On Mon, Jan 31, 2022 at 12:30:33PM +0200, Andy Shevchenko wrote:
> On Mon, Jan 31, 2022 at 12:25:09PM +0200, Andy Shevchenko wrote:
> > On Sun, Jan 30, 2022 at 12:49:37PM -0800, David Rientjes wrote:
> > > On Sat, 29 Jan 2022, Waiman Long wrote:
> > >
> > > > For *scnprintf(), vsnprintf() is always called even if the input size is
> > > > 0. That is a waste of time, so just return 0 in this case.
> >
> > Why do you think it's not legit?
>
> I have to elaborate.
>
> For *nprintf() the size=0 is quite useful to have.
> For *cnprintf() the size=0 makes less sense, but, if we read `man snprintf()`:
>
> The functions snprintf() and vsnprintf() do not write more than size bytes
> (including the terminating null byte ('\0')). If the output was truncated due
> to this limit, then the return value is the number of characters (excluding
> the terminating null byte) which would have been written to the final string
> if enough space had been available. Thus, a return value of size or more
> means that the output was truncated. (See also below under NOTES.)
>
> If an output error is encountered, a negative value is returned.
>
> Note the last sentence there. You need to answer to it in the commit message
> why your change is okay and it will show that you thought through all possible
> scenarios.
Also it seems currently the kernel documentation is not aligned with the code
"If @size is == 0 the function returns 0."
It should mention the (theoretical?) possibility of getting negative value,
if vsnprintf() returns negative value.
--
With Best Regards,
Andy Shevchenko
