Re: conf: flush stdout before early exit

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 4 Jun 2025 17:00:36 +0200
Stefano Brivio <sbrivio@redhat.com> wrote:

> On Thu, 29 May 2025 13:08:58 -0400
> Jon Maloy <jmaloy@redhat.com> wrote:
> 
> > Before doing an early exit any contents of stdout is normally flushed.
> > This doesn't happen when the output goes into a pipe and we return with
> > _exit(). We now add an explicit flush in such cases.
> > 
> > Fixes: d0006fa784a7 ("treewide: use _exit() over exit()")
> > 
> > Signed-off-by: Jon Maloy <jmaloy@redhat.com>
> > ---
> >  conf.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/conf.c b/conf.c
> > index a6d7e22..a1d55a3 100644
> > --- a/conf.c
> > +++ b/conf.c
> > @@ -975,6 +975,7 @@ static void usage(const char *name, FILE *f, int status)
> >  		"    SPEC is as described for TCP above\n"
> >  		"    default: none\n");
> >  
> > +	fflush(f);
> >  	_exit(status);
> >  
> >  pasta_opts:
> > @@ -1029,6 +1030,7 @@ pasta_opts:
> >  		"  --ns-mac-addr ADDR	Set MAC address on tap interface\n"
> >  		"  --no-splice		Disable inbound socket splicing\n");
> >  
> > +	fflush(f);
> >  	_exit(status);
> >  }
> >  
> > @@ -1594,6 +1596,7 @@ void conf(struct ctx *c, int argc, char **argv)
> >  			FPRINTF(stdout,
> >  				c->mode == MODE_PASTA ? "pasta " : "passt ");
> >  			FPRINTF(stdout, VERSION_BLOB);
> > +			fflush(stdout);  
> 
> I was about to apply this, but clang-tidy now complains:
> 
> /home/sbrivio/passt/conf.c:978:2: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
>   978 |         fflush(f);
>       |         ^~~~~~~~~
> /home/sbrivio/passt/conf.c:978:2: note: cast the expression to void to silence this warning
> /home/sbrivio/passt/conf.c:1033:2: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
>  1033 |         fflush(f);
>       |         ^~~~~~~~~
> /home/sbrivio/passt/conf.c:1033:2: note: cast the expression to void to silence this warning
> /home/sbrivio/passt/conf.c:1599:4: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
>  1599 |                         fflush(stdout);
>       |                         ^~~~~~~~~~~~~~
> /home/sbrivio/passt/conf.c:1599:4: note: cast the expression to void to silence this warning
> 
> I don't see any sensible way to use the return value from fflush(),
> because, of course, if 'f' or stdout is not a valid stream or isn't open
> for writing (that's the only defined error for fflush()), it doesn't
> make sense to even try and print a warning to stdout or stderr.
> 
> So I would rather suppress the warning as suggested by clang-tidy
> (casting to void instead of a specific clang-tidy suppression, just in
> case other static checkers start complaining as well). I can do this on
> merge if you're fine with it.

I took that as a yes and went ahead with it, thanks for the fix!

-- 
Stefano