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
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