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Date: Wed, 11 Mar 2009 07:59:07 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
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To: Vitaly Mayatskikh <v.mayatskih@gmail.com>
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On Wed, 11 Mar 2009, Vitaly Mayatskikh wrote:
> 
> (v)scnprintf says it should return 0 when size is 0, but doesn't do
> so. Also size_t is unsigned, it can't be less then 0. Fix the code and
> comments.

That is bogus.

The code really does (od "did"? Maybe you removed it) check for _smaller_ 
than 0:

	int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
	{
		...
		/* Reject out-of-range values early.  Large positive sizes are
		   used for unknown buffer sizes. */
		if (unlikely((int) size < 0)) {
			/* There can be only one.. */
			static char warn = 1;
			WARN_ON(warn);
			warn = 0;
			return 0;
		}
		...

because under/overflows have happened.

The kernel is _not_ a regular libc. We have different rules.

		Linus