/*

 * Copyright (C) 2005-2006 Kay Sievers <kay.sievers@vrfy.org>

 *	              2008 Jaroslav Kysela <perex@perex.cz>

 *

 *	This program is free software; you can redistribute it and/or modify it

 *	under the terms of the GNU General Public License as published by the

 *	Free Software Foundation version 2 of the License.

 * 

 *	This program is distributed in the hope that it will be useful, but

 *	WITHOUT ANY WARRANTY; without even the implied warranty of

 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 *	General Public License for more details.

 * 

 *	You should have received a copy of the GNU General Public License along

 *	with this program; if not, write to the Free Software Foundation, Inc.,

 *	51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

 *

 */

static char sysfs_path[PATH_SIZE];

/* attribute value cache */

static LIST_HEAD(attr_list);

struct sysfs_attr {

	struct list_head node;

	char path[PATH_SIZE];

	char *value;			/* points to value_local if value is cached */

	char value_local[NAME_SIZE];

};

static int sysfs_init(void)

{

	const char *env;

	char sysfs_test[PATH_SIZE];

	INIT_LIST_HEAD(&attr_list);

	env = getenv("SYSFS_PATH");

	if (env) {

		strlcpy(sysfs_path, env, sizeof(sysfs_path));

		remove_trailing_chars(sysfs_path, '/');

	} else

		strlcpy(sysfs_path, "/sys", sizeof(sysfs_path));

	dbg("sysfs_path='%s'", sysfs_path);

	strlcpy(sysfs_test, sysfs_path, sizeof(sysfs_test));

	strlcat(sysfs_test, "/kernel/uevent_seqnum", sizeof(sysfs_test));

	if (access(sysfs_test, F_OK)) {

		strlcpy(sysfs_test, sysfs_path, sizeof(sysfs_test));

		strlcat(sysfs_test, "/kernel/uevent_helper", sizeof(sysfs_test));

		if (access(sysfs_test, F_OK)) {

			error("sysfs path '%s' is invalid", sysfs_path);

			return -errno;

		}

	}

	return 0;

}

static void sysfs_cleanup(void)

{

	struct sysfs_attr *attr_loop;

	struct sysfs_attr *attr_temp;

	list_for_each_entry_safe(attr_loop, attr_temp, &attr_list, node) {

		list_del(&attr_loop->node);

		free(attr_loop);

	}

}

static char *sysfs_attr_get_value(const char *devpath, const char *attr_name)

{

	char path_full[PATH_SIZE];

	const char *path;

	char value[NAME_SIZE];

	struct sysfs_attr *attr_loop;

	struct sysfs_attr *attr;

	struct stat statbuf;

	int fd;

	ssize_t size;

	size_t sysfs_len;

	dbg("open '%s'/'%s'", devpath, attr_name);

	sysfs_len = strlcpy(path_full, sysfs_path, sizeof(path_full));

	path = &path_full[sysfs_len];

	strlcat(path_full, devpath, sizeof(path_full));

	strlcat(path_full, "/", sizeof(path_full));

	strlcat(path_full, attr_name, sizeof(path_full));

	/* look for attribute in cache */

	list_for_each_entry(attr_loop, &attr_list, node) {

		if (strcmp(attr_loop->path, path) == 0) {

			dbg("found in cache '%s'", attr_loop->path);

			return attr_loop->value;

		}

	}

	/* store attribute in cache (also negatives are kept in cache) */

	dbg("new uncached attribute '%s'", path_full);

	attr = malloc(sizeof(struct sysfs_attr));

	if (attr == NULL)

		return NULL;

	memset(attr, 0x00, sizeof(struct sysfs_attr));

	strlcpy(attr->path, path, sizeof(attr->path));

	dbg("add to cache '%s'", path_full);

	list_add(&attr->node, &attr_list);

	if (lstat(path_full, &statbuf) != 0) {

		dbg("stat '%s' failed: %s", path_full, strerror(errno));

		goto out;

	}

	if (S_ISLNK(statbuf.st_mode)) {

		/* links return the last element of the target path */

		char link_target[PATH_SIZE + 1];

		int len;

		const char *pos;

		len = readlink(path_full, link_target, sizeof(link_target) - 1);

		if (len > 0) {

			link_target[len] = '\0';

			pos = strrchr(link_target, '/');

			if (pos != NULL) {

				dbg("cache '%s' with link value '%s'", path_full, pos+1);

				strlcpy(attr->value_local, &pos[1], sizeof(attr->value_local));

				attr->value = attr->value_local;

			}

		}

		goto out;

	}

	/* skip directories */

	if (S_ISDIR(statbuf.st_mode))

		goto out;

	/* skip non-readable files */

	if ((statbuf.st_mode & S_IRUSR) == 0)

		goto out;

	/* read attribute value */

	fd = open(path_full, O_RDONLY);

	if (fd < 0) {

		dbg("attribute '%s' does not exist", path_full);

		goto out;

	}

	size = read(fd, value, sizeof(value));

	close(fd);

	if (size < 0)

		goto out;

	if (size == sizeof(value))

		goto out;

	/* got a valid value, store and return it */

	value[size] = '\0';

	remove_trailing_chars(value, '\n');

	dbg("cache '%s' with attribute value '%s'", path_full, value);

	strlcpy(attr->value_local, value, sizeof(attr->value_local));

	attr->value = attr->value_local;

out:

	return attr->value;

}