Docker toolbox and virtualbox on windows. Permissions and Invalid Protocol error

I am trying to use a local volume for a container running a MySql server instance. I am launching the container with the command

$ -v /c/Users/my_data_dir:/var/lib/mysql

But I get an error saying that the directory must be writeble. But I am not able to do ‘chmod’ on my windows host using docker quickstart shell because I get ‘permission denied’

When I do:
$ ls -ld /c/Users/my_data_dir

from my windows host I get an output like:
drwxr-xr-x 1 User1 197121 0 nov 9 11:11 mysql_volume

Instead inside my docker-machine I get :
drwxrwxrwx 1 docker staff 4096 Nov 7 07:44 mysql_volume

Inside VM my directory is owned by a different user. And inside my VM if a make a command like ‘mkdir’ inside the shared volume i get this error:

root@default:/c/Users# mkdir prova
mkdir: can’t create directory ‘prova’: Protocol error

I have no idea how to deal with that!