source: mainline/uspace/lib/mbr/libmbr.c@ 44c4886

/*
 * Copyright (c) 2011, 2012, 2013 Dominik Taborsky
 * 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 LIBMBR_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 libmbr
 * @{
 */
/** @file MBR extraxtion library
 */

#include <async.h>
#include <assert.h>
#include <block.h>
#include <byteorder.h>
#include <errno.h>
#include <ipc/bd.h>
#include <mem.h>
#include <stdio.h>
#include <stdlib.h>

#include "libmbr.h"

static br_block_t * alloc_br(void);
static int decode_part(pt_entry_t *, mbr_part_t *, uint32_t);
static int decode_logical(mbr_label_t *, mbr_part_t *);
static void encode_part(mbr_part_t *, pt_entry_t *, uint32_t, bool);
static int check_overlap(mbr_part_t *, mbr_part_t *);
static int check_encaps(mbr_part_t *, mbr_part_t *);
static int check_preceeds(mbr_part_t *, mbr_part_t *);

/** Allocate and initialize mbr_label_t structure */
mbr_label_t * mbr_alloc_label(void)
{
        mbr_label_t *label = malloc(sizeof(mbr_label_t));
        if (label == NULL)
                return NULL;
        
        label->mbr = NULL;
        label->parts = NULL;
        label->device = 0;
        
        return label;
}

/** Free mbr_label_t structure */
void mbr_free_label(mbr_label_t *label)
{
        if (label->mbr != NULL)
                mbr_free_mbr(label->mbr);
        
        if (label->parts != NULL)
                mbr_free_partitions(label->parts);
        
        free(label);
}

/** Allocate memory for mbr_t */
mbr_t * mbr_alloc_mbr(void)
{
        return malloc(sizeof(mbr_t));
}

/** Read MBR from specific device
 * @param   label       label to write data to
 * @param   dev_handle  device to read MBR from
 *
 * @return                              EOK on success, error code on error
 */
int mbr_read_mbr(mbr_label_t *label, service_id_t dev_handle)
{       
        int rc;
        
        if (label->mbr == NULL) {
                label->mbr = mbr_alloc_mbr();
                if (label->mbr == NULL) {
                        return ENOMEM;
                }
        }

        rc = block_init(EXCHANGE_ATOMIC, dev_handle, 512);
        if (rc != EOK)
                return rc;

        rc = block_read_direct(dev_handle, 0, 1, &(label->mbr->raw_data));
        block_fini(dev_handle);
        if (rc != EOK)
                return rc;

        label->device = dev_handle;

        return EOK;
}

/** Write mbr to disk
 * @param label                 MBR to be written
 * @param dev_handle    device handle to write MBR to (may be different
 *                                                      from the device in 'mbr')
 *
 * @return                              0 on success, otherwise libblock error code
 */
int mbr_write_mbr(mbr_label_t *label, service_id_t dev_handle)
{
        int rc;

        rc = block_init(EXCHANGE_ATOMIC, dev_handle, 512);
        if (rc != EOK) {
                return rc;
        }

        rc = block_write_direct(dev_handle, 0, 1, &(label->mbr->raw_data));
        block_fini(dev_handle);
        if (rc != EOK) {
                return rc;
        }

        return EOK;
}

/** Decide whether this is an actual MBR or a Protective MBR from GPT
 *
 * @param mbr           the actual MBR to decide upon
 *
 * @return                      1 if MBR, 0 if GPT
 */
int mbr_is_mbr(mbr_label_t *label)
{
        return (label->mbr->raw_data.pte[0].ptype != PT_GPT) ? 1 : 0;
}

