linux-kernel - Re: [PATCH v1] firmware loader: introduce module parameter to customize fw search path

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Message-ID: <CA+55aFzoJULimHhYHdb-BW1bqSAY8FUevPnYu-K6nDa7xRtg2w@mail.gmail.com>
Date:	Thu, 25 Oct 2012 20:38:25 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] firmware loader: introduce module parameter to
 customize fw search path

On Thu, Oct 25, 2012 at 8:12 PM, Ming Lei <ming.lei@...onical.com> wrote:
>
> Yes, it should be the cleanest, I don't do it because I thought that might
> have caused one compile warning('const char *' points to memory
> without 'const', like below)

You can just keep the const.

In fact, you could even add one, and make it be

   static const char * const fw_path[] = {

We currently don't mark fw_path[] itself const (even though it is),
only the strings it points to.

> but in fact there isn't any warning with above change and it does work, still
> don't know why? :-(

It's valid to cast a non-const pointer to a const one. It's the
*other* way around that is invalid.

So marking fw_path[] as having 'const char *' elements just means that
we won't be changing those elements through the fw_path[] array
(correct: we only read them). The fact that one of those same pointers
is then also available through a non-const pointer variable means that
they can change through *that* pointer, but that doesn't change the
fact that fw_path[] itself contains const pointers.

Remember: in C, a "const pointer" does *not* mean that the thing it
points to cannot change. It only means that it cannot change through
*that* pointer.

           Linus
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