Re: [PATCH] Create floppy emulation boot CD with grub-mkimage

[Christian Franke <Christian.Franke@t-online.de>]

Robert Millan wrote:
> On Fri, Feb 15, 2008 at 11:32:49PM +0100, Christian Franke wrote:
>   
>>> I don't think it is really practical to support USB drives in 
>>> grub-mkrescue.
>>> You'd have to require root permissions, which IMO beats the point of having
>>> a separate script from grub-install in first place.
>>>       
>> It may be useful to create small rescue images which can be later put on 
>> USB key with dd.
>> (BTW: The "floppy" image actually boots from USB at least on one of my 
>> PC. It appears as hd0).
>>     
>
> Yes, but how different would those be from floppy output?  As you point out,
> floppy images work as well.
>
>   

For a BIOS which handles USB flash drives like USB hard drives, a valid 
hard disk boot sector with a partition table should be present.
With the floppy image, GRUB detects bogus partitions on (hd0), because 
boot.img contains the "floppy_probe" code in the partition table space. 
The boot sector is also not properly patched for hdd (need to replace 
jmp by nop at "boot_drive_check").

But it actually works without any change.


> Besides, dd'ing a grub image to that stick would render the rest of the device
> useless for filesystem data.
>
>   

Yes. But if you need a rescue boot device when floppy or CD cannot be 
used for some reason, you probably do not care about this :-)

It may be possible to produce a rescue image with a valid partition 
table such that a filesystem partition can be added later.

Otherwise, grub-setup/install may work to install grub on an USB flash 
drive which has partition table and filesystem.


>> The patch also adds a --joliet option, useful to access the long file 
>> names on Windows (which has no RR support).
>>     
>
> Is there any drawback in using --joliet ?  If not, I think it's better to do
> it by default to avoid "option creep".
>
>   

I'm not aware of any drawback.

Christian