summaryrefslogtreecommitdiffstats
path: root/qemu/roms/seabios/src/boot.c
blob: f23e9e154ea21e9170c164646526436c9dd7787d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
// Code to load disk image and start system boot.
//
// Copyright (C) 2008-2013  Kevin O'Connor <kevin@koconnor.net>
// Copyright (C) 2002  MandrakeSoft S.A.
//
// This file may be distributed under the terms of the GNU LGPLv3 license.

#include "block.h" // struct drive_s
#include "bregs.h" // struct bregs
#include "config.h" // CONFIG_*
#include "fw/paravirt.h" // qemu_cfg_show_boot_menu
#include "hw/pci.h" // pci_bdf_to_*
#include "hw/rtc.h" // rtc_read
#include "hw/usb.h" // struct usbdevice_s
#include "list.h" // hlist_node
#include "malloc.h" // free
#include "output.h" // dprintf
#include "romfile.h" // romfile_loadint
#include "std/disk.h" // struct mbr_s
#include "string.h" // memset
#include "util.h" // irqtimer_calc


/****************************************************************
 * Boot priority ordering
 ****************************************************************/

static char **Bootorder VARVERIFY32INIT;
static int BootorderCount;

static void
loadBootOrder(void)
{
    if (!CONFIG_BOOTORDER)
        return;

    char *f = romfile_loadfile("bootorder", NULL);
    if (!f)
        return;

    int i = 0;
    BootorderCount = 1;
    while (f[i]) {
        if (f[i] == '\n')
            BootorderCount++;
        i++;
    }
    Bootorder = malloc_tmphigh(BootorderCount*sizeof(char*));
    if (!Bootorder) {
        warn_noalloc();
        free(f);
        BootorderCount = 0;
        return;
    }

    dprintf(1, "boot order:\n");
    i = 0;
    do {
        Bootorder[i] = f;
        f = strchr(f, '\n');
        if (f)
            *(f++) = '\0';
        Bootorder[i] = nullTrailingSpace(Bootorder[i]);
        dprintf(1, "%d: %s\n", i+1, Bootorder[i]);
        i++;
    } while (f);
}

// See if 'str' starts with 'glob' - if glob contains an '*' character
// it will match any number of characters in str that aren't a '/' or
// the next glob character.
static char *
glob_prefix(const char *glob, const char *str)
{
    for (;;) {
        if (!*glob && (!*str || *str == '/'))
            return (char*)str;
        if (*glob == '*') {
            if (!*str || *str == '/' || *str == glob[1])
                glob++;
            else
                str++;
            continue;
        }
        if (*glob != *str)
            return NULL;
        glob++;
        str++;
    }
}

// Search the bootorder list for the given glob pattern.
static int
find_prio(const char *glob)
{
    dprintf(1, "Searching bootorder for: %s\n", glob);
    int i;
    for (i = 0; i < BootorderCount; i++)
        if (glob_prefix(glob, Bootorder[i]))
            return i+1;
    return -1;
}

#define FW_PCI_DOMAIN "/pci@i0cf8"

static char *
build_pci_path(char *buf, int max, const char *devname, struct pci_device *pci)
{
    // Build the string path of a bdf - for example: /pci@i0cf8/isa@1,2
    char *p = buf;
    if (pci->parent) {
        p = build_pci_path(p, max, "pci-bridge", pci->parent);
    } else {
        if (pci->rootbus)
            p += snprintf(p, max, "/pci-root@%x", pci->rootbus);
        p += snprintf(p, buf+max-p, "%s", FW_PCI_DOMAIN);
    }

    int dev = pci_bdf_to_dev(pci->bdf), fn = pci_bdf_to_fn(pci->bdf);
    p += snprintf(p, buf+max-p, "/%s@%x", devname, dev);
    if (fn)
        p += snprintf(p, buf+max-p, ",%x", fn);
    return p;
}

