On Thu, Oct 16, 2014 at 10:55:57AM -0700, Joe Perches wrote:
> On Thu, 2014-10-16 at 13:48 -0400, Jason Cooper wrote:
> > On Thu, Oct 16, 2014 at 10:25:03AM -0700, Joe Perches wrote:
> > > On Thu, 2014-10-16 at 19:15 +0200, Rickard Strandqvist wrote:
> > > > The buf is used to hold the list of hwrng devices registered.
> > > > The old code ensures we don't walk off the end of buf as we
> > > > fill it, but it's unnecessarily complicated and thus difficult
> > > > to maintain. Simplify it by using strlcat.
> > > > We also ensure the string within buf is NULL terminated
> > > > so the final strlen is ok.
> > > []
> > > > diff --git a/drivers/char/hw_random/core.c
> > > > b/drivers/char/hw_random/core.c
> > > []
> > > > @@ -289,16 +288,13 @@ static ssize_t hwrng_attr_available_show(struct
> > > > device *dev,
> > > > return -ERESTARTSYS;
> > > > buf[0] = '\0';
> > > > list_for_each_entry(rng, &rng_list, list) {
> > > > - strncat(buf, rng->name, PAGE_SIZE - ret - 1);
> > > > - ret += strlen(rng->name);
> > > > - strncat(buf, " ", PAGE_SIZE - ret - 1);
> > > > - ret++;
> > > > + strlcat(buf, rng->name, PAGE_SIZE);
> > > > + strlcat(buf, " ", PAGE_SIZE);
> > > > }
> > > > - strncat(buf, "\n", PAGE_SIZE - ret - 1);
> > > > - ret++;
> > > > + strlcat(buf, "\n", PAGE_SIZE);
> > > > mutex_unlock(&rng_mutex);
> > > >
> > > > - return ret;
> > > > + return strlen(buf);
> > > > }
> > > >
> > > > static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
> > >
> > > Rickard, can you please use some optimizations here
> > > (and elsewhere) so that strlcat doesn't always have
> > > to strlen the first string and the return doesn't
> > > have to do the strlen too?
> >
> > Joe, is further optimization worth the effort? This function is only
> > called when the end user reads the sysfs file rng_available...
>
> It's unlikely that it matters much here.
>
> I just don't like the repeated and unnecessary strlen.
>
> I do imagine this pattern being repeated though where
> it does matter.
Agreed. Back to why I like to see descriptions from the author
demonstrating they grok the code they are changing :)
thx,
Jason.
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