/** Parse partitions from MBR, freeing previous partitions if any
 * NOTE: it is assumed mbr_read_mbr(label) was called before.
 * @param label  MBR to be parsed
 *
 * @return       linked list of partitions or NULL on error
 */
int mbr_read_partitions(mbr_label_t *label)
{
        if (label == NULL || label->mbr == NULL)
                return EINVAL;
        
        int rc, rc_ext;
        unsigned int i;
        mbr_part_t *p;
        mbr_part_t *ext = NULL;
        //mbr_partitions_t *parts;
        printf("check\n");
        if (label->parts != NULL)
                mbr_free_partitions(label->parts);
        printf("check2\n");
        label->parts = mbr_alloc_partitions();
        if (label->parts == NULL) {
                return ENOMEM;
        }
        printf("primary\n");
        /* Generate the primary partitions */
        for (i = 0; i < N_PRIMARY; ++i) {
                if (label->mbr->raw_data.pte[i].ptype == PT_UNUSED)
                        continue;
                printf("pcheck1\n");
                p = mbr_alloc_partition();
                if (p == NULL) {
                        printf(LIBMBR_NAME ": Error on memory allocation.\n");
                        mbr_free_partitions(label->parts);
                        return ENOMEM;
                }
                printf("pcheck2\n");
                rc_ext = decode_part(&(label->mbr->raw_data.pte[i]), p, 0);
                mbr_set_flag(p, ST_LOGIC, false);
                rc = mbr_add_partition(label, p);
                if (rc != ERR_OK) {
                        printf(LIBMBR_NAME ": Error occured during decoding the MBR. (%d)\n" \
                               LIBMBR_NAME ": MBR is invalid.\n", rc);
                        mbr_free_partitions(label->parts);
                        return EINVAL;
                }
                printf("pcheck3\n");
                if (rc_ext) {
                        ext = p;
                        label->parts->l_extended = list_nth(&(label->parts->list), i);
                }
                printf("pcheck4\n");
        }
        printf("logical\n");
        /* Fill in the primary partitions and generate logical ones, if any */
        rc = decode_logical(label, ext);
        if (rc != EOK) {
                printf(LIBMBR_NAME ": Error occured during decoding the MBR.\n" \
                           LIBMBR_NAME ": Partition list may be incomplete.\n");
                return rc;
        }
        printf("finish\n");
        return EOK;
}

/** Write MBR and partitions to device
 * @param label        label to write
 * @param dev_handle   device to write the data to
 *
 * @return             returns EOK on succes, specific error code otherwise
 */
int mbr_write_partitions(mbr_label_t *label, service_id_t dev_handle)
{
        int i = 0;
        int rc;
        mbr_part_t *p;
        mbr_part_t *ext = (label->parts->l_extended == NULL) ? NULL
                                        : list_get_instance(label->parts->l_extended, mbr_part_t, link);
        
        rc = block_init(EXCHANGE_ATOMIC, dev_handle, 512);
        if (rc != EOK) {
                printf(LIBMBR_NAME ": Error while initializing libblock: %d - %s.\n", rc, str_error(rc));
                return rc;
        }
        
        link_t *l = label->parts->list.head.next;
        
        /* Encoding primary partitions */
        for (i = 0; i < label->parts->n_primary; i++) {
                p = list_get_instance(l, mbr_part_t, link);     
                encode_part(p, &(label->mbr->raw_data.pte[i]), 0, false);
                l = l->next;
        }
        
        /* Writing MBR */
        rc = block_write_direct(dev_handle, 0, 1, &(label->mbr->raw_data));
        if (rc != EOK) {
                printf(LIBMBR_NAME ": Error while writing MBR : %d - %s.\n", rc, str_error(rc));
                goto end;
        }
        
        if (ext == NULL)
                goto end;
        
        uint32_t base = ext->start_addr;
        mbr_part_t * prev_p;
        
        /* Note for future changes: Some thought has been put into design
         * and implementation. If you don't have to change it, don't. Other
         * designs have been tried, this came out as the least horror with
         * as much power over it as you can get. Thanks. */
        
        /* Encoding and writing first logical partition */
        if (l != &(label->parts->list.head)) {
                p = list_get_instance(l, mbr_part_t, link);
                p->ebr_addr = base;
                encode_part(p, &(p->ebr->pte[0]), base, false);
                l = l->next;
        } else {
                /* If there was an extended but no logical, we should overwrite
                 * the space where the first logical's EBR would have been. There
                 * might be some garbage from the past. */
                br_block_t * tmp = alloc_br();
                rc = block_write_direct(dev_handle, base, 1, tmp);
                if (rc != EOK) {
                        printf(LIBMBR_NAME ": Error while writing EBR: %d - %s.\n", rc, str_error(rc));
                        goto end;
                }
                free(tmp);
                goto end;
        }
        
        prev_p = p;
        
