libudev: list - use binary search for list lookup

[thirdparty/systemd.git] / libudev / libudev-list.c

/*
 * libudev - interface to udev device information
 *
 * Copyright (C) 2008 Kay Sievers <kay.sievers@vrfy.org>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 */

#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#include "libudev.h"
#include "libudev-private.h"

/**
 * SECTION:libudev-list
 * @short_description: list operation
 *
 * Libudev list operations.
 */

/**
 * udev_list_entry:
 *
 * Opaque object representing one entry in a list. An entry contains
 * contains a name, and optionally a value.
 */
struct udev_list_entry {
	struct udev_list_node node;
	struct udev_list *list;
	char *name;
	char *value;
	int num;
};

/* the list's head points to itself if empty */
void udev_list_node_init(struct udev_list_node *list)
{
	list->next = list;
	list->prev = list;
}

int udev_list_node_is_empty(struct udev_list_node *list)
{
	return list->next == list;
}

static void udev_list_node_insert_between(struct udev_list_node *new,
					  struct udev_list_node *prev,
					  struct udev_list_node *next)
{
	next->prev = new;
	new->next = next;
	new->prev = prev;
	prev->next = new;
}

void udev_list_node_append(struct udev_list_node *new, struct udev_list_node *list)
{
	udev_list_node_insert_between(new, list->prev, list);
}

void udev_list_node_remove(struct udev_list_node *entry)
{
	struct udev_list_node *prev = entry->prev;
	struct udev_list_node *next = entry->next;

	next->prev = prev;
	prev->next = next;

	entry->prev = NULL;
	entry->next = NULL;
}

/* return list entry which embeds this node */
static struct udev_list_entry *list_node_to_entry(struct udev_list_node *node)
{
	char *list;

	list = (char *)node;
	list -= offsetof(struct udev_list_entry, node);
	return (struct udev_list_entry *)list;
}

void udev_list_init(struct udev *udev, struct udev_list *list, bool unique)
{
	memset(list, 0x00, sizeof(struct udev_list));
	list->udev = udev;
	list->unique = unique;
	udev_list_node_init(&list->node);
}

/* insert entry into a list as the last element  */
void udev_list_entry_append(struct udev_list_entry *new, struct udev_list *list)
{
	/* inserting before the list head make the node the last node in the list */
	udev_list_node_insert_between(&new->node, list->node.prev, &list->node);
	new->list = list;
}

/* insert entry into a list, before a given existing entry */
void udev_list_entry_insert_before(struct udev_list_entry *new, struct udev_list_entry *entry)
{
	udev_list_node_insert_between(&new->node, entry->node.prev, &entry->node);
	new->list = entry->list;
}

/* binary search in sorted array */
static int list_search(struct udev_list *list, const char *name)
{
	unsigned int first, last;

	first = 0;
	last = list->entries_cur;
	while (first < last) {
		unsigned int i;
		int cmp;

		i = (first + last)/2;
		cmp = strcmp(name, list->entries[i]->name);
		if (cmp < 0)
			last = i;
		else if (cmp > 0)
			first = i+1;
		else
			return i;
	}

	/* not found, return negative insertion-index+1 */
	return -(first+1);
}

struct udev_list_entry *udev_list_entry_add(struct udev_list *list, const char *name, const char *value)
{
	struct udev_list_entry *entry;
	int i = 0;

	if (list->unique) {
		/* lookup existing name or insertion-index */
		i = list_search(list, name);
		if (i >= 0) {
			entry = list->entries[i];

			dbg(list->udev, "'%s' is already in the list\n", name);
			free(entry->value);
			if (value == NULL) {
				entry->value = NULL;
				dbg(list->udev, "'%s' value unset\n", name);
				return entry;
			}
			entry->value = strdup(value);
			if (entry->value == NULL)
				return NULL;
			dbg(list->udev, "'%s' value replaced with '%s'\n", name, value);
			return entry;
		}
	}

