Re: booting btrfs

[Michael Chang]

2013/12/20 Vladimir 'φ-coder/phcoder' Serbinenko <address@hidden>:
> On 19.12.2013 17:13, Andrey Borzenkov wrote:
>> В Mon, 28 Oct 2013 01:44:26 +0100
>> Vladimir 'φ-coder/phcoder' Serbinenko <address@hidden> пишет:
>>
>>> I changed in trunk to make / refer to real root and modified
>>> grub-mkrelpath to follow the same convention, even if disk is mounted
>>> with subvolid.
>>>
>>
>> Can it cause compatibility issues? It means if config file that works
>> for grub before this change will stop working after. So e.g. attempt to
>> "configfile /file/from/partition/with/old/grub-mkconfig" will fail.
>>
> Normally I'd consider this a problem but the current behaviour is the
> intended one, just back when the code was written thre were no changing
> default yes
>> May be subvolume support should use different syntax. Something like
>>
>> (hd0,1){sv=subvolume}/xxx
>> (hd0,1){svid=NNN}/yyy
>>
> This would complicate the code a lot and commit us to maintaining it
> long-term. Given that btrfs isn't clasified as stable, I consider this
> behaviour change acceptable and it's better to handle this now rather
> than perpetuating the issue.

Please consider the case if a snapshot was taken against real root fs
tree to a subvolume with SNAPSHOT_ID. With syntax above providing
mount option support we can possibly boot that snapshot with this
config.

  set root=(hd0,1){svid=<SNAPSHOT_ID>}
  set prefix=($root)/boot/grub2
  normal

Without the syntax support it's almost impossible to do that. At lease
I can't figure out any.

Besides we may leverage that mount option support in grub-mount to
test/develop and so on. For modern innovative file systems the mount
option support is becoming necessary for dealing many different use
cases.

Thanks,
Michael

>> And continue to interpret old syntax as relative to default.
>>
>>
>>
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