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  */
  14 static 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  */
  43 static 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  */
  97 void 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 }
 142 EXPORT_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
 157 struct 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 */
 166 static struct debug_el **elts __initdata;
 167
 168 static 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
 197 static 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
 208 static 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;
 282 exit:
 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 }
 290 module_init(list_sort_test);
 291 #endif /* CONFIG_TEST_LIST_SORT */