Man page 9 : input_get_new_minor

input_get_new_minor - allocates a new input minor number

int input_get_new_minor(int  legacy_base , unsigned int  legacy_num , bool  allow_dynamic );

legacy_base
    beginning or the legacy range to be searched

legacy_num
    size of legacy range

allow_dynamic
    whether we can also take ID from the dynamic range

This function allocates a new device minor for from input major namespace. Caller can request legacy minor by specifying legacy_base and legacy_num parameters and whether ID can be allocated from dynamic range if there are no free IDs in legacy range.