        /* Encoding and writing logical partitions */
        while (l != &(label->parts->list.head)) {
                p = list_get_instance(l, mbr_part_t, link);
                
                /* Checking whether EBR address makes sense. If not, we take a guess.
                 * So far this is simple, we just take the first preceeding sector.
                 * Fdisk always reserves at least 2048 sectors (1MiB), so it can have 
                 * the EBR aligned as well as the partition itself. Parted reserves
                 * minimum one sector, like we do.
                 * 
                 * Note that we know there is at least one sector free from previous checks.
                 * Also note that the user can set ebr_addr to their liking (if it's valid). */          
                if (p->ebr_addr >= p->start_addr || p->ebr_addr <= (prev_p->start_addr + prev_p->length)) {
                        p->ebr_addr = p->start_addr - 1;
                        DEBUG_PRINT_0(LIBMBR_NAME ": Warning: invalid EBR address.\n");
                }
                
                encode_part(p, &(p->ebr->pte[0]), p->ebr_addr, false);
                encode_part(p, &(prev_p->ebr->pte[1]), base, true);
                
                rc = block_write_direct(dev_handle, prev_p->ebr_addr, 1, prev_p->ebr);
                if (rc != EOK) {
                        printf(LIBMBR_NAME ": Error while writing EBR: %d - %s.\n", rc, str_error(rc));
                        goto end;
                }
                
                prev_p = p;
                l = l->next;
        }
        
        /* write the last EBR */
        encode_part(NULL, &(prev_p->ebr->pte[1]), 0, false);
        rc = block_write_direct(dev_handle, prev_p->ebr_addr, 1, prev_p->ebr);
        if (rc != EOK) {
                printf(LIBMBR_NAME ": Error while writing EBR: %d - %s.\n", rc, str_error(rc));
                goto end;
        }
        
        rc = EOK;
        
end:
        block_fini(dev_handle);
        
        return rc;
}

/** mbr_part_t constructor */
mbr_part_t * mbr_alloc_partition(void)
{
        mbr_part_t *p = malloc(sizeof(mbr_part_t));
        if (p == NULL) {
                return NULL;
        }
        
        link_initialize(&(p->link));
        p->ebr = NULL;
        p->type = PT_UNUSED;
        p->status = 0;
        p->start_addr = 0;
        p->length = 0;
        p->ebr_addr = 0;
        
        return p;
}

/** mbr_partitions_t constructor */
mbr_partitions_t * mbr_alloc_partitions(void)
{
        mbr_partitions_t *parts = malloc(sizeof(mbr_partitions_t));
        if (parts == NULL) {
                return NULL;
        }
        
        list_initialize(&(parts->list));
        parts->n_primary = 0;
        parts->n_logical = 0;
        parts->l_extended = NULL;
        
        /* add blank primary partitions */
        int i;
        mbr_part_t *p;
        for (i = 0; i < N_PRIMARY; ++i) {
                p = mbr_alloc_partition();
                if (p == NULL) {
                        mbr_free_partitions(parts);
                        return NULL;
                }
                list_append(&(p->link), &(parts->list));
        }
        

        return parts;
}

/** Add partition
 *      Performs checks, sorts the list.
 * 
 * @param label                 label to add to
 * @param p                             partition to add
 * 
 * @return                              ERR_OK (0) on success, other MBR_ERR_VAL otherwise
 */
mbr_err_val mbr_add_partition(mbr_label_t *label, mbr_part_t *p)
{
        int rc;
        mbr_partitions_t *parts = label->parts;
        
        aoff64_t nblocks;
        printf("add1.\n");
        rc = block_init(EXCHANGE_ATOMIC, label->device, 512);
        if (rc != EOK) {
                printf(LIBMBR_NAME ": Error while getting number of blocks: %d - %s.\n", rc, str_error(rc));
                return ERR_LIBBLOCK;
        }
        printf("add2.\n");
        rc = block_get_nblocks(label->device, &nblocks);
        block_fini(label->device);
        if (rc != EOK) {
                printf(LIBMBR_NAME ": Error while getting number of blocks: %d - %s.\n", rc, str_error(rc));
                return ERR_LIBBLOCK;
        }
        printf("add3.\n");
        if (mbr_get_flag(p, ST_LOGIC)) { 
                /* adding logical partition */
                
