On Wed, Feb 24, 2021 at 10:27:45AM +0800, Anand Jain wrote:

On 23/02/2021 21:53, David Sterba wrote:

quoted

On Mon, Feb 22, 2021 at 10:19:06PM +0100, Goffredo Baroncelli wrote:

quoted

From: Goffredo Baroncelli <redacted>

This ioctl is a base for returning / setting information from / to  the
fields of the btrfs_dev_item object.

Please don't add a new ioctl for properties, they're using the xattr as
interface alrady.

IMO a feature like this can be in memory only initially[1]. And later
when this feature is stable, add its on-disk.

The "metadata_only" and "data_only" settings need to be persistent for
the feature to really work.

It is very expensive to recover (need to balance metadata on a spinning
disk) if the filesystem allocates a new chunk after mount but before
userspace can reestablish the preferences.  The whole point of
metadata_only and data_only is that we never have to do that.

[1] https://patchwork.kernel.org/project/linux-btrfs/patch/0ed770d6d5e37fc942f3034d917d2b38477d7d20.1613668002.git.anand.jain@oracle.com/


Thanks, Anand