Linux swap file and LUKS

[Artem S. Tashkinov]

Hello,

The man-page of swapon says:

    The swap file implementation in the kernel expects to be able to 
write to the file directly, without the assistance of the filesystem.

Does that mean that if the user has a LUKS volume with a partition on 
it, in the end the swapfile on this partition will end up unecrypted?

Could someone please explain it in more details?

Regards,
Artem