[systemd-devel] [RFC/PATCH] Use initalization instead of explicit zeroing

[Zbigniew Jędrzejewski-Szmek]

On Fri, Apr 05, 2013 at 03:51:47PM -0300, Lucas De Marchi wrote:
> On Fri, Apr 5, 2013 at 2:50 PM, Lennart Poettering
> <lennart at poettering.net> wrote:
> > On Sun, 31.03.13 15:57, Zbigniew Jędrzejewski-Szmek (zbyszek at in.waw.pl) wrote:
> >
> >> Hi everyone,
> >> I'm pretty sure this a good step, but just in case, I'm posting
> >> here for review (more of the general idea, not the specifics,
> >> because the patch is pretty well checked by the compiler...).
> >>
> >> Zbyszek
> >>
> >> ---- patch ----
> >>
> >> Before, we would initialize many fields twice: first
> >> by filling the structure with zeros, and then a second
> >> time with the real values. We can let the compiler do
> >> the job for us, avoiding one copy.
> >
> > Hmm, I assumed the compiler would handle memset on its own anyway these
> > days, at least if you specifiy -O2 or so... Did you try with
> > optimization on?
> >
> >>          else {
> >> -                struct sched_param p;
> >> +                struct sched_param p = {};
> >>
> >> -                zero(p);
> >
> > I would have assumed that particularly in cases like this the compiler
> > would generate the exact same code... Mayb I am overestimating gcc's
> > handling of memset however...
> >
> > One could argue that zeroing out the struct in this particular case is
> > totally unnecessary anyway, and we could just get rid of it entirely...
> >
> >>                  if (sched_getparam(0, &p) >= 0)
> >>                          n = p.sched_priority;
> >> -        union sockaddr_union sa;
> >> +        union sockaddr_union sa = {
> >> +                .un.sun_family = AF_UNIX,
> >> +                .un.sun_path = "/run/systemd/journal/stdout",
> >> +        };
> >
> > For cases like this, this definitely appears worthwile! (It makes things
> > more readable even...)
> >
> >>          struct sock_filter *f;
> >> -        struct sock_fprog prog;
> >> +        struct sock_fprog prog = {};
> >
> > I wonder if we should have a macro for this... {} looks so ugly... or
> > maybe not...
> 
> it doesn't when you get used to it ;-)
Yeah, I think that it's not bad. Also it's simple enough to be hard to get
wrong :)

Zbyszek