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 */