(no subject)

[Vitaly Mayatskikh]

Forgot to sign-off...

(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.

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 0fbd012..8e75c7e 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -947,7 +947,7 @@ EXPORT_SYMBOL(vsnprintf);
  * @args: Arguments for the format string
  *
  * The return value is the number of characters which have been written into
- * the @buf not including the trailing '\0'. If @size is <= 0 the function
+ * the @buf not including the trailing '\0'. If @size is == 0 the function
  * returns 0.
  *
  * Call this function if you are already dealing with a va_list.
@@ -958,7 +958,8 @@ EXPORT_SYMBOL(vsnprintf);
 int vscnprintf(char *buf, size_t size, const char *fmt, va_list args)
 {
        int i;
-
+       if (!size)
+               return 0;
        i=vsnprintf(buf,size,fmt,args);
        return (i >= size) ? (size - 1) : i;
 }
@@ -998,7 +999,7 @@ EXPORT_SYMBOL(snprintf);
  * @...: Arguments for the format string
  *
  * The return value is the number of characters written into @buf not including
- * the trailing '\0'. If @size is <= 0 the function returns 0.
+ * the trailing '\0'. If @size is == 0 the function returns 0.
  */
 
 int scnprintf(char * buf, size_t size, const char *fmt, ...)
@@ -1006,6 +1007,8 @@ int scnprintf(char * buf, size_t size, const char *fmt, ...)
        va_list args;
        int i;
 
+       if (!size)
+               return 0;
        va_start(args, fmt);
        i = vsnprintf(buf, size, fmt, args);
        va_end(args);

-- 
wbr, Vitaly

Re: your mail

[Linus Torvalds]

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

Re: your mail

[Vitaly Mayatskikh]

> 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:

Well, (v)scnprintf says it returns 0 for size <= 0, but really returns
-1 for size == 0. I think, this code can't return 0 for size == 0:

	i=vsnprintf(buf,size,fmt,args);
	return (i >= size) ? (size - 1) : i;

Systemtap's script:

function test:long()
%{
        char tmp[256];
        long err;
        err = scnprintf(tmp, 0, "%lu", (long)128);
        THIS->__retvalue = err;
%}

probe begin
{
        printf("scnprintf returns %d\n", test());
}

stap -g scnprintf.stp
scnprintf returns -1

-- 
wbr, Vitaly