src/disk/diskimage.c

/*
 *  Copyright (C) 2003-2007  Anders Gavare.  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. 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.
 *  3. 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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.
 *
 *
 *  $Id: diskimage.c,v 1.5 2007/03/26 03:01:09 debug Exp $
 *
 *  Disk image support.
 *
 *  TODO:  diskimage_remove()? This would be useful for floppies in PC-style
 *         machines, where disks may need to be swapped during boot etc.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

#include "cpu.h"
#include "diskimage.h"
#include "machine.h"
#include "misc.h"


/*  #define debug fatal  */

extern int single_step;

static char *diskimage_types[] = DISKIMAGE_TYPES;


/**************************************************************************/

/*
 *  my_fseek():
 *
 *  A helper function, like fseek() but takes off_t.  If the system has
 *  fseeko, then that is used. Otherwise I try to fake off_t offsets here.
 *
 *  The correct position is reached by seeking 2 billion bytes at a time
 *  (or less).  Note: This method is only used for SEEK_SET, for SEEK_CUR
 *  and SEEK_END, normal fseek() is used!
 *
 *  TODO: It seemed to work on Linux/i386, but not on Solaris/sparc (?).
 *  Anyway, most modern systems have fseeko(), so it shouldn't be a problem.
 */
static int my_fseek(FILE *f, off_t offset, int whence)
{
#ifdef HACK_FSEEKO
        if (whence == SEEK_SET) {
                int res = 0;
                off_t curoff = 0;
                off_t cur_step;

                fseek(f, 0, SEEK_SET);
                while (curoff < offset) {
                        /*  How far to seek?  */
                        cur_step = offset - curoff;
                        if (cur_step > 2000000000)
                                cur_step = 2000000000;
                        res = fseek(f, cur_step, SEEK_CUR);
                        if (res)
                                return res;
                        curoff += cur_step;
                }
                return 0;
        } else
                return fseek(f, offset, whence);
#else
        return fseeko(f, offset, whence);
#endif
}


/**************************************************************************/


/*
 *  diskimage_exist():
 *
 *  Returns 1 if the specified disk id (for a specific type) exists, 0
 *  otherwise.
 */
int diskimage_exist(struct machine *machine, int id, int type)
{
        struct diskimage *d = machine->first_diskimage;

        while (d != NULL) {
                if (d->type == type && d->id == id)
                        return 1;
                d = d->next;
        }
        return 0;
}


/*
 *  diskimage_add_overlay():
 *
 *  Opens an overlay data file and its corresponding bitmap file, and adds
 *  the overlay to a disk image.
 */
void diskimage_add_overlay(struct diskimage *d, char *overlay_basename)
{
        struct diskimage_overlay overlay;
        size_t bitmap_name_len = strlen(overlay_basename) + 20;
        char *bitmap_name = malloc(bitmap_name_len);

        if (bitmap_name == NULL) {
                fprintf(stderr, "out of memory\n");
                exit(1);
        }
        snprintf(bitmap_name, bitmap_name_len, "%s.map", overlay_basename);

        overlay.overlay_basename = strdup(overlay_basename);
        overlay.f_data = fopen(overlay_basename, d->writable? "r+" : "r");
        if (overlay.f_data == NULL) {
                perror(overlay_basename);
                exit(1);
        }

        overlay.f_bitmap = fopen(bitmap_name, d->writable? "r+" : "r");
        if (overlay.f_bitmap == NULL) {
                perror(bitmap_name);
                fprintf(stderr, "Please create the map file first.\n");
                exit(1);
        }

        d->nr_of_overlays ++;
        d->overlays = realloc(d->overlays, sizeof(struct diskimage_overlay)
            * d->nr_of_overlays);
        if (d->overlays == NULL) {
                fprintf(stderr, "out of memory\n");
                exit(1);
        }

        d->overlays[d->nr_of_overlays - 1] = overlay;

        free(bitmap_name);
}


/*
 *  diskimage_recalc_size():
 *
 *  Recalculate a disk's size by stat()-ing it.
 *  d is assumed to be non-NULL.
 */
void diskimage_recalc_size(struct diskimage *d)
{
        struct stat st;
        int res;
        off_t size = 0;

        res = stat(d->fname, &st);
        if (res) {
                fprintf(stderr, "[ diskimage_recalc_size(): could not stat "
                    "'%s' ]\n", d->fname);
                return;
        }

        size = st.st_size;

