source: mainline/uspace/lib/ext4/src/bitmap.c@ 8d2dd7f2

/*
 * Copyright (c) 2012 Frantisek Princ
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup libext4
 * @{
 */
/**
 * @file  bitmap.c
 * @brief Ext4 bitmap operations.
 */

#include <errno.h>
#include <block.h>
#include <stdint.h>
#include "ext4/bitmap.h"

/** Set bit in bitmap to 0 (free).
 *
 * Index must be checked by caller, if it's not out of bounds.
 *
 * @param bitmap Pointer to bitmap
 * @param index  Index of bit in bitmap
 *
 */
void ext4_bitmap_free_bit(uint8_t *bitmap, uint32_t index)
{
        uint32_t byte_index = index / 8;
        uint32_t bit_index = index % 8;
        
        uint8_t *target = bitmap + byte_index;
        
        *target &= ~ (1 << bit_index);
}

/** Free continous set of bits (set to 0).
 *
 * Index and count must be checked by caller, if they aren't out of bounds.
 *
 * @param bitmap Pointer to bitmap
 * @param index  Index of first bit to zeroed
 * @param count  Number of bits to be zeroed
 *
 */
void ext4_bitmap_free_bits(uint8_t *bitmap, uint32_t index, uint32_t count)
{
        uint8_t *target;
        uint32_t idx = index;
        uint32_t remaining = count;
        uint32_t byte_index;
        
        /* Align index to multiple of 8 */
        while (((idx % 8) != 0) && (remaining > 0)) {
                byte_index = idx / 8;
                uint32_t bit_index = idx % 8;
                
                target = bitmap + byte_index;
                *target &= ~ (1 << bit_index);
                
                idx++;
                remaining--;
        }
        
        /* For < 8 bits this check necessary */
        if (remaining == 0)
                return;
        
        assert((idx % 8) == 0);
        
        byte_index = idx / 8;
        target = bitmap + byte_index;
        
        /* Zero the whole bytes */
        while (remaining >= 8) {
                *target = 0;
                
                idx += 8;
                remaining -= 8;
                target++;
        }
        
        assert(remaining < 8);
        
        /* Zero remaining bytes */
        while (remaining != 0) {
                byte_index = idx / 8;
                uint32_t bit_index = idx % 8;
                
                target = bitmap + byte_index;
                *target &= ~ (1 << bit_index);
                
                idx++;
                remaining--;
        }
}

/** Set bit in bitmap to 1 (used).
 *
 * @param bitmap Pointer to bitmap
 * @param index  Index of bit to set
 *
 */
void ext4_bitmap_set_bit(uint8_t *bitmap, uint32_t index)
{
        uint32_t byte_index = index / 8;
        uint32_t bit_index = index % 8;
        
        uint8_t *target = bitmap + byte_index;
        
        *target |= 1 << bit_index;
}

/** Check if requested bit is free.
 *
 * @param bitmap Pointer to bitmap
 * @param index  Index of bit to be checked
 *
 * @return True if bit is free, else false
 *
 */
bool ext4_bitmap_is_free_bit(uint8_t *bitmap, uint32_t index)
{
        uint32_t byte_index = index / 8;
        uint32_t bit_index = index % 8;
        
        uint8_t *target = bitmap + byte_index;
        
        if (*target & (1 << bit_index))
                return false;
        else
                return true;
}

/** Try to find free byte and set the first bit as used.
 *
 * Walk through bitmap and try to find free byte (equal to 0).
 * If byte found, set the first bit as used.
 *
 * @param bitmap Pointer to bitmap
 * @param start  Index of bit, where the algorithm will begin
 * @param index  Output value - index of bit (if found free byte)
 * @param max    Maximum index of bit in bitmap
 *
 * @return Error code
 *
 */
int ext4_bitmap_find_free_byte_and_set_bit(uint8_t *bitmap, uint32_t start,
    uint32_t *index, uint32_t max)
{
        uint32_t idx;
        
        /* Align idx */
        if (start % 8)
                idx = start + (8 - (start % 8));
        else
                idx = start;
        
        uint8_t *pos = bitmap + (idx / 8);
        
        /* Try to find free byte */
        while (idx < max) {
                if (*pos == 0) {
                        *pos |= 1;
                        
                        *index = idx;
                        return EOK;
                }
                
                idx += 8;
                ++pos;
        }
        
        /* Free byte not found */
        return ENOSPC;
}

/** Try to find free bit and set it as used (1).
 *
 * Walk through bitmap and try to find any free bit.
 *
 * @param bitmap    Pointer to bitmap
 * @param start_idx Index of bit, where algorithm will begin
 * @param index     Output value - index of set bit (if found)
 * @param max       Maximum index of bit in bitmap
 *
 * @return Error code
 *
 */
int ext4_bitmap_find_free_bit_and_set(uint8_t *bitmap, uint32_t start_idx,
    uint32_t *index, uint32_t max)
{
        uint8_t *pos = bitmap + (start_idx / 8);
        uint32_t idx = start_idx;
        bool byte_part = false;
        
        /* Check the rest of first byte */
        while ((idx % 8) != 0) {
                byte_part = true;
                
                if ((*pos & (1 << (idx % 8))) == 0) {
                        *pos |= (1 << (idx % 8));
                        *index = idx;
                        return EOK;
                }
                
                ++idx;
        }
        
        if (byte_part)
                ++pos;
        
        /* Check the whole bytes (255 = 11111111 binary) */
        while (idx < max) {
                if ((*pos & 255) != 255) {
                        /* Free bit found */
                        break;
                }
                
                idx += 8;
                ++pos;
        }
        
        /* If idx < max, some free bit found */
        if (idx < max) {
                /* Check which bit from byte is free */
                for (uint8_t i = 0; i < 8; ++i) {
                        if ((*pos & (1 << i)) == 0) {
                                /* Free bit found */
                                *pos |= (1 << i);
                                
                                *index = idx;
                                return EOK;
                        }
                        
                        idx++;
                }
        }
        
        /* Free bit not found */
        return ENOSPC;
}

/**
 * @}
 */