 unsigned char *bus_id, 
+						const unsigned char *bus)
 {
-	struct sysfs_attribute *attribute = NULL;
-	unsigned char devpath[SYSFS_PATH_MAX];
+	char sysfs_path[SYSFS_PATH_MAX];
+	struct sysfs_device *device = NULL;
 
-	if (dev == NULL || attrib == NULL || value == NULL) {
+	if (bus_id == NULL || bus == NULL) {
 		errno = EINVAL;
-		return -1;
+		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;
 	}
 	
-	memset(devpath, 0, SYSFS_PATH_MAX);
-	if ((get_device_absolute_path(dev, devpath, SYSFS_PATH_MAX)) != 0) {
-		dprintf("Error finding absolute path to device %s\n", dev);
-		return -1;
+	device = sysfs_open_device_path(sysfs_path);
+	if (device == NULL) {
+		dprintf("Error opening device %s\n", bus_id);
+		return NULL;
 	}
-	strcat(devpath, "/");
-	strcat(devpath, attrib);
-	attribute = sysfs_open_attribute(devpath);
-	if (attribute == NULL) {
-		dprintf("Attribute %s could not be retrieved for device %s\n",
-				attrib, dev);
-		return -1;
+
+	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)
+{
+	unsigned 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);
+	strcpy(ppath, dev->path);
+	tmp = strrchr(ppath, '/');
+	if (tmp == NULL) {
+		dprintf("Invalid path to device %s\n", ppath);
+		return NULL;
 	}
-	if (attribute->method & SYSFS_METHOD_SHOW) {
-		if ((sysfs_read_attribute(attribute)) != 0) {
-			dprintf("Error reading attribute %s for device %s\n",
-					attrib, dev);
-			sysfs_close_attribute(attribute);
-			return -1;
+	if (*(tmp +1) == '\0') {
+		*tmp = '\0';
+		tmp = strrchr(tmp, '/');
+		if (tmp == NULL) {
+			dprintf("Invalid path to device %s\n", ppath);
+			return NULL;
 		}
 	}
-	if ((sysfs_write_attribute(attribute, value, len)) < 0) {
-		dprintf("Error setting %s to %s\n", attrib, value);
-		sysfs_close_attribute(attribute);
-		return -1;
+	*tmp = '\0';
+	
+	/*
+	 * All "devices" have the "detach_state" attribute - validate here
+	 */
+	strcat(ppath, "/detach_state");
+	if ((sysfs_path_is_file(ppath)) != 0) {
+		dprintf("Device at %s does not have a parent\n", dev->path);
+		return NULL;
 	}
-	sysfs_close_attribute(attribute);
-	return 0;
+	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);
 }
 
-/**
- * sysfs_read_device_attr: read an attribute of the given device
- * @dev: device bus_id for which attribute has to be changed
- * @attrib: attribute to read
- * @value: buffer to return value in
- * @len: size of buffer available
- * Returns 0 on success -1 on error
- */ 
-int sysfs_read_device_attr(unsigned char *dev, unsigned char *attrib,
-					unsigned char *value, size_t len)
+/*
+ * 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 unsigned char *bus,
+		const unsigned char *bus_id, const unsigned char *attrib)
 {
 	struct sysfs_attribute *attribute = NULL;
 	unsigned char devpath[SYSFS_PATH_MAX];
-
-	if (dev == NULL || attrib == NULL || value == NULL) {
+	
+	if (bus == NULL || bus_id == NULL || attrib == NULL) {
 		errno = EINVAL;
-		return -1;
+		return NULL;
 	}
-	
+
 	memset(devpath, 0, SYSFS_PATH_MAX);
-	if ((get_device_absolute_path(dev, devpath, SYSFS_PATH_MAX)) != 0) {
-		dprintf("Error finding absolute path to device %s\n", dev);
-		return -1;
+	if ((get_device_absolute_path(bus_id, bus, devpath, 
+					SYSFS_PATH_MAX)) != 0) {
+		dprintf("Error getting to device %s\n", bus_id);
+		return NULL;
 	}
 	strcat(devpath, "/");
 	strcat(devpath, attrib);
 	attribute = sysfs_open_attribute(devpath);
 	if (attribute == NULL) {
 		dprintf("Error opening attribute %s for device %s\n",
-				attrib, dev);
-		return -1;
-	}
-	if (!(attribute->method & SYSFS_METHOD_SHOW)) {
-		dprintf("Show method not supported for attribute %s\n",
-				attrib);
-		sysfs_close_attribute(attribute);
-		return -1;
+				attrib, bus_id);
+		return NULL;
 	}
 	if ((sysfs_read_attribute(attribute)) != 0) {
 		dprintf("Error reading attribute %s for device %s\n",
-				attrib, dev);
+				attrib, bus_id);
 		sysfs_close_attribute(attribute);
-		return -1;
-	}
-	if (attribute->len > len) {
-		dprintf("Value length %d is larger than supplied buffer %d\n",
-				attribute->len, len);
-		sysfs_close_attribute(attribute);
-		return -1;
+		return NULL;
 	}
-	strncpy(value, attribute->value, attribute->len);
-	value[(attribute->len)+1] = 0;
-	sysfs_close_attribute(attribute);
-	return 0;
+	return attribute;
 }
+