Re: How to debug 'out of disk' error.

["Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>]

On 16.03.2011 23:00, Lennart Sorensen wrote:
> On Wed, Mar 16, 2011 at 09:19:12PM +0100, Vladimir 'φ-coder/phcoder' Serbinenko wrote:
>   
>> Following may help:
>> === modified file 'grub-core/disk/i386/pc/biosdisk.c'
>> --- grub-core/disk/i386/pc/biosdisk.c    2011-01-04 14:42:47 +0000
>> +++ grub-core/disk/i386/pc/biosdisk.c    2011-03-16 20:17:57 +0000
>> @@ -80,6 +80,9 @@
>>    regs.flags = GRUB_CPU_INT_FLAGS_DEFAULT;
>>  
>>    grub_bios_interrupt (0x13, &regs);
>> +  if (!(regs.flags & GRUB_CPU_INT_FLAGS_CARRY))
>> +    return 0;
>> +
>>    return (regs.eax >> 8) & 0xff;
>>  }
>>     
> I now got this:
>
> GRUB loading.
> Welcome to GRUB!
>
> int13_ext fixup due to CARRY flag
> int13_ext fixup due to CARRY flag
> int13_ext fixup due to CARRY flag
> int13_ext fixup due to CARRY flag
> int13_ext fixup due to CARRY flag
> int13_ext fixup due to CARRY flag
> int13_ext fixup due to CARRY flag
> int13_ext fixup due to CARRY flag
> int13_ext fixup due to CARRY flag
>   
It's not really a fixup. Correct return on no error is CF=0 AH=0. Some
BIOSes in some other functions returned CF=0, AH!= 0 on no error so it
was a wild guess.
> Failed int13_ext call: ah=42, drive=80, dap=   6fe00 returned eax=8000
>   
Error 0x80 according to
http://www.delorie.com/djgpp/doc/rbinter/it/34/2.html means timeout.
Following code would retry on timeout:
=== modified file 'grub-core/disk/i386/pc/biosdisk.c'
--- grub-core/disk/i386/pc/biosdisk.c    2011-01-04 14:42:47 +0000
+++ grub-core/disk/i386/pc/biosdisk.c    2011-03-16 22:13:12 +0000
@@ -72,6 +72,8 @@
 grub_biosdisk_rw_int13_extensions (int ah, int drive, void *dap)
 {
   struct grub_bios_int_registers regs;
+  int tries = 4;
+ retry:
   regs.eax = ah << 8;
   /* compute the address of disk_address_packet */
   regs.ds = (((grub_addr_t) dap) & 0xffff0000) >> 4;
@@ -80,6 +82,16 @@
   regs.flags = GRUB_CPU_INT_FLAGS_DEFAULT;
 
   grub_bios_interrupt (0x13, &regs);
+  if (!(regs.flags & GRUB_CPU_INT_FLAGS_CARRY))
+    return 0;
+
+  if (((regs.eax >> 8) & 0xff) == 0x80 && tries)
+    {
+      grub_millisleep (10);
+      tries--;
+      goto retry;
+    }
+
   return (regs.eax >> 8) & 0xff;
 }
 

> error: hd0 out of disk.
> Entering rescue mode...
> grub rescue>
>
> I am now using 1.99-rc1.  Here is the biosdisk.c with my changes.
>
>   
>
>
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>   


-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko