Re: Replacing the legacy "map" command

[Pavel Roskin]

Quoting Javier Martín <address@hidden>:

> Then "drivemap" it is. I've already been delving into the depths of The
> Source, though I'd have preferred it to be commented a bit more
> exhaustively. Some times it's difficult to guess which methods to call,
> and it took me a bit to realize that I had to check with the disk
> "device" to see if it was a BIOS drive. Seems I had the wrong conception
> of what the disk "device" should be.

I suggest a simple approach starting from what can be done.  There  
will be a small resident piece of code installed to intercept  
interrupt 0x13 and replace the driver number according to the map.  We  
should keep that code simple.

The resident code should go through the list of the mapped drives, and  
if there is an entry in the table, replace the drive number.  That's  
two bytes for an entry.

I think the user interface should operate directly on that  
unidirectional map rather that with some complex swap rules that are  
translated to the map.  Sure, it won't be nice if some device is seen  
as two devices, especially if the OS uses BIOS.  But GRUB cannot  
prevent all stupid actions by users.

> By the way, floppies are usually also "BIOS drives". Should the command
> filter them out as sources for mapping? I think so, because OS loaders
> usually have different code for reading floppies and HDs. Concretely,
> floppy code usually makes some assumptions about drive geometry, uses
> only old CHS-like interfaces, and some things more I cannot remember
> now... it's been long since I wrote anything distantly similar to a
> bootloader.

We may still want to map a hard drive as a floppy.  I can imagine that  
some floppy readers may be seen as hard drives by the BIOS.

I think it's not the most important thing at the moment.  If there is  
a substantial risk of data corruption due to floppy-to-hdd remapping  
or duplicate drives, we can introduce extra safety checks.

--
Regards,
Pavel Roskin