lib/list_sort.c

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