Questions about how block devices use snapshots

[Zhiyong Ye]

Dear all,

Qemu provides powerful snapshot capabilities for different file formats. 
But this is limited to the block backend being a file, and support is 
not good enough when it is a block device. When creating snapshots based 
on files, there is no need to specify the size of the snapshot image, 
which can grow dynamically as the virtual machine is used. But block 
devices are fixed in size at creation and cannot be dynamically grown at 
a later time.

So is there any way to support snapshots when the block backend is a 
block device?

Regards

Zhiyong