Re: [PATCH rdma-core 2/5] util: Fix check_snprintf to use __rc__ for local

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Fri, Sep 01, 2017 at 07:56:32AM +0300, Leon Romanovsky wrote:
> On Thu, Aug 31, 2017 at 02:50:56PM -0600, Jason Gunthorpe wrote:
> > To avoid clashing with user variables.
> >
> > Signed-off-by: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
> >  util/util.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/util/util.h b/util/util.h
> > index cbf0deca2dde7b..30d32ee6b51e24 100644
> > +++ b/util/util.h
> > @@ -8,8 +8,8 @@
> >   * error */
> >  #define check_snprintf(buf, len, fmt, ...)                                     \
> >  	({                                                                     \
> > -		int rc = snprintf(buf, len, fmt, ##__VA_ARGS__);               \
> > -		(rc < len && rc >= 0);                                         \
> > +		int __rc__ = snprintf(buf, len, fmt, ##__VA_ARGS__);           \
> 
> It can't clash, because it is declared in the scope {..} of that define and
> it is local to check_snprintf macro.

This triggers a -Wshadow warning:

 int rc;
 check_snprinf(str, sizeof(str), ..)

And rc is commonly used in callers, so it shouldn't.

Perhaps this addresses all the concerns:

/* Return true if the snprintf succeeded, false if there was truncation or
 * error */
static inline bool __good_snprintf(size_t len, int rc)
{
	return (rc < len && rc >= 0);
}

#define check_snprintf(buf, len, fmt, ...)    \
	__good_snprintf(len, snprintf(buf, len, fmt, ##__VA_ARGS__))

Jason
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