        /*
         *  TODO:  CD-ROM devices, such as /dev/cd0c, how can one
         *  check how much data is on that cd-rom without reading it?
         *  For now, assume some large number, hopefully it will be
         *  enough to hold any cd-rom image.
         */
        if (d->is_a_cdrom && size == 0)
                size = 762048000;

        d->total_size = size;
        d->ncyls = d->total_size / 1048576;

        /*  TODO: There is a mismatch between d->ncyls and d->cylinders,
            SCSI-based stuff usually doesn't care.  TODO: Fix this.  */
}


/*
 *  diskimage_getsize():
 *
 *  Returns -1 if the specified disk id/type does not exists, otherwise
 *  the size of the disk image is returned.
 */
int64_t diskimage_getsize(struct machine *machine, int id, int type)
{
        struct diskimage *d = machine->first_diskimage;

        while (d != NULL) {
                if (d->type == type && d->id == id)
                        return d->total_size;
                d = d->next;
        }
        return -1;
}


/*
 *  diskimage_get_baseoffset():
 *
 *  Returns -1 if the specified disk id/type does not exists, otherwise
 *  the base offset of the disk image is returned.
 */
int64_t diskimage_get_baseoffset(struct machine *machine, int id, int type)
{
        struct diskimage *d = machine->first_diskimage;

        while (d != NULL) {
                if (d->type == type && d->id == id)
                        return d->override_base_offset;
                d = d->next;
        }
        return -1;
}


/*
 *  diskimage_getchs():
 *
 *  Returns the current CHS values of a disk image.
 */
void diskimage_getchs(struct machine *machine, int id, int type,
        int *c, int *h, int *s)
{
        struct diskimage *d = machine->first_diskimage;

        while (d != NULL) {
                if (d->type == type && d->id == id) {
                        *c = d->cylinders;
                        *h = d->heads;
                        *s = d->sectors_per_track;
                        return;
                }
                d = d->next;
        }
        fatal("diskimage_getchs(): disk id %i (type %i) not found?\n",
            id, diskimage_types[type]);
        exit(1);
}


/*
 *  diskimage_access__cdrom():
 *
 *  This is a special-case function, called from diskimage__internal_access().
 *  On my FreeBSD 4.9 system, the cdrom device /dev/cd0c seems to not be able
 *  to handle something like "fseek(512); fread(512);" but it handles
 *  "fseek(2048); fread(512);" just fine.  So, if diskimage__internal_access()
 *  fails in reading a block of data, this function is called as an attempt to
 *  align reads at 2048-byte sectors instead.
 *
 *  (Ugly hack.  TODO: how to solve this cleanly?)
 *
 *  NOTE:  Returns the number of bytes read, 0 if nothing was successfully
 *  read. (These are not the same as diskimage_access()).
 */
#define CDROM_SECTOR_SIZE       2048
static size_t diskimage_access__cdrom(struct diskimage *d, off_t offset,
        unsigned char *buf, size_t len)
{
        off_t aligned_offset;
        size_t bytes_read, total_copied = 0;
        unsigned char cdrom_buf[CDROM_SECTOR_SIZE];
        off_t buf_ofs, i = 0;

        /*  printf("diskimage_access__cdrom(): offset=0x%llx size=%lli\n",
            (long long)offset, (long long)len);  */

        aligned_offset = (offset / CDROM_SECTOR_SIZE) * CDROM_SECTOR_SIZE;
        my_fseek(d->f, aligned_offset, SEEK_SET);

        while (len != 0) {
                bytes_read = fread(cdrom_buf, 1, CDROM_SECTOR_SIZE, d->f);
                if (bytes_read != CDROM_SECTOR_SIZE)
                        return 0;

