Root/lib/list_sort.c

1#include <linux/kernel.h>
2#include <linux/module.h>
3#include <linux/list_sort.h>
4#include <linux/slab.h>
5#include <linux/list.h>
6
7#define MAX_LIST_LENGTH_BITS 20
8
9/*
10 * Returns a list organized in an intermediate format suited
11 * to chaining of merge() calls: null-terminated, no reserved or
12 * sentinel head node, "prev" links not maintained.
13 */
14static struct list_head *merge(void *priv,
15                int (*cmp)(void *priv, struct list_head *a,
16                    struct list_head *b),
17                struct list_head *a, struct list_head *b)
18{
19    struct list_head head, *tail = &head;
20
21    while (a && b) {
22        /* if equal, take 'a' -- important for sort stability */
23        if ((*cmp)(priv, a, b) <= 0) {
24            tail->next = a;
25            a = a->next;
26        } else {
27            tail->next = b;
28            b = b->next;
29        }
30        tail = tail->next;
31    }
32    tail->next = a?:b;
33    return head.next;
34}
35
36/*
37 * Combine final list merge with restoration of standard doubly-linked
38 * list structure. This approach duplicates code from merge(), but
39 * runs faster than the tidier alternatives of either a separate final
40 * prev-link restoration pass, or maintaining the prev links
41 * throughout.
42 */
43static void merge_and_restore_back_links(void *priv,
44                int (*cmp)(void *priv, struct list_head *a,
45                    struct list_head *b),
46                struct list_head *head,
47                struct list_head *a, struct list_head *b)
48{
49    struct list_head *tail = head;
50
51    while (a && b) {
52        /* if equal, take 'a' -- important for sort stability */
53        if ((*cmp)(priv, a, b) <= 0) {
54            tail->next = a;
55            a->prev = tail;
56            a = a->next;
57        } else {
58            tail->next = b;
59            b->prev = tail;
60            b = b->next;
61        }
62        tail = tail->next;
63    }
64    tail->next = a ? : b;
65
66    do {
67        /*
68         * In worst cases this loop may run many iterations.
69         * Continue callbacks to the client even though no
70         * element comparison is needed, so the client's cmp()
71         * routine can invoke cond_resched() periodically.
72         */
73        (*cmp)(priv, tail->next, tail->next);
74
75        tail->next->prev = tail;
76        tail = tail->next;
77    } while (tail->next);
78
79    tail->next = head;
80    head->prev = tail;
81}
82
83/**
84 * list_sort - sort a list
85 * @priv: private data, opaque to list_sort(), passed to @cmp
86 * @head: the list to sort
87 * @cmp: the elements comparison function
88 *
89 * This function implements "merge sort", which has O(nlog(n))
90 * complexity.
91 *
92 * The comparison function @cmp must return a negative value if @a
93 * should sort before @b, and a positive value if @a should sort after
94 * @b. If @a and @b are equivalent, and their original relative
95 * ordering is to be preserved, @cmp must return 0.
96 */
97void list_sort(void *priv, struct list_head *head,
98        int (*cmp)(void *priv, struct list_head *a,
99            struct list_head *b))
100{
101    struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
102                        -- last slot is a sentinel */
103    int lev; /* index into part[] */
104    int max_lev = 0;
105    struct list_head *list;
106
107    if (list_empty(head))
108        return;
109
110    memset(part, 0, sizeof(part));
111
112    head->prev->next = NULL;
113    list = head->next;
114
115    while (list) {
116        struct list_head *cur = list;
117        list = list->next;
118        cur->next = NULL;
119
120        for (lev = 0; part[lev]; lev++) {
121            cur = merge(priv, cmp, part[lev], cur);
122            part[lev] = NULL;
123        }
124        if (lev > max_lev) {
125            if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
126                printk_once(KERN_DEBUG "list passed to"
127                    " list_sort() too long for"
128                    " efficiency\n");
129                lev--;
130            }
131            max_lev = lev;
132        }
133        part[lev] = cur;
134    }
135
136    for (lev = 0; lev < max_lev; lev++)
137        if (part[lev])
138            list = merge(priv, cmp, part[lev], list);
139
140    merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
141}
142EXPORT_SYMBOL(list_sort);
143
144#ifdef CONFIG_TEST_LIST_SORT
145
146#include <linux/random.h>
147
148/*
149 * The pattern of set bits in the list length determines which cases
150 * are hit in list_sort().
