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

[Lennart Poettering]

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...

Lennart

-- 
Lennart Poettering - Red Hat, Inc.