Re: [PATCH] ALSA: Warn when control names are truncated

[Takashi Iwai <tiwai@suse.de>]

At Wed, 29 Oct 2008 19:31:25 +0100 (CET),
Jaroslav Kysela wrote:
> 
> On Wed, 29 Oct 2008, Takashi Iwai wrote:
> 
> > At Wed, 29 Oct 2008 15:51:40 +0100 (CET),
> > Jaroslav Kysela wrote:
> > > 
> > > On Wed, 29 Oct 2008, Takashi Iwai wrote:
> > > 
> > > > At Wed, 29 Oct 2008 14:40:30 +0000,
> > > > Mark Brown wrote:
> > > > > 
> > > > > This is likely to confuse user interfaces since the end of the control
> > > > > name is interpreted (eg, "Volume", "Switch").
> > > > > 
> > > > > Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
> > > > 
> > > > Thanks, applied now.
> > > > 
> > > > 
> > > > > +		if (strcmp(ncontrol->name, kctl.id.name) != 0)
> > > 
> > > Maybe better is to just use end char comparsion to save few CPU ticks:
> > > 
> > > if (kctl.id.name[sizeof(kctl.id.name)-2] != '\0' &&
> > >     ncontrol->name[sizeof(kctl.id.name)-1] != '\0')
> > 
> > No, this may cause segfault
> 
> How? The first check in the fixed size variable initialized with zeros 
> allocated on heap ensures that ncontrol->name string is at least 
> sizeof(kctl.id.name) long. There is no possibility of segfault.

Hm, OK, this would work indeed surprisingly.

> 
> > (and way too hacky to understand what's the purpose of the code...)
> 
> The printk explains check nicely.

Uh, no.  The problem is that you'll likely need to consider what
really the code does and even whether it's correct at the first
glance.  That's definitely bad for readability.

Since the code path is absolutely no fast path and a rarely used
path, there is no win at all in practice for such a nano
optimization.


Takashi