int bootprio_find_pci_device(struct pci_device *pci)
{
    if (CONFIG_CSM)
        return csm_bootprio_pci(pci);
    if (!CONFIG_BOOTORDER)
        return -1;
    // Find pci device - for example: /pci@i0cf8/ethernet@5
    char desc[256];
    build_pci_path(desc, sizeof(desc), "*", pci);
    return find_prio(desc);
}

int bootprio_find_scsi_device(struct pci_device *pci, int target, int lun)
{
    if (!CONFIG_BOOTORDER)
        return -1;
    if (!pci)
        // support only pci machine for now
        return -1;
    // Find scsi drive - for example: /pci@i0cf8/scsi@5/channel@0/disk@1,0
    char desc[256], *p;
    p = build_pci_path(desc, sizeof(desc), "*", pci);
    snprintf(p, desc+sizeof(desc)-p, "/*@0/*@%x,%x", target, lun);
    return find_prio(desc);
}

int bootprio_find_ata_device(struct pci_device *pci, int chanid, int slave)
{
    if (CONFIG_CSM)
        return csm_bootprio_ata(pci, chanid, slave);
    if (!CONFIG_BOOTORDER)
        return -1;
    if (!pci)
        // support only pci machine for now
        return -1;
    // Find ata drive - for example: /pci@i0cf8/ide@1,1/drive@1/disk@0
    char desc[256], *p;
    p = build_pci_path(desc, sizeof(desc), "*", pci);
    snprintf(p, desc+sizeof(desc)-p, "/drive@%x/disk@%x", chanid, slave);
    return find_prio(desc);
}

int bootprio_find_fdc_device(struct pci_device *pci, int port, int fdid)
{
    if (CONFIG_CSM)
        return csm_bootprio_fdc(pci, port, fdid);
    if (!CONFIG_BOOTORDER)
        return -1;
    if (!pci)
        // support only pci machine for now
        return -1;
    // Find floppy - for example: /pci@i0cf8/isa@1/fdc@03f1/floppy@0
    char desc[256], *p;
    p = build_pci_path(desc, sizeof(desc), "isa", pci);
    snprintf(p, desc+sizeof(desc)-p, "/fdc@%04x/floppy@%x", port, fdid);
    return find_prio(desc);
}

int bootprio_find_pci_rom(struct pci_device *pci, int instance)
{
    if (!CONFIG_BOOTORDER)
        return -1;
    // Find pci rom - for example: /pci@i0cf8/scsi@3:rom2
    char desc[256], *p;
    p = build_pci_path(desc, sizeof(desc), "*", pci);
    if (instance)
        snprintf(p, desc+sizeof(desc)-p, ":rom%x", instance);
    return find_prio(desc);
}

int bootprio_find_named_rom(const char *name, int instance)
{
    if (!CONFIG_BOOTORDER)
        return -1;
    // Find named rom - for example: /rom@genroms/linuxboot.bin
    char desc[256], *p;
    p = desc + snprintf(desc, sizeof(desc), "/rom@%s", name);
    if (instance)
        snprintf(p, desc+sizeof(desc)-p, ":rom%x", instance);
    return find_prio(desc);
}

static char *
build_usb_path(char *buf, int max, struct usbhub_s *hub)
{
    if (!hub->usbdev)
        // Root hub - nothing to add.
        return buf;
    char *p = build_usb_path(buf, max, hub->usbdev->hub);
    p += snprintf(p, buf+max-p, "/hub@%x", hub->usbdev->port+1);
    return p;
}

int bootprio_find_usb(struct usbdevice_s *usbdev, int lun)
{
    if (!CONFIG_BOOTORDER)
        return -1;
    // Find usb - for example: /pci@i0cf8/usb@1,2/storage@1/channel@0/disk@0,0
    char desc[256], *p;
    p = build_pci_path(desc, sizeof(desc), "usb", usbdev->hub->cntl->pci);
    p = build_usb_path(p, desc+sizeof(desc)-p, usbdev->hub);
    snprintf(p, desc+sizeof(desc)-p, "/storage@%x/*@0/*@0,%x"
             , usbdev->port+1, lun);
    int ret = find_prio(desc);
    if (ret >= 0)
        return ret;
    // Try usb-host/redir - for example: /pci@i0cf8/usb@1,2/usb-host@1
    snprintf(p, desc+sizeof(desc)-p, "/usb-*@%x", usbdev->port+1);
    return find_prio(desc);
}


