[Mageia-dev] Grub2 vs. Grub Legacy in M3

Tue Jan 29 00:44:45 CET 2013

On 28/01/13 20:09, Frank Griffin wrote:
+
+>>
+>> ...this is where we disagree slightly ;)
+>> Chainloading into grub2 is not the best way, due to the block lists
+>> problem people keep mentioning and complaining about.
+>
+> Could you please explain why ?  The whole MBR/PBR design was set up so
+> that whatever gets loaded and receives control doesn't know which way it
+> happened.  How does grub2 break this ?
+>
+My limited understanding is that the code in the 512 byte PBR has to use 
+block lists to find the core image in /boot, since it is too small to 
+understand filesystems. This is fragile in that filesystems and file 
+utilities may move files around on disk invalidating the block lists, 
+and for this reason the method is discouraged.
+
+A far as I know the same potential problem exists with grub legacy.
+
+Whether the same fragility applies to the multiboot approach I am not 
+sure, as documentation is sparse, however grub2 developers agree that it 
+is a valid method.
+
+>> Chanloading is un-necessary
+>
+> I don't claim that it's necessary, just that it's more desirable than
+> requiring the MBR code to go poking around in partitons other than the
+> one from which it was installed.  If you're interested in keeping
+> partitions functionally as separate as they can be, it just makes sense
+> to have them booted by their own bootloaders.
+>
+
+The MBR code cannot go poking around. It points to one location only. In 
+the case of grub2 this is normally a copy of core.img located in the 
+'MBR-gap' of around 31kB (or larger depending on partitioning) below the 
+start of the first sector. This then launches the boot menu for the 
+system that created it, or a dedicated grub installation.
+
+If the intention is to put the bootloader in the root partition by 
+whatever method, then it has no relation to the MBR. The intention is to 
+boot into the system's bootloader from another primary bootloader.
+
+The bootloader built into the core.img in the system root *is* it's own, 
+just as would be the case with chainloading, so I don't really see the 
+distinction.
+
+Barry
+
+