linux-kernel - Re: [PATCH 3/7] drivers: usb: Include appropriate header file in hcd.h

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Message-ID: <52B33180.60701@cogentembedded.com>
Date:	Thu, 19 Dec 2013 20:48:48 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Rashika Kheria <rashika.kheria@...il.com>,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, josh@...htriplett.org
Subject: Re: [PATCH 3/7] drivers: usb: Include appropriate header file in
 hcd.h

Hello.

On 12/19/2013 07:38 PM, Alan Stern wrote:

>>>> Include header file include/linux/usb.h in include/linux/usb/hcd.h
>>>> because structures usb_device, usb_host_config and usb_interface have
>>>> their definitions in include/linux/usb.h.

>>>> This eliminates the following warning in include/linux/usb/hcd.h:
>>>> include/linux/usb/hcd.h:311:44: warning: ‘struct usb_device’ declared inside parameter list [enabled by default]
>>>> include/linux/usb/hcd.h:412:10: warning: ‘struct usb_host_config’ declared inside parameter list [enabled by default]
>>>> include/linux/usb/hcd.h:614:9: warning: ‘struct usb_interface’ declared inside parameter list [enabled by default]

>>      Rashika, would it be enough to forward-declare these structures ISO
>> #include'ing the whole header?

> I agree, that would fix the problem.

    It should also make Greg happier. :-)

>>> Where does this problem show up?

>>> Any file that include linux/usb/hcd.h should include linux/usb.h first.
>>> IMO it would be better to fix the source files that don't do the
>>> includes properly.

>>      Yeah, let's fix the consequency instead of the cause. :-)

> The _real_ cause is that the Linux source code is extremely
> complicated, and it is remarkably difficult to insure that all header
> files have no unsatisfied dependencies.  How do you suggest fixing
> _that_?

> For example, suppose A.c includes B.h, and B.h includes C.h, and C.h
> defines struct foo.  Then A.c can use struct foo freely without
> including C.h directly (and this sort of thing happens quite a lot in
> the kernel source).  But consider what happens when B.h is changed so
> that it no longer includes C.h.

    That's a whole different issue than what we're dealing with.

>>> Of course, people have varying opinions on this issue.  As far as I
>>> know, there is no fixed policy in the kernel about nested includes.

>>      So far, I've only encountered the dubious policy of satisfying header's
>> dependencies in the files that include them is the USB tree.

> Have you looked in any other places?

    I have over 500 patches in the different areas of the kernel, so 
apparently I have if I'm telling you this. The only place where my patch to 
fix a header file so that it would be self-contained has encountered a 
maintainer's resistance was linux-usb. And note that it wasn't merely a case 
like this, where incomplete structure declarations would be enough, it was the 
case where the full structure declarations were needed.

> For that matter, how do you know
> that the USB tree has such a policy?

    From Greg KH. Also, from the late David Brownell.

>  Is it documented anywhere?

    I don't think so.

> Alan Stern

WBR, Sergei

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