                /*  Copy (part of) cdrom_buf into buf:  */
                buf_ofs = offset - aligned_offset;
                while (buf_ofs < CDROM_SECTOR_SIZE && len != 0) {
                        buf[i ++] = cdrom_buf[buf_ofs ++];
                        total_copied ++;
                        len --;
                }

                aligned_offset += CDROM_SECTOR_SIZE;
                offset = aligned_offset;
        }

        return total_copied;
}


/*  Helper function.  */
static void overlay_set_block_in_use(struct diskimage *d,
        int overlay_nr, off_t ofs)
{
        off_t bit_nr = ofs / OVERLAY_BLOCK_SIZE;
        off_t bitmap_file_offset = bit_nr / 8;
        int res;
        unsigned char data;

        res = my_fseek(d->overlays[overlay_nr].f_bitmap,
            bitmap_file_offset, SEEK_SET);
        if (res) {
                perror("my_fseek");
                fprintf(stderr, "Could not seek in bitmap file?"
                    " offset = %lli, read\n", (long long)bitmap_file_offset);
                exit(1);
        }

        /*  Read the original bitmap data, and OR in the new bit:  */
        res = fread(&data, 1, 1, d->overlays[overlay_nr].f_bitmap);
        if (res != 1)
                data = 0x00;

        data |= (1 << (bit_nr & 7));

        /*  Write it back:  */
        res = my_fseek(d->overlays[overlay_nr].f_bitmap,
            bitmap_file_offset, SEEK_SET);
        if (res) {
                perror("my_fseek");
                fprintf(stderr, "Could not seek in bitmap file?"
                    " offset = %lli, write\n", (long long)bitmap_file_offset);
                exit(1);
        }
        res = fwrite(&data, 1, 1, d->overlays[overlay_nr].f_bitmap);
        if (res != 1) {
                fprintf(stderr, "Could not write to bitmap file. Aborting.\n");
                exit(1);
        }
}


/*  Helper function.  */
static int overlay_has_block(struct diskimage *d, int overlay_nr, off_t ofs)
{
        off_t bit_nr = ofs / OVERLAY_BLOCK_SIZE;
        off_t bitmap_file_offset = bit_nr / 8;
        int res;
        unsigned char data;

        res = my_fseek(d->overlays[overlay_nr].f_bitmap,
            bitmap_file_offset, SEEK_SET);
        if (res != 0)
                return 0;

        /*  The seek succeeded, now read the bit:  */
        res = fread(&data, 1, 1, d->overlays[overlay_nr].f_bitmap);
        if (res != 1)
                return 0;

        if (data & (1 << (bit_nr & 7)))
                return 1;

        return 0;
}


/*
 *  fwrite_helper():
 *
 *  Internal helper function. Writes to a disk image file, or if the
 *  disk image has overlays, to the last overlay.
 */
static size_t fwrite_helper(off_t offset, unsigned char *buf,
        size_t len, struct diskimage *d)
{
        off_t curofs;

        /*  Fast return-path for the case when no overlays are used:  */
        if (d->nr_of_overlays == 0) {
                int res = my_fseek(d->f, offset, SEEK_SET);
                if (res != 0) {
                        fatal("[ diskimage__internal_access(): fseek() failed"
                            " on disk id %i \n", d->id);
                        return 0;
                }

                return fwrite(buf, 1, len, d->f);
        }

        if ((len & (OVERLAY_BLOCK_SIZE-1)) != 0) {
                fatal("TODO: overlay access (write), len not multiple of "
                    "overlay block size. not yet implemented.\n");
                fatal("len = %lli\n", (long long) len);
                abort();
        }
        if ((offset & (OVERLAY_BLOCK_SIZE-1)) != 0) {
                fatal("TODO: unaligned overlay access\n");
                fatal("offset = %lli\n", (long long) offset);
                abort();
        }

