Re: [PATCH] qemu: include generated files with <> and not ""

From: "Michael S. Tsirkin" <mst@redhat.com>
To: qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>,
	Dmitry Fleytman <dmitry.fleytman@gmail.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Li Zhijian <lizhijian@cn.fujitsu.com>,
	David Hildenbrand <david@redhat.com>,
	Jeff Cody <jcody@redhat.com>, Zhang Chen <zhangckid@gmail.com>,
	Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>,
	BALATON Zoltan <balaton@eik.bme.hu>,
	Keith Busch <keith.busch@intel.com>,
	Max Filippov <jcmvbkbc@gmail.com>,
	Laurent Vivier <laurent@vivier.eu>,
	Gerd Hoffmann <kraxel@redhat.com>,
	"Edgar E. Iglesias" <edgar.iglesias@gmail.com>,
	Jiri Pirko <jiri@resnulli.us>,
	Subbaraya Sundeep <sundeep.lkml@gmail.com>,
	Eric Blake <eblake@redhat.com>,
	Michael Roth <mdroth@linux.vnet.ibm.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Josh Durgin <jdurgin@redhat.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Alberto Garcia <berto@igalia.com>,
	zhanghailiang <zhang.zhanghailiang@
Subject: Re: [PATCH] qemu: include generated files with <> and not ""
Date: Tue, 20 Mar 2018 15:05:00 +0200	[thread overview]
Message-ID: <20180320145402-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <1521510562-529051-1-git-send-email-mst@redhat.com>

On Tue, Mar 20, 2018 at 03:54:36AM +0200, Michael S. Tsirkin wrote:
> QEMU coding style at the moment asks for all non-system
> include files to be used with #include "foo.h".
> However this rule actually does not make sense and
> creates issues for when the included file is generated.
> 
> In C, include "file" means look in current directory,
> then on include search path. Current directory here
> means the source file directory.
> By comparison include <file> means look on include search path.
> 
> As generated files are not in the search directory (unless the build
> directory happens to match the source directory), it does not make sense
> to include them with "" - doing so is merely more work for preprocessor
> and a source or errors if a stale file happens to exist in the source
> directory.
> 
> This changes include directives for all generated files, across the
> tree. The idea is to avoid sending a huge amount of email.  But when
> merging, the changes will be split with one commit per file, e.g. for
> ease of bisect in case of build failures, and to ease merging.
> 
> Note that should some generated files be missed by this tree-wide
> refactoring, it isn't a big deal - this merely maintains the status quo,
> and this can be addressed by a separate patch on top.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

For the record, the stated advantage is that one can
have a header file that happens to match the system
header.

To put it bluntly that does not work as designed.

For example, if a system header foo.h somewhere has #include <trace.h>
then the compiler will happily pull in our own version (since that is in
the -I path) and completely ignore the system one, breaking things in
the process.

When does it make sense to use include ""? When the header is
a directory-specific one, located with the source.
This approach would both be enforced by the compiler
and help people know where to find the header.

-- 
MST

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