linux-imx

btrfs: move and export can_overcommit

This is the first piece of moving the space reservation code to
space-info.c

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>