        /*  Split the write into OVERLAY_BLOCK_SIZE writes:  */
        for (curofs=offset; curofs<offset+len; curofs+=OVERLAY_BLOCK_SIZE) {
                /*  Always write to the last overlay:  */
                int overlay_nr = d->nr_of_overlays-1;
                off_t lenwritten;
                int res = my_fseek(d->overlays[overlay_nr].f_data,
                    curofs, SEEK_SET);
                if (res != 0) {
                        fatal("[ diskimage__internal_access(): fseek()"
                            " failed on disk id %i \n", d->id);
                        return 0;
                }

                lenwritten = fwrite(buf, 1, OVERLAY_BLOCK_SIZE,
                    d->overlays[overlay_nr].f_data);
                buf += OVERLAY_BLOCK_SIZE;

                /*  Mark this block in the last overlay as in use:  */
                overlay_set_block_in_use(d, overlay_nr, curofs);
        }

        return len;
}


/*
 *  fread_helper():
 *
 *  Internal helper function. Reads from a disk image file, or if the
 *  disk image has overlays, from the last overlay that has the specific
 *  data (or the disk image file itself).
 */
static size_t fread_helper(off_t offset, unsigned char *buf,
        size_t len, struct diskimage *d)
{
        off_t curofs;
        size_t totallenread = 0;

        /*  Fast return-path for the case when no overlays are used:  */
        if (d->nr_of_overlays == 0) {
                int res = my_fseek(d->f, offset, SEEK_SET);
                if (res != 0) {
                        fatal("[ diskimage__internal_access(): fseek() failed"
                            " on disk id %i \n", d->id);
                        return 0;
                }

                return fread(buf, 1, len, d->f);
        }

        /*  Split the read into OVERLAY_BLOCK_SIZE reads:  */
        for (curofs=offset; len != 0;
            curofs = (curofs | (OVERLAY_BLOCK_SIZE-1)) + 1) {
                /*  Find the overlay, if any, that has this block:  */
                off_t lenread, lentoread;
                int overlay_nr;
                for (overlay_nr = d->nr_of_overlays-1;
                    overlay_nr >= 0; overlay_nr --) {
                        if (overlay_has_block(d, overlay_nr, curofs))
                                break;
                }

                lentoread = len > OVERLAY_BLOCK_SIZE? OVERLAY_BLOCK_SIZE : len;

                if (overlay_nr >= 0) {
                        /*  Read from overlay:  */
                        int res = my_fseek(d->overlays[overlay_nr].f_data,
                            curofs, SEEK_SET);
                        if (res != 0) {
                                fatal("[ diskimage__internal_access(): fseek()"
                                    " failed on disk id %i \n", d->id);
                                return 0;
                        }
                        lenread = fread(buf, 1, lentoread,
                            d->overlays[overlay_nr].f_data);
                } else {
                        /*  Read from the base disk image:  */
                        int res = my_fseek(d->f, curofs, SEEK_SET);
                        if (res != 0) {
                                fatal("[ diskimage__internal_access(): fseek()"
                                    " failed on disk id %i \n", d->id);
                                return 0;
                        }
                        lenread = fread(buf, 1, lentoread, d->f);
                }

                if (lenread != lentoread) {
                        fatal("[ INCOMPLETE READ from disk id %i, offset"
                            " %lli ]\n", d->id, (long long)curofs);
                }

                len -= lentoread;
                totallenread += lenread;
                buf += OVERLAY_BLOCK_SIZE;
        }

        return totallenread;
}


/*
 *  diskimage__internal_access():
 *
 *  Read from or write to a struct diskimage.
 *
 *  Returns 1 if the access completed successfully, 0 otherwise.
 */
int diskimage__internal_access(struct diskimage *d, int writeflag,
        off_t offset, unsigned char *buf, size_t len)
{
        ssize_t lendone;

        if (buf == NULL) {
                fprintf(stderr, "diskimage__internal_access(): buf = NULL\n");
                exit(1);
        }
        if (len == 0)
                return 1;
        if (d->f == NULL)
                return 0;

        if (writeflag) {
                if (!d->writable)
                        return 0;

                lendone = fwrite_helper(offset, buf, len, d);
        } else {
                /*
                 *  Special case for CD-ROMs. Actually, this is not needed
                 *  for .iso images, only for physical CDROMS on some OSes,
                 *  such as FreeBSD.
                 */
                if (d->is_a_cdrom)
                        lendone = diskimage_access__cdrom(d, offset, buf, len);
                else
                        lendone = fread_helper(offset, buf, len, d);

                if (lendone < (ssize_t)len)
                        memset(buf + lendone, 0, len - lendone);
        }

