[PATCH] Support multiple hard disks in boot list.

[Gaurav Poothia]

If multiple disks in boot order and first is unbootable
then fallback to other disks in list.

Signed-off-by: Gaurav Poothia 
---
 src/block.c |  3 ++-
 src/block.h |  2 +-
 src/boot.c  | 30 +++++++++++++++++++-----------
 3 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/src/block.c b/src/block.c
index d104f6d..5c78533 100644
--- a/src/block.c
+++ b/src/block.c
@@ -238,7 +238,7 @@ add_drive(struct drive_s **idmap, u8 *count, struct drive_s *drive)
 }

// Map a hard drive
-void
+int
 map_hd_drive(struct drive_s *drive)
 {
     ASSERT32FLAT();
@@ -252,6 +252,7 @@ map_hd_drive(struct drive_s *drive)

// Fill "fdpt" structure.
     fill_fdpt(drive, hdid);
+    return hdid;
 }

// Map a cd
diff --git a/src/block.h b/src/block.h
index f03ec38..68f2f32 100644
--- a/src/block.h
+++ b/src/block.h
@@ -109,7 +109,7 @@ extern u8 *bounce_buf_fl;
 struct drive_s *getDrive(u8 exttype, u8 extdriveoffset);
 int getDriveId(u8 exttype, struct drive_s *drive);
 void map_floppy_drive(struct drive_s *drive);
-void map_hd_drive(struct drive_s *drive);
+int map_hd_drive(struct drive_s *drive);
 void map_cd_drive(struct drive_s *drive);
 struct int13dpt_s;
 int fill_edd(struct segoff_s edd, struct drive_s *drive_gf);
diff --git a/src/boot.c b/src/boot.c
index 59623fb..9b9cf91 100644
--- a/src/boot.c
+++ b/src/boot.c
@@ -527,16 +527,16 @@ interactive_bootmenu(void)
 struct bev_s {
     int type;
     u32 vector;
+    // Applicable to hard disks only
+    int hdid;
 };
 static struct bev_s BEV[20];
 static int BEVCount;
 static int HaveHDBoot, HaveFDBoot;

static void
-add_bev(int type, u32 vector)
+add_bev(int type, u32 vector, int hdid)
 {
-    if (type == IPL_TYPE_HARDDISK && HaveHDBoot++)
-        return;
     if (type == IPL_TYPE_FLOPPY && HaveFDBoot++)
         return;
     if (BEVCount >= ARRAY_SIZE(BEV))
@@ -544,12 +544,15 @@ add_bev(int type, u32 vector)
     struct bev_s *bev = &BEV[BEVCount++];
     bev->type = type;
     bev->vector = vector;
+    bev->hdid = hdid;
 }

+
 // Prepare for boot - show menu and run bcvs.
 void
 bcv_prepboot(void)
 {
+    int hdid = -1;
     if (! CONFIG_BOOT)
         return;

@@ -563,28 +566,30 @@ bcv_prepboot(void)
         switch (pos->type) {
         case IPL_TYPE_BCV:
             call_bcv(pos->vector.seg, pos->vector.offset);
-            add_bev(IPL_TYPE_HARDDISK, 0);
+            add_bev(IPL_TYPE_HARDDISK, 0, -1);
             break;
         case IPL_TYPE_FLOPPY:
             map_floppy_drive(pos->drive);
-            add_bev(IPL_TYPE_FLOPPY, 0);
+            add_bev(IPL_TYPE_FLOPPY, 0, -1);
             break;
         case IPL_TYPE_HARDDISK:
-            map_hd_drive(pos->drive);
-            add_bev(IPL_TYPE_HARDDISK, 0);
+            hdid = map_hd_drive(pos->drive);
+            add_bev(IPL_TYPE_HARDDISK, 0, hdid);
+            HaveHDBoot++;
             break;
         case IPL_TYPE_CDROM:
             map_cd_drive(pos->drive);
             // NO BREAK
         default:
-            add_bev(pos->type, pos->data);
+            add_bev(pos->type, pos->data, -1);
             break;
         }
     }

// If nothing added a floppy/hd boot - add it manually.
-    add_bev(IPL_TYPE_FLOPPY, 0);
-    add_bev(IPL_TYPE_HARDDISK, 0);
+    add_bev(IPL_TYPE_FLOPPY, 0, -1);
+    if (HaveHDBoot == 0)
+      add_bev(IPL_TYPE_HARDDISK, 0, -1);
 }

@@ -731,7 +736,10 @@ do_boot(int seq_nr)
         break;
     case IPL_TYPE_HARDDISK:
         printf("Booting from Hard Disk...\n");
-        boot_disk(0x80, 1);
+        if (ie->hdid == -1)
+          boot_disk(0x80 , 1);
+        else
+          boot_disk(0x80 + ie->hdid, 1);
         break;
     case IPL_TYPE_CDROM:
         boot_cdrom((void*)ie->vector);

[Kevin O'Connor]

On Fri, Jun 30, 2017 at 08:48:27PM -0400, Gaurav Poothia wrote:
> If multiple disks in boot order and first is unbootable
> then fallback to other disks in list.

[...]
> @@ -731,7 +736,10 @@ do_boot(int seq_nr)
>          break;
>      case IPL_TYPE_HARDDISK:
>          printf("Booting from Hard Disk...\n");
>    boot_disk(0x80, 1);
>    if (ie->hdid == -1)
>      boot_disk(0x80 , 1);
>    else
>      boot_disk(0x80 + ie->hdid, 1);
>    break;
> case IPL_TYPE_CDROM:
>        boot_cdrom((void*)ie->vector);

Ultimately, what this patch does is set the DL register to something
other than 0x80.  I tested this approach a few years ago, and at the
time I could not find a single bootloader that used DL.  What
bootloaders did you test with this, and which ones worked and did not
work?

-Kevin

[Gaurav Poothia]

Hi Kevin,
Thanks for your response!

I have tested this successfully against grub (specifically GRUB 2)
Since you asked I went digging for the relevant code in grub - here is
the line of code that will validate range of acceptable DL values and
if acceptable jump ahead to boot from that disk and skip hardcoding DL
to 0x80:
https://github.com/coreos/grub/blob/master/grub-core/boot/i386/pc/boot.S#L22...

So for example if bios were to set DL to 0x81 (by fallback logic in
the patch) that will be acceptable to grub

On Fri, Jul 7, 2017 at 7:55 AM, Kevin O'Connor  wrote:
> On Fri, Jun 30, 2017 at 08:48:27PM -0400, Gaurav Poothia wrote:
> > If multiple disks in boot order and first is unbootable
> > then fallback to other disks in list.
>
> [...]
> > @@ -731,7 +736,10 @@ do_boot(int seq_nr)
> >          break;
> >      case IPL_TYPE_HARDDISK:
> >          printf("Booting from Hard Disk...\n");
> >    boot_disk(0x80, 1);
> >    if (ie->hdid == -1)
> >      boot_disk(0x80 , 1);
> >    else
> >      boot_disk(0x80 + ie->hdid, 1);
> >    break;
> > case IPL_TYPE_CDROM:
> >        boot_cdrom((void*)ie->vector);
>
> Ultimately, what this patch does is set the DL register to something
> other than 0x80.  I tested this approach a few years ago, and at the
> time I could not find a single bootloader that used DL.  What
> bootloaders did you test with this, and which ones worked and did not
> work?
>
> -Kevin