Re: [RFC][PATCH] Apple SMC driver (hardware monitoring and control)

[Nicolas Boichat <nicolas@boichat.ch>]

Hello,

Cong WANG wrote:
> 2007/3/14, Cong WANG wrote:
>> I am sorry. I forgot to CC to the list.
>>
>> 2007/3/14, Nicolas Boichat wrote:
>> > Hello,
>> >
>>
>> <snip>
>>
>> > +static ssize_t applesmc_show_fan_manual(struct device *dev, char *buf,
>> > +                                                               int
>> offset)
>> > +{
>> > +       int ret;
>> > +       u16 manual = 0;
>> > +       u8 buffer[2];
>> > +
>> > +       down(&applesmc_sem);
>> > +
>> > +       ret = applesmc_read_key(FANS_MANUAL, buffer, 2);
>> > +       manual = ((buffer[0] << 8 | buffer[1]) >> offset) & 0x01;
>> > +
>> > +       up(&applesmc_sem);
>> > +       if (ret)
>> > +               return ret;
>> > +       else
>> > +               return sprintf(buf, "%d\n", manual);
>> > +}
>> > +
>>
>> I doubt about your last 'sprintf'. Your 'buf' just has only two 'u8's,
>> which maybe only has two bytes, and '\n' already consumes one. So only
>> one byte is left for the decimal vaule of 'manual'. Even it is just
>> less than 10, just as what you want, the final '\0' is omitted!
>>
>> What's more, you can't get such information from the return value of
>> 'sprintf'. So I suggest you to choose 'snprintf' instead.
>>
> 
> Sorry. I thought his 'buffer' as 'buf'. But my suggestion is still
> worthy your thinking.

I'm quite sure using sprintf is ok. At least it's the way sysfs helper
functions are coded in other parts of the kernel too.

I agree that the variable names (buf and buffer) used are quite
confusing though... I'll fix that.

Best regards,

Nicolas