Initialize RAM from a file and save it to the file

[Hiroko Shimizu]

Hello, 

I'd like to initialize RAM from a specific file when RAM is created.
Then,  I tried using memory_region_init_ram_from_file(). 
I wonder what file format is necessary. I tried using a binary file, however the contents of the file wasn't recognized and file_size(defined in qemu_ram_alloc_from_fd()) was zero. 

Could you tell me what I need to do or another way to initialize RAM from a file?

Also, is it possible to save RAM's value to the file when a value is written to RAM which is initialized memory_region_init_ram_from_file()?

Best regard,

Hiroko