[arch-general] BTRFS integration

[C Anthony Risinger]

On Wed, May 5, 2010 at 6:28 PM, Isaac Dupree
<ml at isaac.cedarswampstudios.org> wrote:
> On 05/05/10 19:10, C Anthony Risinger wrote:
>>
>> subvolumes can be mounted two ways via a mount option:
>>
>> 1) subvol=<subvolume_name>
>> 2) subvol=<subvolume_id>
>>
>> 1 can only be used if the subvolume is in the root of the FS, i.e.
>> /__active would work, but /root/__active would NOT... the mount option
>> cannot have slashes and i don't know if this will change.
>
> since we control the structure, why not the (slightly uglier)
>
> /root__active
> /root__rollback
> /root__20090807
> /home__active
> /home__...
>
> just remove the slashes or replace them with some other character like dash
> or underscore.  `ls` will still sort things alphabetically so there will
> still be some semblance of order for the humans, and it would behave nearly
> the same to the machine.  And it will be easier for debugging purposes if
> all these subvolumes are accessible by name.  (Do you think you can ask
> upstream whether they want to change or keep the restriction on slashes(i.e.
> volumes in subdirectories), in light of our '.' organizational ideas?)

ah, yeah thanks, i meant to mention that too but got lost in the
myriad of letters i had written :).

this would work just fine, and has the benefit of working on pretty
much any recent-ish kernel/btrfs version.  the end user should never
see any of this anyway.  iirc, this is how fedora does it (something
like yum_snapshot_20090807).  but fedora installs into the default "."
subvolume, so each time you take a snapshot you get a bunch of empty
folders from previous snapshots (the snapshot yum_snapshot_20090808
would have an empty folder yum_snapshot_20090807 [snapshots not
recursive]); we can stop this by not installing into the "." subvolume
and using an actual mount point for operations, plus it keep the real
root "device" (root__active) nice and clean.

as for upstream, they are pretty receptive to changes right now.  im
not sure if the slash thing is a limit of the mount command/something
else, or just was not implemented.  afiak, the <id> mounting was
implemented to replace the name mounting [and for setting a new
default], i'm not sure if <name> mounting will be dropped or not.
also even if they did implement, we prob wouldn't see it until 2.6.35
:(.

any other ideas besides rollbacks and an original snapshot that btrfs
could be used for?

C Anthony