bitext.c
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/*
* 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/bitmap.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) {
bitmap_set(t->map, offset, len);
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)
{
bitmap_zero(map, size);
memset(t, 0, sizeof *t);
spin_lock_init(&t->lock);
t->map = map;
t->size = size;
}