strict_strtoull — convert a string to an unsigned long long strictly
int strict_strtoull ( | const char * | cp, |
| unsigned int | base, | |
| unsigned long long * | res); |
strict_strtoull converts a string to an unsigned long long only if the string is really an unsigned long long string, any string containing any invalid char at the tail will be rejected and -EINVAL is returned, only a newline char at the tail is acceptible because people generally
echo 1024 > /sys/module/e1000/parameters/copybreak
echo will append a newline to the tail of the string.
It returns 0 if conversion is successful and *res is set to the converted value, otherwise it returns -EINVAL and *res is set to 0.
simple_strtoull just ignores the successive invalid characters and return the converted value of prefix part of the string.