        /*  Incomplete data transfer? Then return failure:  */
        if (lendone != (ssize_t)len) {
#ifdef UNSTABLE_DEVEL
                fatal
#else
                debug
#endif
                    ("[ diskimage__internal_access(): disk_id %i, offset %lli"
                    ", transfer not completed. len=%i, len_done=%i ]\n",
                    d->id, (long long)offset, (int)len, (int)lendone);
                return 0;
        }

        return 1;
}


/*
 *  diskimage_access():
 *
 *  Read from or write to a disk image on a machine.
 *
 *  Returns 1 if the access completed successfully, 0 otherwise.
 */
int diskimage_access(struct machine *machine, int id, int type, int writeflag,
        off_t offset, unsigned char *buf, size_t len)
{
        struct diskimage *d = machine->first_diskimage;

        while (d != NULL) {
                if (d->type == type && d->id == id)
                        break;
                d = d->next;
        }

        if (d == NULL) {
                fatal("[ diskimage_access(): ERROR: trying to access a "
                    "non-existant %s disk image (id %i)\n",
                    diskimage_types[type], id);
                return 0;
        }

        offset -= d->override_base_offset;
        if (offset < 0 && offset + d->override_base_offset >= 0) {
                debug("[ reading before start of disk image ]\n");
                /*  Returning zeros.  */
                memset(buf, 0, len);
                return 1;
        }

        return diskimage__internal_access(d, writeflag, offset, buf, len);
}


/*
 *  diskimage_add():
 *
 *  Add a disk image.  fname is the filename of the disk image.
 *  The filename may be prefixed with one or more modifiers, followed
 *  by a colon.
 *
 *      b       specifies that this is a bootable device
 *      c       CD-ROM (instead of a normal DISK)
 *      d       DISK (this is the default)
 *      f       FLOPPY (instead of SCSI)
 *      gH;S;   set geometry (H=heads, S=sectors per track, cylinders are
 *              automatically calculated). (This is ignored for floppies.)
 *      i       IDE (instead of SCSI)
 *      oOFS;   set base offset in bytes, when booting from an ISO9660 fs
 *      r       read-only (don't allow changes to the file)
 *      s       SCSI (this is the default)
 *      t       tape
 *      V       add an overlay to a disk image
 *      0-7     force a specific SCSI ID number
 *
 *  machine is assumed to be non-NULL.
 *  Returns an integer >= 0 identifying the disk image.
 */
int diskimage_add(struct machine *machine, char *fname)
{
        struct diskimage *d, *d2;
        int id = 0, override_heads=0, override_spt=0;
        int64_t bytespercyl, override_base_offset=0;
        char *cp;
        int prefix_b=0, prefix_c=0, prefix_d=0, prefix_f=0, prefix_g=0;
        int prefix_i=0, prefix_r=0, prefix_s=0, prefix_t=0, prefix_id=-1;
        int prefix_o=0, prefix_V=0;

        if (fname == NULL) {
                fprintf(stderr, "diskimage_add(): NULL ptr\n");
                return 0;
        }

