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path: root/com32/chain/utility.c
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#include <com32.h>
#include <stdint.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <syslinux/disk.h>
#include "utility.h"

static const char *bpbtypes[] = {
    [0] =  "unknown",
    [1] =  "2.0",
    [2] =  "3.0",
    [3] =  "3.2",
    [4] =  "3.4",
    [5] =  "4.0",
    [6] =  "8.0 (NT+)",
    [7] =  "7.0",
};

void error(const char *msg)
{
    fputs(msg, stderr);
}

int guid_is0(const struct guid *guid)
{
    return !*(const uint64_t *)guid && !*((const uint64_t *)guid + 1);
}

void wait_key(void)
{
    int cnt;
    char junk;

    /* drain */
    do {
	errno = 0;
	cnt = read(0, &junk, 1);
    } while (cnt > 0 || (cnt < 0 && errno == EAGAIN));

    /* wait */
    do {
	errno = 0;
	cnt = read(0, &junk, 1);
    } while (!cnt || (cnt < 0 && errno == EAGAIN));
}

uint32_t lba2chs(const struct disk_info *di, uint64_t lba, uint32_t mode)
{
    uint32_t c, h, s, t;
    uint32_t cs, hs, ss;

    /*
     * Not much reason here, but if we have no valid CHS geometry, we assume
     * "typical" ones to have something to return.
     */
    if (di->cbios) {
	cs = di->cyl;
	hs = di->head;
	ss = di->spt;
	if (mode == l2c_cadd && cs < 1024 && di->lbacnt > cs*hs*ss)
	    cs++;
	else if (mode == l2c_cmax)
	    cs = 1024;
    } else {
	if (di->disk & 0x80) {
	    cs = 1024;
	    hs = 255;
	    ss = 63;
	} else {
	    cs = 80;
	    hs = 2;
	    ss = 18;
	}
    }

    if (lba >= cs*hs*ss) {
	s = ss;
	h = hs - 1;
	c = cs - 1;
    } else {
	s = ((uint32_t)lba % ss) + 1;
	t = (uint32_t)lba / ss;
	h = t % hs;
	c = t / hs;
    }

    return h | (s << 8) | ((c & 0x300) << 6) | ((c & 0xFF) << 16);
}

uint32_t get_file_lba(const char *filename)
{
    com32sys_t inregs;
    uint32_t lba;

    /* Start with clean registers */
    memset(&inregs, 0, sizeof(com32sys_t));

    /* Put the filename in the bounce buffer */
    strlcpy(__com32.cs_bounce, filename, __com32.cs_bounce_size);

    /* Call comapi_open() which returns a structure pointer in SI
     * to a structure whose first member happens to be the LBA.
     */
    inregs.eax.w[0] = 0x0006;
    inregs.esi.w[0] = OFFS(__com32.cs_bounce);
    inregs.es = SEG(__com32.cs_bounce);
    __com32.cs_intcall(0x22, &inregs, &inregs);

    if ((inregs.eflags.l & EFLAGS_CF) || inregs.esi.w[0] == 0) {
	return 0;		/* Filename not found */
    }

    /* Since the first member is the LBA, we simply cast */
    lba = *((uint32_t *) MK_PTR(inregs.ds, inregs.esi.w[0]));

    /* Clean the registers for the next call */
    memset(&inregs, 0, sizeof(com32sys_t));

    /* Put the filename in the bounce buffer */
    strlcpy(__com32.cs_bounce, filename, __com32.cs_bounce_size);

    /* Call comapi_close() to free the structure */
    inregs.eax.w[0] = 0x0008;
    inregs.esi.w[0] = OFFS(__com32.cs_bounce);
    inregs.es = SEG(__com32.cs_bounce);
    __com32.cs_intcall(0x22, &inregs, &inregs);

    return lba;
}

/* drive offset detection */
int drvoff_detect(int type, unsigned int *off)
{
    if (bpbV40 <= type && type <= bpbVNT) {
	*off = 0x24;
    } else if (type == bpbV70) {
	*off = 0x40;
    } else
	return 0;

    return -1;
}

/*
 * heuristics could certainly be improved
 */
int bpb_detect(const uint8_t *sec, const char *tag)
{
    int a, b, c, jmp = -1, rev = 0;

    /* media descriptor check */
    if ((sec[0x15] & 0xF0) != 0xF0)
	goto out;

    if (sec[0] == 0xEB)	/* jump short */
	jmp = 2 + *(int8_t *)(sec + 1);
    else if (sec[0] == 0xE9) /* jump near */
	jmp = 3 + *(int16_t *)(sec + 1);

    if (jmp < 0)    /* no boot code at all ? */
	goto nocode;

    /* sanity */
    if (jmp < 0x18 || jmp > 0x1F0)
	goto out;

    /* detect by jump */
    if (jmp >= 0x18 && jmp < 0x1E)
	rev = bpbV20;
    else if (jmp >= 0x1E && jmp < 0x20)
	rev = bpbV30;
    else if (jmp >= 0x20 && jmp < 0x24)
	rev = bpbV32;
    else if (jmp >= 0x24 && jmp < 0x46)
	rev = bpbV34;

    /* TODO: some better V2 - V3.4 checks ? */

    if (rev)
	goto out;
    /*
     * BPB info:
     * 2.0 ==       0x0B - 0x17
     * 3.0 == 2.0 + 0x18 - 0x1D
     * 3.2 == 3.0 + 0x1E - 0x1F
     * 3.4 ==!2.0 + 0x18 - 0x23
     * 4.0 == 3.4 + 0x24 - 0x45
     *  NT ==~3.4 + 0x24 - 0x53
     * 7.0 == 3.4 + 0x24 - 0x59
     */

nocode:
    a = memcmp(sec + 0x03, "NTFS", 4);
    b = memcmp(sec + 0x36, "FAT", 3);
    c = memcmp(sec + 0x52, "FAT", 3);	/* ext. DOS 7+ bs */

    if ((sec[0x26] & 0xFE) == 0x28 && !b) {
	rev = bpbV40;
    } else if (sec[0x26] == 0x80 && !a) {
	rev = bpbVNT;
    } else if ((sec[0x42] & 0xFE) == 0x28 && !c) {
	rev = bpbV70;
    }

out:
    printf("BPB detection (%s): %s\n", tag, bpbtypes[rev]);
    return rev;
}

/* vim: set ts=8 sts=4 sw=4 noet: */