151 */
152#define TEST_LIST_LEN (512+128+2) /* not including head */
153
154#define TEST_POISON1 0xDEADBEEF
155#define TEST_POISON2 0xA324354C
156
157struct debug_el {
158    unsigned int poison1;
159    struct list_head list;
160    unsigned int poison2;
161    int value;
162    unsigned serial;
163};
164
165/* Array, containing pointers to all elements in the test list */
166static struct debug_el **elts __initdata;
167
168static int __init check(struct debug_el *ela, struct debug_el *elb)
169{
170    if (ela->serial >= TEST_LIST_LEN) {
171        printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
172                ela->serial);
173        return -EINVAL;
174    }
175    if (elb->serial >= TEST_LIST_LEN) {
176        printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
177                elb->serial);
178        return -EINVAL;
179    }
180    if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
181        printk(KERN_ERR "list_sort_test: error: phantom element\n");
182        return -EINVAL;
183    }
184    if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
185        printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
186                ela->poison1, ela->poison2);
187        return -EINVAL;
188    }
189    if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
190        printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
191                elb->poison1, elb->poison2);
192        return -EINVAL;
193    }
194    return 0;
195}
196
197static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
198{
199    struct debug_el *ela, *elb;
200
201    ela = container_of(a, struct debug_el, list);
202    elb = container_of(b, struct debug_el, list);
203
204    check(ela, elb);
205    return ela->value - elb->value;
206}
207
208static int __init list_sort_test(void)
209{
210    int i, count = 1, err = -EINVAL;
211    struct debug_el *el;
212    struct list_head *cur, *tmp;
213    LIST_HEAD(head);
214
215    printk(KERN_DEBUG "list_sort_test: start testing list_sort()\n");
216
217    elts = kmalloc(sizeof(void *) * TEST_LIST_LEN, GFP_KERNEL);
218    if (!elts) {
219        printk(KERN_ERR "list_sort_test: error: cannot allocate "
220                "memory\n");
221        goto exit;
222    }
223
224    for (i = 0; i < TEST_LIST_LEN; i++) {
225        el = kmalloc(sizeof(*el), GFP_KERNEL);
226        if (!el) {
227            printk(KERN_ERR "list_sort_test: error: cannot "
228                    "allocate memory\n");
229            goto exit;
230        }
231         /* force some equivalencies */
232        el->value = prandom_u32() % (TEST_LIST_LEN / 3);
233        el->serial = i;
234        el->poison1 = TEST_POISON1;
235        el->poison2 = TEST_POISON2;
236        elts[i] = el;
237        list_add_tail(&el->list, &head);
238    }
239
240    list_sort(NULL, &head, cmp);
241
242    for (cur = head.next; cur->next != &head; cur = cur->next) {
243        struct debug_el *el1;
244        int cmp_result;
245
246        if (cur->next->prev != cur) {
247            printk(KERN_ERR "list_sort_test: error: list is "
248                    "corrupted\n");
249            goto exit;
250        }
251
252        cmp_result = cmp(NULL, cur, cur->next);
253        if (cmp_result > 0) {
254            printk(KERN_ERR "list_sort_test: error: list is not "
255                    "sorted\n");
256            goto exit;
257        }
258
259        el = container_of(cur, struct debug_el, list);
260        el1 = container_of(cur->next, struct debug_el, list);
261        if (cmp_result == 0 && el->serial >= el1->serial) {
262            printk(KERN_ERR "list_sort_test: error: order of "
263                    "equivalent elements not preserved\n");
264            goto exit;
265        }
266
267        if (check(el, el1)) {
268            printk(KERN_ERR "list_sort_test: error: element check "
269                    "failed\n");
270            goto exit;
271        }
272        count++;
273    }
274
275    if (count != TEST_LIST_LEN) {
276        printk(KERN_ERR "list_sort_test: error: bad list length %d",
277                count);
278        goto exit;
279    }
280
281    err = 0;
282exit:
283    kfree(elts);
284    list_for_each_safe(cur, tmp, &head) {
285        list_del(cur);
286        kfree(container_of(cur, struct debug_el, list));
287    }
288    return err;
289}
290module_init(list_sort_test);
291#endif /* CONFIG_TEST_LIST_SORT */
292

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