Make `btrfs filesystem mkswapfile` check if underlying filesystem has single DATA profile

[yarikoptic]

ATM command might succeed but then subsequent swapon would fail. Might be worth doing a check and issuing at least a warning ?

[kdave]

Yes that makes sense, the information is accessible from sysfs and not restricted. Alternatively the SEARCH_TREE ioctl can be used for that and read more information or do validation of the extents of the swapfile (e.g. the NODATASUM flag).

[marcosps]

Just sent a patch addressing this issue: https://lore.kernel.org/linux-btrfs/[email protected]/T/#u