btrfs-progs: Add minimum device size check

btrfs-progs: Add minimum device size check

Btrfs has global block reservation, so even mkfs.btrfs can execute
without problem, there is still a possibility that the filesystem can't
be mounted.
For example when mkfs.btrfs on a 8M file on x86_64 platform, kernel will
refuse to mount due to ENOSPC, since system block group takes 4M and
mixed block group takes 4M, and global block reservation will takes all
the 4M from mixed block group, which makes btrfs unable to create uuid
tree.

This patch will add minimum device size check before actually mkfs.
The minimum size calculation uses a simplified one:
minimum_size_for_each_dev = 2 * (system block group + global block rsv)
and global block rsv = leafsize << 10

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>