Re: [Xen-devel] [PATCH v2] qemu: replace "" with <> in headers

[Daniel P. Berrangé <berrange@xxxxxxxxxx>]

On Wed, Mar 21, 2018 at 05:39:48PM +0200, Michael S. Tsirkin wrote:
> On Wed, Mar 21, 2018 at 03:19:22PM +0000, Daniel P. Berrangé wrote:
> > On Wed, Mar 21, 2018 at 04:46:32PM +0200, Michael S. Tsirkin wrote:
> > > Our current scheme is to use
> > >  #include ""
> > > for internal headers, and
> > >  #include <>
> > > for external ones.
> > > 
> > > Unfortunately this is not based on compiler support: from C point of
> > > view, the "" form merely looks up headers in the current directory
> > > and then falls back on <> directories.
> > > 
> > > Thus, for example, a system header trace.h - should it be present - will
> > > conflict with our local trace.h
> > 
> > If our local "trace.h" is in the current directory, then using ""
> > is right and you can still use <trace.h> to get the system version.
> > 
> > If our local trace.h is in include/ top level, then it is going to
> > block use of the system trace.h regardless of whether we use <> or ""
> > 
> > Fortunately our include/ tree uses sub-dirs, so we would typically
> > use  #include "$subdir/trace.h" and  #include <trace.h> would still
> > find the system header.
> > We just have to be careful we don't add stuff at the top level of
> > our include/ dir with names that are liable to clash. This might
> > suggest renaming  include/elf.h to include/qemu/elf.h, or just
> > moving elf.h to the qemu/ subdirectory. Likewise include/glib-compat.h
> > might be better moved to qemu/ subdirectory.
> > 
> 
> This is exactly what this patch proposes, with a uniform scheme:
> start everything with qemu/.
> 
> > 
> > > As another example of problems, a header by the same name in the source
> > > directory will always be picked up first - before any headers in
> > > the include directory.
> > 
> > There's only a couple of headers in the top level of our include/
> > directory - everything else is pulled in with a named path
> > eg #include "block/block_int.h", so that would not conflict with
> > reference to a bare #include "block_int.h" from the current directory.
> 
> We can not know that there are no system headers that start with block/ on
> any current or future systems.

Ah true, good point.  I guess that's where the benefit of -iquote
comes into play.


Regards,
Daniel
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