just want to read the image or write access if you want to modify the
image).
-This is equivalent to the qemu parameter C<-drive file=filename,cache=off>.
+This is equivalent to the qemu parameter
+C<-drive file=filename,cache=off,if=virtio>.
Note that this call checks for the existence of C<filename>. This
stops you from specifying other types of drive which are supported
changes to be committed, although qemu can support this.
This is equivalent to the qemu parameter
-C<-drive file=filename,snapshot=on>.
+C<-drive file=filename,snapshot=on,if=virtio>.
Note that this call checks for the existence of C<filename>. This
stops you from specifying other types of drive which are supported
C<002> which creates new files with permissions like
"-rw-rw-r--" or "-rwxrwxr-x".
+The default umask is C<022>. This is important because it
+means that directories and device nodes will be created with
+C<0644> or C<0755> mode even if you specify C<0777>.
+
See also L<umask(2)>, C<$h-E<gt>mknod>, C<$h-E<gt>mkdir>.
This call returns the previous umask.