/****************************************************************
 * Boot setup
 ****************************************************************/

static int BootRetryTime;
static int CheckFloppySig = 1;

#define DEFAULT_PRIO           9999

static int DefaultFloppyPrio = 101;
static int DefaultCDPrio     = 102;
static int DefaultHDPrio     = 103;
static int DefaultBEVPrio    = 104;

void
boot_init(void)
{
    if (! CONFIG_BOOT)
        return;

    if (CONFIG_QEMU) {
        // On emulators, get boot order from nvram.
        if (rtc_read(CMOS_BIOS_BOOTFLAG1) & 1)
            CheckFloppySig = 0;
        u32 bootorder = (rtc_read(CMOS_BIOS_BOOTFLAG2)
                         | ((rtc_read(CMOS_BIOS_BOOTFLAG1) & 0xf0) << 4));
        DefaultFloppyPrio = DefaultCDPrio = DefaultHDPrio
            = DefaultBEVPrio = DEFAULT_PRIO;
        int i;
        for (i=101; i<104; i++) {
            u32 val = bootorder & 0x0f;
            bootorder >>= 4;
            switch (val) {
            case 1: DefaultFloppyPrio = i; break;
            case 2: DefaultHDPrio = i;     break;
            case 3: DefaultCDPrio = i;     break;
            case 4: DefaultBEVPrio = i;    break;
            }
        }
    }

    BootRetryTime = romfile_loadint("etc/boot-fail-wait", 60*1000);

    loadBootOrder();
}


/****************************************************************
 * BootList handling
 ****************************************************************/

struct bootentry_s {
    int type;
    union {
        u32 data;
        struct segoff_s vector;
        struct drive_s *drive;
    };
    int priority;
    const char *description;
    struct hlist_node node;
};
static struct hlist_head BootList VARVERIFY32INIT;

#define IPL_TYPE_FLOPPY      0x01
#define IPL_TYPE_HARDDISK    0x02
#define IPL_TYPE_CDROM       0x03
#define IPL_TYPE_CBFS        0x20
#define IPL_TYPE_BEV         0x80
#define IPL_TYPE_BCV         0x81
#define IPL_TYPE_HALT        0xf0

static void
bootentry_add(int type, int prio, u32 data, const char *desc)
{
    if (! CONFIG_BOOT)
        return;
    struct bootentry_s *be = malloc_tmp(sizeof(*be));
    if (!be) {
        warn_noalloc();
        return;
    }
    be->type = type;
    be->priority = prio;
    be->data = data;
    be->description = desc ?: "?";
    dprintf(3, "Registering bootable: %s (type:%d prio:%d data:%x)\n"
            , be->description, type, prio, data);

    // Add entry in sorted order.
    struct hlist_node **pprev;
    struct bootentry_s *pos;
    hlist_for_each_entry_pprev(pos, pprev, &BootList, node) {
        if (be->priority < pos->priority)
            break;
        if (be->priority > pos->priority)
            continue;
        if (be->type < pos->type)
            break;
        if (be->type > pos->type)
            continue;
        if (be->type <= IPL_TYPE_CDROM
            && (be->drive->type < pos->drive->type
                || (be->drive->type == pos->drive->type
                    && be->drive->cntl_id < pos->drive->cntl_id)))
            break;
    }
    hlist_add(&be->node, pprev);
}

// Return the given priority if it's set - defaultprio otherwise.
static inline int defPrio(int priority, int defaultprio) {
    return (priority < 0) ? defaultprio : priority;
}

