[libvirt-users] virsh command 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? And at this point do we have method to access the data upload to the volume from vm? Thanks Bests Kimi Li