Re: [Ksummit-discuss] [MAINTAINERS SUMMIT] API replacement/deprecation

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Ted,

On Fri, Sep 7, 2018 at 10:56 PM Theodore Y. Ts'o <tytso@mit.edu> wrote:
> On Fri, Sep 07, 2018 at 10:30:04PM +0200, Arnd Bergmann wrote:
> > I suspect that a lot of the cases that want NUL-padding also don't
> > want NUL-termination: when you store a string on disk in a fixed-length
> > record or transfer it over the network, you don't want to leak stack
> > data to the medium, but you also don't need the terminating character
> > because you know the maximum length already.
> >
> > strncpy() does exactly the right thing for that case, it's just that
> > this pattern is now a corner case, and gcc tends to flag such
> > usage with a warning about missing termination (unless you
> > use __nonstring) but doesn't flag the more common usage when
> > it looks correct.
>
> Yeah, the case I have is when I'm copying from a NUL-terminated string
> into a fixed char array.  So if we had a function called
> "copy_string_to_char_array" (we'll figure out a better name later)
> which takes a source, destination, and size parameter, and which does
> the functional equivalent of:
>
>         memset(dest, 0, size);

Why the memset()? strncpy() pads the destination with zeroes, so it
is not needed. This is basically the major reason to use strncpy().

>         strncpy(src, dest, size);

Oh, you're copying in the wrong direction ;-)

> ... we could do something that's more efficient than the above, and
> does exactly what I'm looking for in this case.
>
> Of course, there could be other corner cases where strncpy() is
> justified; this is just the use case I care about.  :-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds