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Linux/lib/list_sort.c

  1 
  2 #define pr_fmt(fmt) "list_sort_test: " fmt
  3 
  4 #include <linux/kernel.h>
  5 #include <linux/bug.h>
  6 #include <linux/compiler.h>
  7 #include <linux/export.h>
  8 #include <linux/string.h>
  9 #include <linux/list_sort.h>
 10 #include <linux/list.h>
 11 
 12 #define MAX_LIST_LENGTH_BITS 20
 13 
 14 /*
 15  * Returns a list organized in an intermediate format suited
 16  * to chaining of merge() calls: null-terminated, no reserved or
 17  * sentinel head node, "prev" links not maintained.
 18  */
 19 static struct list_head *merge(void *priv,
 20                                 int (*cmp)(void *priv, struct list_head *a,
 21                                         struct list_head *b),
 22                                 struct list_head *a, struct list_head *b)
 23 {
 24         struct list_head head, *tail = &head;
 25 
 26         while (a && b) {
 27                 /* if equal, take 'a' -- important for sort stability */
 28                 if ((*cmp)(priv, a, b) <= 0) {
 29                         tail->next = a;
 30                         a = a->next;
 31                 } else {
 32                         tail->next = b;
 33                         b = b->next;
 34                 }
 35                 tail = tail->next;
 36         }
 37         tail->next = a?:b;
 38         return head.next;
 39 }
 40 
 41 /*
 42  * Combine final list merge with restoration of standard doubly-linked
 43  * list structure.  This approach duplicates code from merge(), but
 44  * runs faster than the tidier alternatives of either a separate final
 45  * prev-link restoration pass, or maintaining the prev links
 46  * throughout.
 47  */
 48 static void merge_and_restore_back_links(void *priv,
 49                                 int (*cmp)(void *priv, struct list_head *a,
 50                                         struct list_head *b),
 51                                 struct list_head *head,
 52                                 struct list_head *a, struct list_head *b)
 53 {
 54         struct list_head *tail = head;
 55         u8 count = 0;
 56 
 57         while (a && b) {
 58                 /* if equal, take 'a' -- important for sort stability */
 59                 if ((*cmp)(priv, a, b) <= 0) {
 60                         tail->next = a;
 61                         a->prev = tail;
 62                         a = a->next;
 63                 } else {
 64                         tail->next = b;
 65                         b->prev = tail;
 66                         b = b->next;
 67                 }
 68                 tail = tail->next;
 69         }
 70         tail->next = a ? : b;
 71 
 72         do {
 73                 /*
 74                  * In worst cases this loop may run many iterations.
 75                  * Continue callbacks to the client even though no
 76                  * element comparison is needed, so the client's cmp()
 77                  * routine can invoke cond_resched() periodically.
 78                  */
 79                 if (unlikely(!(++count)))
 80                         (*cmp)(priv, tail->next, tail->next);
 81 
 82                 tail->next->prev = tail;
 83                 tail = tail->next;
 84         } while (tail->next);
 85 
 86         tail->next = head;
 87         head->prev = tail;
 88 }
 89 
 90 /**
 91  * list_sort - sort a list
 92  * @priv: private data, opaque to list_sort(), passed to @cmp
 93  * @head: the list to sort
 94  * @cmp: the elements comparison function
 95  *
 96  * This function implements "merge sort", which has O(nlog(n))
 97  * complexity.
 98  *
 99  * The comparison function @cmp must return a negative value if @a
100  * should sort before @b, and a positive value if @a should sort after
101  * @b. If @a and @b are equivalent, and their original relative
102  * ordering is to be preserved, @cmp must return 0.
103  */
104 void list_sort(void *priv, struct list_head *head,
105                 int (*cmp)(void *priv, struct list_head *a,
106                         struct list_head *b))
107 {
108         struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
109                                                 -- last slot is a sentinel */
110         int lev;  /* index into part[] */
111         int max_lev = 0;
112         struct list_head *list;
113 
114         if (list_empty(head))
115                 return;
116 
117         memset(part, 0, sizeof(part));
118 
119         head->prev->next = NULL;
120         list = head->next;
121 
122         while (list) {
123                 struct list_head *cur = list;
124                 list = list->next;
125                 cur->next = NULL;
126 
127                 for (lev = 0; part[lev]; lev++) {
128                         cur = merge(priv, cmp, part[lev], cur);
129                         part[lev] = NULL;
130                 }
131                 if (lev > max_lev) {
132                         if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
133                                 printk_once(KERN_DEBUG "list too long for efficiency\n");
134                                 lev--;
135                         }
136                         max_lev = lev;
137                 }
138                 part[lev] = cur;
139         }
140 
141         for (lev = 0; lev < max_lev; lev++)
142                 if (part[lev])
143                         list = merge(priv, cmp, part[lev], list);
144 
145         merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
146 }
147 EXPORT_SYMBOL(list_sort);
148 
149 #ifdef CONFIG_TEST_LIST_SORT
150 
151 #include <linux/slab.h>
152 #include <linux/random.h>
153 
154 /*
155  * The pattern of set bits in the list length determines which cases
156  * are hit in list_sort().