// Add a BEV vector for a given pnp compatible option rom.
void
boot_add_bev(u16 seg, u16 bev, u16 desc, int prio)
{
    bootentry_add(IPL_TYPE_BEV, defPrio(prio, DefaultBEVPrio)
                  , SEGOFF(seg, bev).segoff
                  , desc ? MAKE_FLATPTR(seg, desc) : "Unknown");
    DefaultBEVPrio = DEFAULT_PRIO;
}

// Add a bcv entry for an expansion card harddrive or legacy option rom
void
boot_add_bcv(u16 seg, u16 ip, u16 desc, int prio)
{
    bootentry_add(IPL_TYPE_BCV, defPrio(prio, DefaultHDPrio)
                  , SEGOFF(seg, ip).segoff
                  , desc ? MAKE_FLATPTR(seg, desc) : "Legacy option rom");
}

void
boot_add_floppy(struct drive_s *drive_g, const char *desc, int prio)
{
    bootentry_add(IPL_TYPE_FLOPPY, defPrio(prio, DefaultFloppyPrio)
                  , (u32)drive_g, desc);
}

void
boot_add_hd(struct drive_s *drive_g, const char *desc, int prio)
{
    bootentry_add(IPL_TYPE_HARDDISK, defPrio(prio, DefaultHDPrio)
                  , (u32)drive_g, desc);
}

void
boot_add_cd(struct drive_s *drive_g, const char *desc, int prio)
{
    bootentry_add(IPL_TYPE_CDROM, defPrio(prio, DefaultCDPrio)
                  , (u32)drive_g, desc);
}

// Add a CBFS payload entry
void
boot_add_cbfs(void *data, const char *desc, int prio)
{
    bootentry_add(IPL_TYPE_CBFS, defPrio(prio, DEFAULT_PRIO), (u32)data, desc);
}


/****************************************************************
 * Keyboard calls
 ****************************************************************/

// See if a keystroke is pending in the keyboard buffer.
static int
check_for_keystroke(void)
{
    struct bregs br;
    memset(&br, 0, sizeof(br));
    br.flags = F_IF|F_ZF;
    br.ah = 1;
    call16_int(0x16, &br);
    return !(br.flags & F_ZF);
}

// Return a keystroke - waiting forever if necessary.
static int
get_raw_keystroke(void)
{
    struct bregs br;
    memset(&br, 0, sizeof(br));
    br.flags = F_IF;
    call16_int(0x16, &br);
    return br.ah;
}

// Read a keystroke - waiting up to 'msec' milliseconds.
static int
get_keystroke(int msec)
{
    u32 end = irqtimer_calc(msec);
    for (;;) {
        if (check_for_keystroke())
            return get_raw_keystroke();
        if (irqtimer_check(end))
            return -1;
        yield_toirq();
    }
}


/****************************************************************
 * Boot menu and BCV execution
 ****************************************************************/

#define DEFAULT_BOOTMENU_WAIT 2500

// Show IPL option menu.
void
interactive_bootmenu(void)
{
    // XXX - show available drives?

    if (! CONFIG_BOOTMENU || !romfile_loadint("etc/show-boot-menu", 1))
        return;

    while (get_keystroke(0) >= 0)
        ;

    char *bootmsg = romfile_loadfile("etc/boot-menu-message", NULL);
    int menukey = romfile_loadint("etc/boot-menu-key", 0x86);
    printf("%s", bootmsg ?: "\nPress F12 for boot menu.\n\n");
    free(bootmsg);

    u32 menutime = romfile_loadint("etc/boot-menu-wait", DEFAULT_BOOTMENU_WAIT);
    enable_bootsplash();
    int scan_code = get_keystroke(menutime);
    disable_bootsplash();
    if (scan_code != menukey)
        return;

    while (get_keystroke(0) >= 0)
        ;

    printf("Select boot device:\n\n");
    wait_threads();