                /* is there any extended partition? */
                if (parts->l_extended == NULL)
                        return ERR_NO_EXTENDED;
                
                /* is the logical partition inside the extended one? */
                mbr_part_t *ext = list_get_instance(parts->l_extended, mbr_part_t, link);
                if (!check_encaps(p, ext))
                        return ERR_OUT_BOUNDS;
                
                /* find a place for the new partition in a sorted linked list */
                //mbr_part_t *last = list_get_instance(list_last(&(parts->list)), mbr_part_t, link);
                mbr_part_t *iter;
                //uint32_t ebr_space = 1;
                mbr_part_foreach(parts, iter) {
                        if (mbr_get_flag(iter, ST_LOGIC)) {
                                if (check_overlap(p, iter)) 
                                        return ERR_OVERLAP;
                                if (check_preceeds(iter, p)) {
                                        /* checking if there's at least one sector of space preceeding */
                                        if ((iter->start_addr + iter->length) >= p->start_addr - 1)
                                                return ERR_NO_EBR;
                                } else {
                                        /* checking if there's at least one sector of space following (for following partitions's EBR) */
                                        if ((p->start_addr + p->length) >= iter->start_addr - 1)
                                                return ERR_NO_EBR;
                                }
                        }
                }
                
                /* alloc EBR if it's not already there */
                if (p->ebr == NULL) {
                        p->ebr = alloc_br();
                        if (p->ebr == NULL) {
                                return ERR_NOMEM;
                        }
                }
                
                /* add it */
                list_append(&(p->link), &(parts->list));
                parts->n_logical += 1;
        } else {
                /* adding primary */
                
                if (parts->n_primary == 4) {
                        return ERR_PRIMARY_FULL;
                }
                
                /* Check if partition makes space for MBR itself. */
                if (p->start_addr == 0 || ((aoff64_t) p->start_addr) + p->length >= nblocks) {
                        return ERR_OUT_BOUNDS;
                }
                printf("add4.\n");
                /* if it's extended, is there any other one? */
                if ((p->type == PT_EXTENDED || p->type == PT_EXTENDED_LBA) && parts->l_extended != NULL) {
                        return ERR_EXTENDED_PRESENT;
                }
                printf("add5.\n");
                /* find a place and add it */
                mbr_part_t *iter;
                mbr_part_t *empty = NULL;
                mbr_part_foreach(parts, iter) {
                        printf("type: %x\n", iter->type);
                        if (iter->type == PT_UNUSED) {
                                if (empty == NULL)
                                        empty = iter;
                        } else if (check_overlap(p, iter))
                                return ERR_OVERLAP;
                }
                printf("add6. %p, %p\n", empty, p);
                list_insert_after(&(p->link), &(empty->link));
                printf("add6.1.\n");
                list_remove(&(empty->link));
                printf("add6.2.\n");
                free(empty);
                printf("add7.\n");
                parts->n_primary += 1;
                
                if (p->type == PT_EXTENDED || p->type == PT_EXTENDED_LBA)
                        parts->l_extended = &(p->link);
        }
        printf("add8.\n");
        return ERR_OK;
}

/** Remove partition
 *      Removes partition by index, indexed from zero. When removing extended
 *  partition, all logical partitions get removed as well.
 * 
 * @param label                 label to remove from
 * @param idx                   index of the partition to remove
 * 
 * @return                              EOK on success, EINVAL if idx invalid
 */
int mbr_remove_partition(mbr_label_t *label, size_t idx)
{
        link_t *l = list_nth(&(label->parts->list), idx);
        if (l == NULL)
                return EINVAL;
        
        mbr_part_t *p;
        
        /* If we're removing an extended partition, remove all logical as well */
        if (l == label->parts->l_extended) {
                label->parts->l_extended = NULL;
                
                link_t *it = l->next;
                link_t *next_it;
                while (it != &(label->parts->list.head)) {
                        next_it = it->next;
                        
                        p = list_get_instance(it, mbr_part_t, link);
                        if (mbr_get_flag(p, ST_LOGIC)) {
                                list_remove(it);
                                label->parts->n_logical -= 1;
                                mbr_free_partition(p);
                        }
                        