        /*  Get prefix from fname:  */
        cp = strchr(fname, ':');
        if (cp != NULL) {
                while (fname <= cp) {
                        char c = *fname++;
                        switch (c) {
                        case '0':
                        case '1':
                        case '2':
                        case '3':
                        case '4':
                        case '5':
                        case '6':
                        case '7':
                                prefix_id = c - '0';
                                break;
                        case 'b':
                                prefix_b = 1;
                                break;
                        case 'c':
                                prefix_c = 1;
                                break;
                        case 'd':
                                prefix_d = 1;
                                break;
                        case 'f':
                                prefix_f = 1;
                                break;
                        case 'g':
                                prefix_g = 1;
                                override_heads = atoi(fname);
                                while (*fname != '\0' && *fname != ';')
                                        fname ++;
                                if (*fname == ';')
                                        fname ++;
                                override_spt = atoi(fname);
                                while (*fname != '\0' && *fname != ';' &&
                                    *fname != ':')
                                        fname ++;
                                if (*fname == ';')
                                        fname ++;
                                if (override_heads < 1 ||
                                    override_spt < 1) {
                                        fatal("Bad geometry: heads=%i "
                                            "spt=%i\n", override_heads,
                                            override_spt);
                                        exit(1);
                                }
                                break;
                        case 'i':
                                prefix_i = 1;
                                break;
                        case 'o':
                                prefix_o = 1;
                                override_base_offset = atoi(fname);
                                while (*fname != '\0' && *fname != ':'
                                    && *fname != ';')
                                        fname ++;
                                if (*fname == ':' || *fname == ';')
                                        fname ++;
                                if (override_base_offset < 0) {
                                        fatal("Bad base offset: %"PRIi64
                                            "\n", override_base_offset);
                                        exit(1);
                                }
                                break;
                        case 'r':
                                prefix_r = 1;
                                break;
                        case 's':
                                prefix_s = 1;
                                break;
                        case 't':
                                prefix_t = 1;
                                break;
                        case 'V':
                                prefix_V = 1;
                                break;
                        case ':':
                                break;
                        default:
                                fprintf(stderr, "diskimage_add(): invalid "
                                    "prefix char '%c'\n", c);
                                exit(1);
                        }
                }
        }

        /*  Allocate a new diskimage struct:  */
        d = malloc(sizeof(struct diskimage));
        if (d == NULL) {
                fprintf(stderr, "out of memory in diskimage_add()\n");
                exit(1);
        }
        memset(d, 0, sizeof(struct diskimage));

        /*  Default to IDE disks...  */
        d->type = DISKIMAGE_IDE;

        /*  ... but some machines use SCSI by default:  */
        if (machine->machine_type == MACHINE_PMAX ||
            machine->machine_type == MACHINE_ARC)
                d->type = DISKIMAGE_SCSI;

        if (prefix_i + prefix_f + prefix_s > 1) {
                fprintf(stderr, "Invalid disk image prefix(es). You can"
                    "only use one of i, f, and s\nfor each disk image.\n");
                exit(1);
        }

        if (prefix_i)
                d->type = DISKIMAGE_IDE;
        if (prefix_f)
                d->type = DISKIMAGE_FLOPPY;
        if (prefix_s)
                d->type = DISKIMAGE_SCSI;

        /*  Special case: Add an overlay for an already added disk image:  */
        if (prefix_V) {
                struct diskimage *dx = machine->first_diskimage;

                if (prefix_id < 0) {
                        fprintf(stderr, "The 'V' disk image prefix requires"
                            " a disk ID to also be supplied.\n");
                        exit(1);
                }

                while (dx != NULL) {
                        if (d->type == dx->type && prefix_id == dx->id)
                                break;
                        dx = dx->next;
                }

                if (dx == NULL) {
                        fprintf(stderr, "Bad ID supplied for overlay?\n");
                        exit(1);
                }

                diskimage_add_overlay(dx, fname);

                /*  Free the preliminary d struct:  */
                free(d);

                /*  Don't add any disk image. This is an overlay!  */
                return -1;
        }

        /*  Add the new disk image in the disk image chain:  */
        d2 = machine->first_diskimage;
        if (d2 == NULL) {
                machine->first_diskimage = d;
        } else {
                while (d2->next != NULL)
                        d2 = d2->next;
                d2->next = d;
        }

        if (prefix_o)
                d->override_base_offset = override_base_offset;

        d->fname = strdup(fname);
        if (d->fname == NULL) {
                fprintf(stderr, "out of memory\n");
                exit(1);
        }

        d->logical_block_size = 512;

