[libvirt] virsh vol-upload purpose question

I use virsh vol-upload to upload some data in a volume and use vol-download to download these data from the same volume, both these two commands work well. However, when I first use these two commands, I thought I can use vol-upload to upload some file, then attach this volume to a vm, and access the upload file in this vm. I did this experiment, bud it not success. Once I upload a file into a volume, attach it to a vm, then the vm can not recognize the file type of this vm, if I mkfs to the volume, the file I upload disappear. So, my question is the purpose of the vol-upload is just to save some data in the volume outside vm? I think it is more reasonable if we can access upload data from vm. Best Regards Kimi Li