                        it = next_it;
                }
                
        }
        
        /* Remove the partition itself */
        p = list_get_instance(l, mbr_part_t, link);
        if (mbr_get_flag(p, ST_LOGIC)) {
                label->parts->n_logical -= 1;
                list_remove(l);
                mbr_free_partition(p);
        } else {
                /* Cannot remove primary - it would break ordering, just zero it */
                label->parts->n_primary -= 1;
                p->type = 0;
                p->status = 0;
                p->start_addr = 0;
                p->length = 0;
                p->ebr_addr = 0;
        }
        
        return EOK;
}

/** mbr_part_t destructor */
void mbr_free_partition(mbr_part_t *p)
{
        if (p->ebr != NULL)
                free(p->ebr);
        free(p);
}

/** Get flag bool value */
int mbr_get_flag(mbr_part_t *p, MBR_FLAGS flag)
{
        return (p->status & (1 << flag)) ? 1 : 0;
}

/** Set a specifig status flag to a value */
void mbr_set_flag(mbr_part_t *p, MBR_FLAGS flag, bool value)
{
        uint8_t status = p->status;

        if (value)
                status = status | (1 << flag);
        else
                status = status ^ (status & (1 << flag));

        p->status = status;
}

/** Get next aligned address (in sectors!) */
uint32_t mbr_get_next_aligned(uint32_t addr, unsigned int alignment)
{
        uint32_t div = addr / alignment;
        return (div + 1) * alignment;
}

/** Just a wrapper for free() */
void mbr_free_mbr(mbr_t *mbr)
{
        free(mbr);
}

/** Free partition list
 *
 * @param parts         partition list to be freed
 */
void mbr_free_partitions(mbr_partitions_t *parts)
{
        list_foreach_safe(parts->list, cur_link, next) {
                mbr_part_t *p = list_get_instance(cur_link, mbr_part_t, link);
                mbr_free_partition(p);
        }

        free(parts);
}

// Internal functions follow //

static br_block_t *alloc_br()
{
        br_block_t *br = malloc(sizeof(br_block_t));
        if (br == NULL)
                return NULL;
        
        memset(br, 0, 512);
        br->signature = host2uint16_t_le(BR_SIGNATURE);
        
        return br;
}

/** Parse partition entry to mbr_part_t
 * @return              returns 1, if extended partition, 0 otherwise
 * */
static int decode_part(pt_entry_t *src, mbr_part_t *trgt, uint32_t base)
{
        trgt->type = src->ptype;

        /* Checking only 0x80; otherwise writing will fix to 0x00 */
        trgt->status = (trgt->status & 0xFF00) | src->status;

        trgt->start_addr = uint32_t_le2host(src->first_lba) + base;
        trgt->length = uint32_t_le2host(src->length);

        return (src->ptype == PT_EXTENDED) ? 1 : 0;
}

/** Parse MBR contents to mbr_part_t list */
static int decode_logical(mbr_label_t *label, mbr_part_t * ext)
{
        int rc;
        mbr_part_t *p;

        if (ext == NULL)
                return EOK;

        uint32_t base = ext->start_addr;
        uint32_t addr = base;
        br_block_t *ebr;
        
        rc = block_init(EXCHANGE_ATOMIC, label->device, 512);
        if (rc != EOK)
                return rc;
        
        ebr = alloc_br();
        if (ebr == NULL) {
                rc = ENOMEM;
                goto end;
        }
        
        rc = block_read_direct(label->device, addr, 1, ebr);
        if (rc != EOK) {
                goto free_ebr_end;
        }
        
        if (uint16_t_le2host(ebr->signature) != BR_SIGNATURE) {
                rc = EINVAL;
                goto free_ebr_end;
        }
        
        if (ebr->pte[0].ptype == PT_UNUSED) {
                rc = EOK;
                goto free_ebr_end;
        }
        
        p = mbr_alloc_partition();
        if (p == NULL) {
                rc = ENOMEM;
                goto free_ebr_end;
        }
        