        /*
         *  Is this a tape, CD-ROM or a normal disk?
         *
         *  An intelligent guess, if no prefixes are used, would be that
         *  filenames ending with .iso or .cdr are CD-ROM images.
         */
        if (prefix_t) {
                d->is_a_tape = 1;
        } else {
                if (prefix_c ||
                    ((strlen(d->fname) > 4 &&
                    (strcasecmp(d->fname + strlen(d->fname) - 4, ".cdr") == 0 ||
                    strcasecmp(d->fname + strlen(d->fname) - 4, ".iso") == 0))
                    && !prefix_d)
                   ) {
                        d->is_a_cdrom = 1;

                        /*
                         *  This is tricky. Should I use 512 or 2048 here?
                         *  NetBSD/pmax 1.6.2 and Ultrix likes 512 bytes
                         *  per sector, but NetBSD 2.0_BETA suddenly ignores
                         *  this value and uses 2048 instead.
                         *
                         *  OpenBSD/arc doesn't like 2048, it requires 512
                         *  to work correctly.
                         *
                         *  TODO
                         */

#if 0
                        if (machine->machine_type == MACHINE_PMAX)
                                d->logical_block_size = 512;
                        else
                                d->logical_block_size = 2048;
#endif
                        d->logical_block_size = 512;
                }
        }

        diskimage_recalc_size(d);

        if ((d->total_size == 720*1024 || d->total_size == 1474560
            || d->total_size == 2949120 || d->total_size == 1228800)
            && !prefix_i && !prefix_s)
                d->type = DISKIMAGE_FLOPPY;

        switch (d->type) {
        case DISKIMAGE_FLOPPY:
                if (d->total_size < 737280) {
                        fatal("\nTODO: small (non-80-cylinder) floppies?\n\n");
                        exit(1);
                }
                d->cylinders = 80;
                d->heads = 2;
                d->sectors_per_track = d->total_size / (d->cylinders *
                    d->heads * 512);
                break;
        default:/*  Non-floppies:  */
                d->heads = 16;
                d->sectors_per_track = 63;
                if (prefix_g) {
                        d->chs_override = 1;
                        d->heads = override_heads;
                        d->sectors_per_track = override_spt;
                }
                bytespercyl = d->heads * d->sectors_per_track * 512;
                d->cylinders = d->total_size / bytespercyl;
                if (d->cylinders * bytespercyl < d->total_size)
                        d->cylinders ++;
        }

        d->rpms = 3600;

        if (prefix_b)
                d->is_boot_device = 1;

        d->writable = access(fname, W_OK) == 0? 1 : 0;

        if (d->is_a_cdrom || prefix_r)
                d->writable = 0;

        d->f = fopen(fname, d->writable? "r+" : "r");
        if (d->f == NULL) {
                perror(fname);
                exit(1);
        }

        /*  Calculate which ID to use:  */
        if (prefix_id == -1) {
                int free = 0, collision = 1;

                while (collision) {
                        collision = 0;
                        d2 = machine->first_diskimage;
                        while (d2 != NULL) {
                                /*  (don't compare against ourselves :)  */
                                if (d2 == d) {
                                        d2 = d2->next;
                                        continue;
                                }
                                if (d2->id == free && d2->type == d->type) {
                                        collision = 1;
                                        break;
                                }
                                d2 = d2->next;
                        }
                        if (!collision)
                                id = free;
                        else
                                free ++;
                }
        } else {
                id = prefix_id;
                d2 = machine->first_diskimage;
                while (d2 != NULL) {
                        /*  (don't compare against ourselves :)  */
                        if (d2 == d) {
                                d2 = d2->next;
                                continue;
                        }
                        if (d2->id == id && d2->type == d->type) {
                                fprintf(stderr, "disk image id %i "
                                    "already in use\n", id);
                                exit(1);
                        }
                        d2 = d2->next;
                }
        }

        d->id = id;