157  */
158 #define TEST_LIST_LEN (512+128+2) /* not including head */
159 
160 #define TEST_POISON1 0xDEADBEEF
161 #define TEST_POISON2 0xA324354C
162 
163 struct debug_el {
164         unsigned int poison1;
165         struct list_head list;
166         unsigned int poison2;
167         int value;
168         unsigned serial;
169 };
170 
171 /* Array, containing pointers to all elements in the test list */
172 static struct debug_el **elts __initdata;
173 
174 static int __init check(struct debug_el *ela, struct debug_el *elb)
175 {
176         if (ela->serial >= TEST_LIST_LEN) {
177                 pr_err("error: incorrect serial %d\n", ela->serial);
178                 return -EINVAL;
179         }
180         if (elb->serial >= TEST_LIST_LEN) {
181                 pr_err("error: incorrect serial %d\n", elb->serial);
182                 return -EINVAL;
183         }
184         if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
185                 pr_err("error: phantom element\n");
186                 return -EINVAL;
187         }
188         if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
189                 pr_err("error: bad poison: %#x/%#x\n",
190                         ela->poison1, ela->poison2);
191                 return -EINVAL;
192         }
193         if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
194                 pr_err("error: bad poison: %#x/%#x\n",
195                         elb->poison1, elb->poison2);
196                 return -EINVAL;
197         }
198         return 0;
199 }
200 
201 static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
202 {
203         struct debug_el *ela, *elb;
204 
205         ela = container_of(a, struct debug_el, list);
206         elb = container_of(b, struct debug_el, list);
207 
208         check(ela, elb);
209         return ela->value - elb->value;
210 }
211 
212 static int __init list_sort_test(void)
213 {
214         int i, count = 1, err = -ENOMEM;
215         struct debug_el *el;
216         struct list_head *cur;
217         LIST_HEAD(head);
218 
219         pr_debug("start testing list_sort()\n");
220 
221         elts = kcalloc(TEST_LIST_LEN, sizeof(*elts), GFP_KERNEL);
222         if (!elts) {
223                 pr_err("error: cannot allocate memory\n");
224                 return err;
225         }
226 
227         for (i = 0; i < TEST_LIST_LEN; i++) {
228                 el = kmalloc(sizeof(*el), GFP_KERNEL);
229                 if (!el) {
230                         pr_err("error: cannot allocate memory\n");
231                         goto exit;
232                 }
233                  /* force some equivalencies */
234                 el->value = prandom_u32() % (TEST_LIST_LEN / 3);
235                 el->serial = i;
236                 el->poison1 = TEST_POISON1;
237                 el->poison2 = TEST_POISON2;
238                 elts[i] = el;
239                 list_add_tail(&el->list, &head);
240         }
241 
242         list_sort(NULL, &head, cmp);
243 
244         err = -EINVAL;
245         for (cur = head.next; cur->next != &head; cur = cur->next) {
246                 struct debug_el *el1;
247                 int cmp_result;
248 
249                 if (cur->next->prev != cur) {
250                         pr_err("error: list is corrupted\n");
251                         goto exit;
252                 }
253 
254                 cmp_result = cmp(NULL, cur, cur->next);
255                 if (cmp_result > 0) {
256                         pr_err("error: list is not sorted\n");
257                         goto exit;
258                 }
259 
260                 el = container_of(cur, struct debug_el, list);
261                 el1 = container_of(cur->next, struct debug_el, list);
262                 if (cmp_result == 0 && el->serial >= el1->serial) {
263                         pr_err("error: order of equivalent elements not "
264                                 "preserved\n");
265                         goto exit;
266                 }
267 
268                 if (check(el, el1)) {
269                         pr_err("error: element check failed\n");
270                         goto exit;
271                 }
272                 count++;
273         }
274         if (head.prev != cur) {
275                 pr_err("error: list is corrupted\n");
276                 goto exit;
277         }
278 
279 
280         if (count != TEST_LIST_LEN) {
281                 pr_err("error: bad list length %d", count);
282                 goto exit;
283         }
284 
285         err = 0;
286 exit:
287         for (i = 0; i < TEST_LIST_LEN; i++)
288                 kfree(elts[i]);
289         kfree(elts);
290         return err;
291 }
292 late_initcall(list_sort_test);
293 #endif /* CONFIG_TEST_LIST_SORT */
294 

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