Re: [PATCH] btrfs: Fix no space bug caused by removing bg

From: David Sterba <dsterba@suse.cz>
To: "Hugo Mills" <hugo@carfax.org.uk>,
	dsterba@suse.cz,
	"Holger Hoffstätte" <holger.hoffstaette@googlemail.com>,
	linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] btrfs: Fix no space bug caused by removing bg
Date: Wed, 23 Sep 2015 15:12:26 +0200	[thread overview]
Message-ID: <20150923131226.GA12815@twin.jikos.cz> (raw)
In-Reply-To: <20150922143602.GI5918@carfax.org.uk>

On Tue, Sep 22, 2015 at 02:36:02PM +0000, Hugo Mills wrote:
> > Yeah, right now there's no persistent default for the allocator. I'm
> > still hoping that the object properties will magically solve that.
> 
>    There's no obvious place that filesystem-wide properties can be
> stored, though. There's a userspace tool to manipulate the few current
> FS-wide properties, but that's all special-cased to use the
> "historical" ioctls for those properties, with no generalisation of a
> property store, or even (IIRC) any external API for them.

>From the UI point, we proposed to add a specifier that would route the
property to either subvolume or the filesystem:

$ btrfs prop set -t filesystem bgtype raid0
$ btrfs prop set -t subvolume bgtype raid1

How this will get stored in the xattrs is another question. As there's
always only single instance of the filesystem properties, it coud be
something like 'btrfs.fs.bgtype' and be stored as a xattr of the
toplevel subvolume.