    // Show menu items
    int maxmenu = 0;
    struct bootentry_s *pos;
    hlist_for_each_entry(pos, &BootList, node) {
        char desc[60];
        maxmenu++;
        printf("%d. %s\n", maxmenu
               , strtcpy(desc, pos->description, ARRAY_SIZE(desc)));
    }

    // Get key press
    for (;;) {
        scan_code = get_keystroke(1000);
        if (scan_code >= 1 && scan_code <= maxmenu+1)
            break;
    }
    printf("\n");
    if (scan_code == 0x01)
        // ESC
        return;

    // Find entry and make top priority.
    int choice = scan_code - 1;
    hlist_for_each_entry(pos, &BootList, node) {
        if (! --choice)
            break;
    }
    hlist_del(&pos->node);
    pos->priority = 0;
    hlist_add_head(&pos->node, &BootList);
}

// BEV (Boot Execution Vector) list
struct bev_s {
    int type;
    u32 vector;
};
static struct bev_s BEV[20];
static int BEVCount;
static int HaveHDBoot, HaveFDBoot;

static void
add_bev(int type, u32 vector)
{
    if (type == IPL_TYPE_HARDDISK && HaveHDBoot++)
        return;
    if (type == IPL_TYPE_FLOPPY && HaveFDBoot++)
        return;
    if (BEVCount >= ARRAY_SIZE(BEV))
        return;
    struct bev_s *bev = &BEV[BEVCount++];
    bev->type = type;
    bev->vector = vector;
}

// Prepare for boot - show menu and run bcvs.
void
bcv_prepboot(void)
{
    if (! CONFIG_BOOT)
        return;

    int haltprio = find_prio("HALT");
    if (haltprio >= 0)
        bootentry_add(IPL_TYPE_HALT, haltprio, 0, "HALT");

    // Map drives and populate BEV list
    struct bootentry_s *pos;
    hlist_for_each_entry(pos, &BootList, node) {
        switch (pos->type) {
        case IPL_TYPE_BCV:
            call_bcv(pos->vector.seg, pos->vector.offset);
            add_bev(IPL_TYPE_HARDDISK, 0);
            break;
        case IPL_TYPE_FLOPPY:
            map_floppy_drive(pos->drive);
            add_bev(IPL_TYPE_FLOPPY, 0);
            break;
        case IPL_TYPE_HARDDISK:
            map_hd_drive(pos->drive);
            add_bev(IPL_TYPE_HARDDISK, 0);
            break;
        case IPL_TYPE_CDROM:
            map_cd_drive(pos->drive);
            // NO BREAK
        default:
            add_bev(pos->type, pos->data);
            break;
        }
    }

    // If nothing added a floppy/hd boot - add it manually.
    add_bev(IPL_TYPE_FLOPPY, 0);
    add_bev(IPL_TYPE_HARDDISK, 0);
}


/****************************************************************
 * Boot code (int 18/19)
 ****************************************************************/

// Jump to a bootup entry point.
static void
call_boot_entry(struct segoff_s bootsegip, u8 bootdrv)
{
    dprintf(1, "Booting from %04x:%04x\n", bootsegip.seg, bootsegip.offset);
    struct bregs br;
    memset(&br, 0, sizeof(br));
    br.flags = F_IF;
    br.code = bootsegip;
    // Set the magic number in ax and the boot drive in dl.
    br.dl = bootdrv;
    br.ax = 0xaa55;
    farcall16(&br);
}

// Boot from a disk (either floppy or harddrive)
static void
boot_disk(u8 bootdrv, int checksig)
{
    u16 bootseg = 0x07c0;

    // Read sector
    struct bregs br;
    memset(&br, 0, sizeof(br));
    br.flags = F_IF;
    br.dl = bootdrv;
    br.es = bootseg;
    br.ah = 2;
    br.al = 1;
    br.cl = 1;
    call16_int(0x13, &br);

    if (br.flags & F_CF) {
        printf("Boot failed: could not read the boot disk\n\n");
        return;
    }

    if (checksig) {
        struct mbr_s *mbr = (void*)0;
        if (GET_FARVAR(bootseg, mbr->signature) != MBR_SIGNATURE) {
            printf("Boot failed: not a bootable disk\n\n");
            return;
        }
    }

