Re: booting btrfs

[Chris Murphy]

On Dec 21, 2013, at 12:18 AM, Andrey Borzenkov <address@hidden> wrote:
> 
> Do you need to reinvent the wheel?
> 
> /Boot-Environments
>  /Boot_Environment_1
>    /root
>    /boot
>    ...
>  /Boot_Environment_2
>    ...
> 
> The only thing you need to do to switch is equivalent of "btrfs
> set-default /Boot-Environments/Boot_Envirnment_2 …

I don't need to, but distros do reinvent wheels. If they will cooperate on the 
usage of set-default then sure, that's preferred. But historically they put 
next to no effort in preserving the bootability of a previously working distro 
install.

So I'd only be in favor of opening up the set-default can of worms if distros 
can agree on some parameters for multiboot on Btrfs and how to share the 
set-default state. Otherwise I feel like this becomes yet another way for them 
to step on each other.

As for grub's part in the solution, it seems like it would need to understand 
absolute paths to subvol 5, as well as relative paths to the default subvol 
(set with the 'btrfs subvol set-default' command). I think syntax wise it's 
simplest to use / for absolute and no-/ for relative to default. What do you 
think?

I still don't think it needs syntax of subvolids. 


> except it is
> not that straightforward in current btrfs because path names are
> resolved relative to current root :)

Navigation of a currently mounted subvolume, yes, I can only navigate below 
that point. It's no different than being in chroot, or mounting a partition and 
being unable to navigate into other partitions. 'btrfs subvol set-default' 
requires both <subvolid> and a <mountpoint>.


Chris Murphy