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

[Vladimir 'φ-coder/phcoder' Serbinenko]

On 16.03.2011 21:09, Lennart Sorensen wrote:
> On Wed, Mar 16, 2011 at 03:23:58PM -0400, Lennart Sorensen wrote:
>   
>> On Wed, Mar 16, 2011 at 03:19:48PM -0400, Phillip Susi wrote:
>>     
>>> On 3/16/2011 1:32 PM, Lennart Sorensen wrote:
>>>       
>>>> So I now have some debug info:
>>>>
>>>> version=48
>>>> total_sectors=156312576 C=16383 H=16 S=63
>>>> error: hd0,msdos1 out of disk.
>>>> Entering rescue mode...
>>>> grub rescue>
>>>>
>>>> So version is returning something, and it is actually getting the disk
>>>> size properly.  I wonder what else could cause the out of disk message
>>>> then.
>>>>         
>>> What does the partition table look like?  It doesn't extend beyond
>>> sector 156312575 does it?
>>>
>>> Also I wonder about why H=16.  It should be 255.
>>>       
>> Well usually it should, but not always.
>>
>> Here is the partition table:
>>
>> Disk /dev/sda: 80.0 GB, 80032038912 bytes
>> 255 heads, 63 sectors/track, 9730 cylinders, total 156312576 sectors
>> Units = sectors of 1 * 512 = 512 bytes
>> Sector size (logical/physical): 512 bytes / 512 bytes
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>> Disk identifier: 0x0004a073
>>
>>    Device Boot      Start         End      Blocks   Id  System
>> /dev/sda1   *        2048   152350719    76174336   83  Linux
>> /dev/sda2       152352766   156311551     1979393    5  Extended
>> /dev/sda5       152352768   156311551     1979392   82  Linux swap / Solaris
>>     
> I have now determined that the call to grub_biosdisk_rw_int13_extensions
> fails here:
>
>         if (grub_biosdisk_rw_int13_extensions (cmd + 0x42, data->drive, dap))
>           {
>             /* Fall back to the CHS mode.  */
>             data->flags &= ~GRUB_BIOSDISK_FLAG_LBA;
>             disk->total_sectors = data->cylinders * data->heads * 
> data->sectors;
>             return grub_biosdisk_rw (cmd, disk, sector, size, segment);
>           }
>
> Then LBA gets disabled, and access beyond CHS range is gone, and the
> error about 'out of disk' happens.
>
>   
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;
 }
 


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

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