	/* add new name */
	entry = calloc(1, sizeof(struct udev_list_entry));
	if (entry == NULL)
		return NULL;
	entry->name = strdup(name);
	if (entry->name == NULL) {
		free(entry);
		return NULL;
	}
	if (value != NULL) {
		entry->value = strdup(value);
		if (entry->value == NULL) {
			free(entry->name);
			free(entry);
			return NULL;
		}
	}
	udev_list_entry_append(entry, list);

	if (list->unique) {
		/* allocate or enlarge sorted array if needed */
		if (list->entries_cur >= list->entries_max) {
			unsigned int add;

			add = list->entries_max;
			if (add < 1)
				add = 64;
			list->entries = realloc(list->entries, (list->entries_max + add) * sizeof(struct udev_list_entry *));
			if (list->entries == NULL) {
				free(entry->name);
				free(entry->value);
				return NULL;
			}
			list->entries_max += add;
		}

		/* insert into sorted array */
		i = (-i)-1;
		memmove(&list->entries[i+1], &list->entries[i],
		        (list->entries_cur - i) * sizeof(struct udev_list_entry *));
		list->entries[i] = entry;
		list->entries_cur++;
	}

	dbg(list->udev, "'%s=%s' added\n", entry->name, entry->value);
	return entry;
}

void udev_list_entry_delete(struct udev_list_entry *entry)
{
	if (entry->list->entries != NULL) {
		int i;
		struct udev_list *list = entry->list;

		/* remove entry from sorted array */
		i = list_search(list, entry->name);
		if (i >= 0) {
			memmove(&list->entries[i], &list->entries[i+1],
			        ((list->entries_cur-1) - i) * sizeof(struct udev_list_entry *));
			list->entries_cur--;
		}
	}

	udev_list_node_remove(&entry->node);
	free(entry->name);
	free(entry->value);
	free(entry);
}

void udev_list_cleanup(struct udev_list *list)
{
	struct udev_list_entry *entry_loop;
	struct udev_list_entry *entry_tmp;

	free(list->entries);
	list->entries = NULL;
	list->entries_cur = 0;
	list->entries_max = 0;
	udev_list_entry_foreach_safe(entry_loop, entry_tmp, udev_list_get_entry(list))
		udev_list_entry_delete(entry_loop);
}

struct udev_list_entry *udev_list_get_entry(struct udev_list *list)
{
	if (udev_list_node_is_empty(&list->node))
		return NULL;
	return list_node_to_entry(list->node.next);
}

/**
 * udev_list_entry_get_next:
 * @list_entry: current entry
 *
 * Returns: the next entry from the list, #NULL is no more entries are found.
 */
UDEV_EXPORT struct udev_list_entry *udev_list_entry_get_next(struct udev_list_entry *list_entry)
{
	struct udev_list_node *next;

	if (list_entry == NULL)
		return NULL;
	next = list_entry->node.next;
	/* empty list or no more entries */
	if (next == &list_entry->list->node)
		return NULL;
	return list_node_to_entry(next);
}

/**
 * udev_list_entry_get_by_name:
 * @list_entry: current entry
 * @name: name string to match
 *
 * Returns: the entry where @name matched, #NULL if no matching entry is found.
 */
UDEV_EXPORT struct udev_list_entry *udev_list_entry_get_by_name(struct udev_list_entry *list_entry, const char *name)
{
	int i;

	if (list_entry == NULL)
		return NULL;

	if (!list_entry->list->unique)
		return NULL;

	i = list_search(list_entry->list, name);
	if (i < 0)
		return NULL;
	return list_entry->list->entries[i];
}

/**
 * udev_list_entry_get_name:
 * @list_entry: current entry
 *
 * Returns: the name string of this entry.
 */
UDEV_EXPORT const char *udev_list_entry_get_name(struct udev_list_entry *list_entry)
{
	if (list_entry == NULL)
		return NULL;
	return list_entry->name;
}

/**
 * udev_list_entry_get_value:
 * @list_entry: current entry
 *
 * Returns: the value string of this entry.
 */
UDEV_EXPORT const char *udev_list_entry_get_value(struct udev_list_entry *list_entry)
{
	if (list_entry == NULL)
		return NULL;
	return list_entry->value;
}

int udev_list_entry_get_num(struct udev_list_entry *list_entry)
{
	if (list_entry == NULL)
		return -EINVAL;
	return list_entry->num;
}

void udev_list_entry_set_num(struct udev_list_entry *list_entry, int num)
{
	if (list_entry == NULL)
		return;
	list_entry->num = num;
}