Re: memset as memzero

Willy Tarreau
2007-09-23T18:59:29Z

On Sun, Sep 23, 2007 at 10:05:05AM -0700, Linus Torvalds wrote:
>
>
> On Sun, 23 Sep 2007, Arnaldo Carvalho de Melo wrote:
> >
> > bzero! That is it, its nothing new, just a sane name to something [..]
>
> No, please no!
>
> The BSD memory functions are nasty. If you do bzero, you logically should
> do the others too, and they are way inferior to the standard ones. Let's
> not go there.
>
> Besides, if we want to avoid mistakes, I would suggest going to a much
> higher level. Ie more along the lines of also fixing the size and
> alignment, and using something like
>
> #define memclear(p) memset(p, 0, sizeof(*(p)))

I don't like it when macros magically do sizeof(*p), because people often
think that the macro is smarter than it really is, and you commonly end
up with code looking like this :

char *p;
...
p = kmalloc(n);
...
memclear(p);

This can happen for instance when replacing a stack-allocated buffer
with a malloc because it became too big for the stack. Such a mistake
is *very hard* to detect by human eye, while having "sizeof(*p)" in
the same function as "char *p" will trigger some automatisms in most
readers' brains.

> because if you actually do something like
>
> git grep 'memset.*,[ ]*0[ ]*,'
>
> (those [..] things contatain a space and a tab), you'll see that a *lot*
> of them share that pattern.

At least current code is still greppable for such usages. Doing too
much magics with macros often harms debugging. I could agree with
having a macro to force the pattern to '0', but not to force the size.

> Not that I think it's really worth it.

I don't think either.

Willy