Read available data from a host device into a user-provided buffer
#include <qvm/cdev.h>
int cdev_input_receive(struct cdev_state *cds, void *dst, unsigned len)
Use this function if you are managing your own input and output buffers (see cdev_setup()). Calling this function makes sense only if you are NOT using the internal buffers (i.e., you specified a zero buffer size when calling cdev_setup()).
If successful, the number of characters read; otherwise, a negative errno value.