Re: Future of installing GRUB to LVM volumes (and loop devices)

[Sebastian Pipping]

On 05/12/2015 01:41 PM, Andrei Borzenkov wrote:
> That's what mean - this is direct parent-child. But consider
> 
> address@hidden:~/build/grub> echo 0 2048 linear /dev/loop0 0 | sudo dmsetup 
> create whole
> address@hidden:~/build/grub> echo 0 59392 linear /dev/loop0 2048 | sudo 
> dmsetup create part
> 
> At this point /dev/mapper/part refers to partition of /dev/mapper/whole
> but there is not direct relationships between two that you can
> easily discover
> 
> address@hidden:~/build/grub> sudo dmsetup ls --tree
> whole (254:5)
>  └─ (7:0)
> part (254:6)
>  └─ (7:0)
> 
> and
> 
> address@hidden:~/build/grub> sudo ./grub-probe  -t hints_string -m device.map 
> /mnt 
> ./grub-probe: warning: unknown device type loop0
> .
> 
> address@hidden:~/build/grub> cat device.map 
> (hd0) /dev/mapper/whole
> 
> but
> 
> address@hidden:~/build/grub> sudo ./grub-probe  -t hints_string -m device.map 
> /mnt 
> ./grub-probe: warning: unknown device type loop0
> .
> --hint='hd0,msdos1' 
> address@hidden:~/build/grub> cat device.map
> (hd0) /dev/loop0
> 
> So in common cases it will work and is better as nothing, but there will be 
> corner cases that may fail.

Thanks for that explanation.

I understand that some relations may be hard to impossible to detect.
The cases that I have are plain parent-child relations, though.
It would rock the house to get these cases covered again.

(On a side note, text "unknown device type loop0" looks like a bug to me
since "loop0" is not a type.)


>>> Half working solution would be to assume that it is always child map.
>>>
>>> Or you can take shortcut and assume that /dev/mapper/XXXXpY is
>>> partition of /dev/mapper/XXX but you still will need to verify it.
>>>
>>> Patches are welcome.
>>
>> I am still wondering: how come it was working in GRUB 2.00 but now
>> longer is?
>>
> 
> But by you said in previous message that HEAD works? Not sure how
> though :)

That referred to the '(hd0)'-parameter-with-device-map case, only.

This patch to grml-debootstrap says best what has stopped working:
https://github.com/hartwork/grml-debootstrap/commit/a705ff45c2d053b0d90ec51700e2d25a760106f3

Best,



Sebastian