fsx: add support for keeping existing file

With fsx -k, do not truncate existing file and use its size as upper
bound on file size.

This is needed to prevent fsx from truncating the file on start of
test when testing fsx on cloned files.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
1 file changed