    /* Canonicalize bootseg:bootip */
    u16 bootip = (bootseg & 0x0fff) << 4;
    bootseg &= 0xf000;

    call_boot_entry(SEGOFF(bootseg, bootip), bootdrv);
}

// Boot from a CD-ROM
static void
boot_cdrom(struct drive_s *drive_g)
{
    if (! CONFIG_CDROM_BOOT)
        return;
    printf("Booting from DVD/CD...\n");

    int status = cdrom_boot(drive_g);
    if (status) {
        printf("Boot failed: Could not read from CDROM (code %04x)\n", status);
        return;
    }

    u8 bootdrv = CDEmu.emulated_drive;
    u16 bootseg = CDEmu.load_segment;
    /* Canonicalize bootseg:bootip */
    u16 bootip = (bootseg & 0x0fff) << 4;
    bootseg &= 0xf000;

    call_boot_entry(SEGOFF(bootseg, bootip), bootdrv);
}

// Boot from a CBFS payload
static void
boot_cbfs(struct cbfs_file *file)
{
    if (!CONFIG_COREBOOT_FLASH)
        return;
    printf("Booting from CBFS...\n");
    cbfs_run_payload(file);
}

// Boot from a BEV entry on an optionrom.
static void
boot_rom(u32 vector)
{
    printf("Booting from ROM...\n");
    struct segoff_s so;
    so.segoff = vector;
    call_boot_entry(so, 0);
}

// Unable to find bootable device - warn user and eventually retry.
static void
boot_fail(void)
{
    if (BootRetryTime == (u32)-1)
        printf("No bootable device.\n");
    else
        printf("No bootable device.  Retrying in %d seconds.\n"
               , BootRetryTime/1000);
    // Wait for 'BootRetryTime' milliseconds and then reboot.
    u32 end = irqtimer_calc(BootRetryTime);
    for (;;) {
        if (BootRetryTime != (u32)-1 && irqtimer_check(end))
            break;
        yield_toirq();
    }
    printf("Rebooting.\n");
    reset();
}

// Determine next boot method and attempt a boot using it.
static void
do_boot(int seq_nr)
{
    if (! CONFIG_BOOT)
        panic("Boot support not compiled in.\n");

    if (seq_nr >= BEVCount)
        boot_fail();

    // Boot the given BEV type.
    struct bev_s *ie = &BEV[seq_nr];
    switch (ie->type) {
    case IPL_TYPE_FLOPPY:
        printf("Booting from Floppy...\n");
        boot_disk(0x00, CheckFloppySig);
        break;
    case IPL_TYPE_HARDDISK:
        printf("Booting from Hard Disk...\n");
        boot_disk(0x80, 1);
        break;
    case IPL_TYPE_CDROM:
        boot_cdrom((void*)ie->vector);
        break;
    case IPL_TYPE_CBFS:
        boot_cbfs((void*)ie->vector);
        break;
    case IPL_TYPE_BEV:
        boot_rom(ie->vector);
        break;
    case IPL_TYPE_HALT:
        boot_fail();
        break;
    }

    // Boot failed: invoke the boot recovery function
    struct bregs br;
    memset(&br, 0, sizeof(br));
    br.flags = F_IF;
    call16_int(0x18, &br);
}

int BootSequence VARLOW = -1;

// Boot Failure recovery: try the next device.
void VISIBLE32FLAT
handle_18(void)
{
    debug_enter(NULL, DEBUG_HDL_18);
    int seq = BootSequence + 1;
    BootSequence = seq;
    do_boot(seq);
}

// INT 19h Boot Load Service Entry Point
void VISIBLE32FLAT
handle_19(void)
{
    debug_enter(NULL, DEBUG_HDL_19);
    BootSequence = 0;
    do_boot(0);
}