raw format warning

[yjqg6666]

$ qemu-system-x86_64 -fda OSASK-Linux/src/helloos.img
WARNING: Image format was not specified for 'OSASK-Linux/src/helloos.img' and probing guessed raw.
Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
Specify the 'raw' format explicitly to remove the restrictions.

ref: https://unix.stackexchange.com/questions/276480/booting-a-raw-disk-image-in-qemu

suggestion:
$ qemu-system-x86_64 -drive format=raw,file=OSASK-Linux/src/helloos.img