vsnprintf patch

When using the snprintf function from the kernel the length returned is not the length written:

len = snprintf(test,1,"BLA 1");

len is 5 although test is "B"

the patch below fixes the symptom, but I am not sure if this is the real solution for this problem.

@@ -455,7 +455,10 @@
        /* the trailing null byte doesn't count towards the total
        * ++str;
        */
-       return str-buf;
+       if (str-buf > size)
+               return size;
+       else
+               return str-buf;
 }
 
 /**

Adrian

For what problem? In the example above, 5 is correct return value.

7.19.6.5 The snprintf function

Synopsis

#include <stdio.h>

int snprintf(char * restrict s, size_t n, const char * restrict format, ...);

Description

The snprintf function is equivalent to fprintf, except that the output is written into an array (specified by argument s) rather than to a stream. If n is zero, nothing is written, and s may be a null pointer. Otherwise, output characters beyond the n-1st are discarded rather than being written to the array, and a null character is written at the end of the characters actually written into the array. If copying takes place between objects that overlap, the behavior is undefined.

Returns

The snprintf function returns the number of characters that would have been written had n been sufficiently large, not counting the terminating null character, or a negative value if an encoding error occurred. Thus, the null-terminated output has been completely written if and only if the returned value is nonnegative and less than n.

This is how the function is defined:
http://www.opengroup.org/onlinepubs/007908799/xsh/fprintf.html

Bernd

Firmix Software GmbH                   http://www.firmix.at/
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          Embedded Linux Development and Services

Adrian Reber <[email protected]> writes:

|> When using the snprintf function from the kernel the length returned is
|> not the length written:
|> 
|> len = snprintf(test,1,"BLA 1"); 
|> 
|> len is 5 although test is "B"

Exactly how it should be.

|> the patch below fixes the symptom, but I am not sure if this is the real |> solution for this problem.

There is no problem here.

Andreas.

Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg
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"And now for something completely different."