        return id;
}


/*
 *  diskimage_bootdev():
 *
 *  Returns the disk id of the device which we're booting from.  If typep is
 *  non-NULL, the type is returned as well.
 *
 *  If no disk was used as boot device, then -1 is returned. (In practice,
 *  this is used to fake network (tftp) boot.)
 */
int diskimage_bootdev(struct machine *machine, int *typep)
{
        struct diskimage *d;

        d = machine->first_diskimage;
        while (d != NULL) {
                if (d->is_boot_device) {
                        if (typep != NULL)
                                *typep = d->type;
                        return d->id;
                }
                d = d->next;
        }

        d = machine->first_diskimage;
        if (d != NULL) {
                if (typep != NULL)
                        *typep = d->type;
                return d->id;
        }

        return -1;
}


/*
 *  diskimage_getname():
 *
 *  Returns 1 if a valid disk image name was returned, 0 otherwise.
 */
int diskimage_getname(struct machine *machine, int id, int type,
        char *buf, size_t bufsize)
{
        struct diskimage *d = machine->first_diskimage;

        if (buf == NULL)
                return 0;

        while (d != NULL) {
                if (d->type == type && d->id == id) {
                        char *p = strrchr(d->fname, '/');
                        if (p == NULL)
                                p = d->fname;
                        else
                                p ++;
                        snprintf(buf, bufsize, "%s", p);
                        return 1;
                }
                d = d->next;
        }
        return 0;
}


/*
 *  diskimage_is_a_cdrom():
 *
 *  Returns 1 if a disk image is a CDROM, 0 otherwise.
 */
int diskimage_is_a_cdrom(struct machine *machine, int id, int type)
{
        struct diskimage *d = machine->first_diskimage;

        while (d != NULL) {
                if (d->type == type && d->id == id)
                        return d->is_a_cdrom;
                d = d->next;
        }
        return 0;
}


/*
 *  diskimage_is_a_tape():
 *
 *  Returns 1 if a disk image is a tape, 0 otherwise.
 *
 *  (Used in src/machine.c, to select 'rz' vs 'tz' for DECstation
 *  boot strings.)
 */
int diskimage_is_a_tape(struct machine *machine, int id, int type)
{
        struct diskimage *d = machine->first_diskimage;

        while (d != NULL) {
                if (d->type == type && d->id == id)
                        return d->is_a_tape;
                d = d->next;
        }
        return 0;
}


/*
 *  diskimage_dump_info():
 *
 *  Debug dump of all diskimages that are loaded for a specific machine.
 */
void diskimage_dump_info(struct machine *machine)
{
        int i, iadd = DEBUG_INDENTATION;
        struct diskimage *d = machine->first_diskimage;

        while (d != NULL) {
                debug("diskimage: %s\n", d->fname);
                debug_indentation(iadd);

                switch (d->type) {
                case DISKIMAGE_SCSI:
                        debug("SCSI");
                        break;
                case DISKIMAGE_IDE:
                        debug("IDE");
                        break;
                case DISKIMAGE_FLOPPY:
                        debug("FLOPPY");
                        break;
                default:
                        debug("UNKNOWN type %i", d->type);
                }

                debug(" %s", d->is_a_tape? "TAPE" :
                        (d->is_a_cdrom? "CD-ROM" : "DISK"));
                debug(" id %i, ", d->id);
                debug("%s, ", d->writable? "read/write" : "read-only");

                if (d->type == DISKIMAGE_FLOPPY)
                        debug("%lli KB", (long long) (d->total_size / 1024));
                else
                        debug("%lli MB", (long long) (d->total_size / 1048576));

                if (d->type == DISKIMAGE_FLOPPY || d->chs_override)
                        debug(" (CHS=%i,%i,%i)", d->cylinders, d->heads,
                            d->sectors_per_track);
                else
                        debug(" (%lli sectors)", (long long)
                           (d->total_size / 512));

                if (d->is_boot_device)
                        debug(" (BOOT)");
                debug("\n");

                for (i=0; i<d->nr_of_overlays; i++) {
                        debug("overlay %i: %s\n",
                            i, d->overlays[i].overlay_basename);
                }

                debug_indentation(-iadd);

                d = d->next;
        }
}