        decode_part(&(ebr->pte[0]), p, base);
        mbr_set_flag(p, ST_LOGIC, true);
        p->ebr = ebr;
        p->ebr_addr = addr;
        rc = mbr_add_partition(label, p);
        if (rc != ERR_OK) 
                return EINVAL;
        
        addr = uint32_t_le2host(ebr->pte[1].first_lba) + base;
        
        while (ebr->pte[1].ptype != PT_UNUSED) {
                ebr = alloc_br();
                if (ebr == NULL) {
                        rc = ENOMEM;
                        goto end;
                }
                
                rc = block_read_direct(label->device, addr, 1, ebr);
                if (rc != EOK) {
                        goto free_ebr_end;
                }
                
                if (uint16_t_le2host(ebr->signature) != BR_SIGNATURE) {
                        rc = EINVAL;
                        goto free_ebr_end;
                }
                
                p = mbr_alloc_partition();
                if (p == NULL) {
                        rc = ENOMEM;
                        goto free_ebr_end;
                }
                
                
                decode_part(&(ebr->pte[0]), p, addr);
                mbr_set_flag(p, ST_LOGIC, true);
                p->ebr = ebr;
                p->ebr_addr = addr;
                rc = mbr_add_partition(label, p);
                if (rc != ERR_OK)
                        return EINVAL;
                
                addr = uint32_t_le2host(ebr->pte[1].first_lba) + base;
        }
        
        rc = EOK;
        goto end;
        
free_ebr_end:
        free(ebr);
        
end:
        block_fini(label->device);
        
        return rc;
}

/** Convert mbr_part_t to pt_entry_t */
static void encode_part(mbr_part_t * src, pt_entry_t * trgt, uint32_t base, bool ebr)
{
        if (src != NULL) {
                //trgt->status = mbr_get_flag(src, ST_BOOT) ? B_ACTIVE : B_INACTIVE;
                trgt->status = (uint8_t) (src->status & 0xFF);
                /* ingoring CHS */
                trgt->first_chs[0] = 0xFE;
                trgt->first_chs[1] = 0xFF;
                trgt->first_chs[2] = 0xFF;
                trgt->last_chs[0] = 0xFE;
                trgt->last_chs[1] = 0xFF;
                trgt->last_chs[2] = 0xFF;
                if (ebr) {      // encoding reference to EBR
                        trgt->ptype = PT_EXTENDED_LBA;
                        trgt->first_lba = host2uint32_t_le(src->ebr_addr - base);
                        trgt->length = host2uint32_t_le(src->length + src->start_addr - src->ebr_addr);
                } else {        // encoding reference to partition
                        trgt->ptype = src->type;
                        trgt->first_lba = host2uint32_t_le(src->start_addr - base);
                        trgt->length = host2uint32_t_le(src->length);
                }
        } else {
                trgt->status = 0;
                trgt->first_chs[0] = 0;
                trgt->first_chs[1] = 0;
                trgt->first_chs[2] = 0;
                trgt->ptype = 0;
                trgt->last_chs[0] = 0;
                trgt->last_chs[1] = 0;
                trgt->last_chs[2] = 0;
                trgt->first_lba = 0;
                trgt->length = 0;
        }
}

/** Check whether two partitions overlap
 * 
 * @return              1 for yes, 0 for no
 */
static int check_overlap(mbr_part_t * p1, mbr_part_t * p2)
{
        if (p1->start_addr < p2->start_addr && p1->start_addr + p1->length < p2->start_addr) {
                return 0;
        } else if (p1->start_addr > p2->start_addr && p2->start_addr + p2->length < p1->start_addr) {
                return 0;
        }

        return 1;
}

/** Check whether one partition encapsulates the other
 * 
 * @return              1 for yes, 0 for no
 */
static int check_encaps(mbr_part_t * inner, mbr_part_t * outer)
{
        if (inner->start_addr <= outer->start_addr || outer->start_addr + outer->length <= inner->start_addr) {
                return 0;
        } else if (outer->start_addr + outer->length < inner->start_addr + inner->length) {
                return 0;
        }

        return 1;
}

/** Check whether one partition preceeds the other
 * 
 * @return              1 for yes, 0 for no
 */
static int check_preceeds(mbr_part_t * preceeder, mbr_part_t * precedee)
{
        return preceeder->start_addr < precedee->start_addr;
}