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bitext.c

/*
 * bitext.c: kernel little helper (of bit shuffling variety).
 *
 * Copyright (C) 2002 Pete Zaitcev <zaitcev@yahoo.com>
 *
 * The algorithm to search a zero bit string is geared towards its application.
 * We expect a couple of fixed sizes of requests, so a rotating counter, reset
 * by align size, should provide fast enough search while maintaining low
 * fragmentation.
 */

#include <linux/string.h>
#include <linux/bitops.h>

#include <asm/bitext.h>

/**
 * bit_map_string_get - find and set a bit string in bit map.
 * @t: the bit map.
 * @len: requested string length
 * @align: requested alignment
 *
 * Returns offset in the map or -1 if out of space.
 *
 * Not safe to call from an interrupt (uses spin_lock).
 */
int bit_map_string_get(struct bit_map *t, int len, int align)
{
      int offset, count;      /* siamese twins */
      int off_new;
      int align1;
      int i, color;

      if (t->num_colors) {
            /* align is overloaded to be the page color */
            color = align;
            align = t->num_colors;
      } else {
            color = 0;
            if (align == 0)
                  align = 1;
      }
      align1 = align - 1;
      if ((align & align1) != 0)
            BUG();
      if (align < 0 || align >= t->size)
            BUG();
      if (len <= 0 || len > t->size)
            BUG();
      color &= align1;

      spin_lock(&t->lock);
      if (len < t->last_size)
            offset = t->first_free;
      else
            offset = t->last_off & ~align1;
      count = 0;
      for (;;) {
            off_new = find_next_zero_bit(t->map, t->size, offset);
            off_new = ((off_new + align1) & ~align1) + color;
            count += off_new - offset;
            offset = off_new;
            if (offset >= t->size)
                  offset = 0;
            if (count + len > t->size) {
                  spin_unlock(&t->lock);
/* P3 */ printk(KERN_ERR
  "bitmap out: size %d used %d off %d len %d align %d count %d\n",
  t->size, t->used, offset, len, align, count);
                  return -1;
            }

            if (offset + len > t->size) {
                  count += t->size - offset;
                  offset = 0;
                  continue;
            }

            i = 0;
            while (test_bit(offset + i, t->map) == 0) {
                  i++;
                  if (i == len) {
                        for (i = 0; i < len; i++)
                              __set_bit(offset + i, t->map);
                        if (offset == t->first_free)
                              t->first_free = find_next_zero_bit
                                          (t->map, t->size,
                                           t->first_free + len);
                        if ((t->last_off = offset + len) >= t->size)
                              t->last_off = 0;
                        t->used += len;
                        t->last_size = len;
                        spin_unlock(&t->lock);
                        return offset;
                  }
            }
            count += i + 1;
            if ((offset += i + 1) >= t->size)
                  offset = 0;
      }
}

void bit_map_clear(struct bit_map *t, int offset, int len)
{
      int i;

      if (t->used < len)
            BUG();            /* Much too late to do any good, but alas... */
      spin_lock(&t->lock);
      for (i = 0; i < len; i++) {
            if (test_bit(offset + i, t->map) == 0)
                  BUG();
            __clear_bit(offset + i, t->map);
      }
      if (offset < t->first_free)
            t->first_free = offset;
      t->used -= len;
      spin_unlock(&t->lock);
}

void bit_map_init(struct bit_map *t, unsigned long *map, int size)
{

      if ((size & 07) != 0)
            BUG();
      memset(map, 0, size>>3);

      memset(t, 0, sizeof *t);
      spin_lock_init(&t->lock);
      t->map = map;
      t->size = size;
}

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