// SPDX-License-Identifier: GPL-2.0
/* This utility makes a bootblock suitable for the SRM console/miniloader */

/* Usage:
 *      mkbb <device> <lxboot>
 *
 * Where <device> is the name of the device to install the bootblock on,
 * and <lxboot> is the name of a bootblock to merge in.  This bootblock
 * contains the offset and size of the bootloader.  It must be exactly
 * 512 bytes long.
 */

#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

/* Minimal definition of disklabel, so we don't have to include
 * asm/disklabel.h (confuses make)
 */
#ifndef MAXPARTITIONS
#define MAXPARTITIONS   8                       /* max. # of partitions */
#endif

#ifndef u8
#define u8 unsigned char
#endif

#ifndef u16
#define u16 unsigned short
#endif

#ifndef u32
#define u32 unsigned int
#endif

struct disklabel {
    u32 d_magic;                                /* must be DISKLABELMAGIC */
    u16 d_type, d_subtype;
    u8  d_typename[16];
    u8  d_packname[16];
    u32 d_secsize;
    u32 d_nsectors;
    u32 d_ntracks;
    u32 d_ncylinders;
    u32 d_secpercyl;
    u32 d_secprtunit;
    u16 d_sparespertrack;
    u16 d_sparespercyl;
    u32 d_acylinders;
    u16 d_rpm, d_interleave, d_trackskew, d_cylskew;
    u32 d_headswitch, d_trkseek, d_flags;
    u32 d_drivedata[5];
    u32 d_spare[5];
    u32 d_magic2;                               /* must be DISKLABELMAGIC */
    u16 d_checksum;
    u16 d_npartitions;
    u32 d_bbsize, d_sbsize;
    struct d_partition {
        u32     p_size;
        u32     p_offset;
        u32     p_fsize;
        u8      p_fstype;
        u8      p_frag;
        u16     p_cpg;
    } d_partitions[MAXPARTITIONS];
};


typedef union __bootblock {
    struct {
        char                    __pad1[64];
        struct disklabel        __label;
    } __u1;
    struct {
        unsigned long           __pad2[63];
        unsigned long           __checksum;
    } __u2;
    char                bootblock_bytes[512];
    unsigned long       bootblock_quadwords[64];
} bootblock;

#define bootblock_label         __u1.__label
#define bootblock_checksum      __u2.__checksum

int main(int argc, char ** argv)
{
    bootblock           bootblock_from_disk;
    bootblock           bootloader_image;
    int                 dev, fd;
    int                 i;
    int                 nread;

    /* Make sure of the arg count */
    if(argc != 3) {
        fprintf(stderr, "Usage: %s device lxboot\n", argv[0]);
        exit(0);
    }

    /* First, open the device and make sure it's accessible */
    dev = open(argv[1], O_RDWR);
    if(dev < 0) {
        perror(argv[1]);
        exit(0);
    }

    /* Now open the lxboot and make sure it's reasonable */
    fd = open(argv[2], O_RDONLY);
    if(fd < 0) {
        perror(argv[2]);
        close(dev);
        exit(0);
    }

    /* Read in the lxboot */
    nread = read(fd, &bootloader_image, sizeof(bootblock));
    if(nread != sizeof(bootblock)) {
        perror("lxboot read");
        fprintf(stderr, "expected %zd, got %d\n", sizeof(bootblock), nread);
        exit(0);
    }

    /* Read in the bootblock from disk. */
    nread = read(dev, &bootblock_from_disk, sizeof(bootblock));
    if(nread != sizeof(bootblock)) {
        perror("bootblock read");
        fprintf(stderr, "expected %zd, got %d\n", sizeof(bootblock), nread);
        exit(0);
    }

    /* Swap the bootblock's disklabel into the bootloader */
    bootloader_image.bootblock_label = bootblock_from_disk.bootblock_label;

    /* Calculate the bootblock checksum */
    bootloader_image.bootblock_checksum = 0;
    for(i = 0; i < 63; i++) {
        bootloader_image.bootblock_checksum += 
                        bootloader_image.bootblock_quadwords[i];
    }

    /* Write the whole thing out! */
    lseek(dev, 0L, SEEK_SET);
    if(write(dev, &bootloader_image, sizeof(bootblock)) != sizeof(bootblock)) {
        perror("bootblock write");
        exit(0);
    }

    close(fd);
    close(dev);
    exit(0);
}