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

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	Dmitry Fleytman <dmitry.fleytman@gmail.com>,
	sheepdog@lists.wpkg.org,
	Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>,
	Li Zhijian <lizhijian@cn.fujitsu.com>,
	David Hildenbrand <david@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>,
	qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>,
	BALATON Zoltan <balaton@eik.bme.hu>,
	Keith Busch <keith.busch@intel.com>,
	Max Filippov <jcmvbkbc@gmail.com>,
	Gerd Hoffmann <kraxel@redhat.com>,
	"Edgar E. Iglesias" <edgar.iglesias@gmail.com>,
	Max Reitz <mreitz@redhat.com>, Yongbok Kim <yongbok.kim@mips.com>,
	Hannes Reinecke <hare@suse.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	zhanghailiang <zhang.zhanghailiang@huawei.com>,
	Ben Warren <ben@skyportsystems.com>,
	Stefan Berger <stefanb@linux.vnet.ibm.com>,
	Ronnie Sahlberg <ronniesahlberg@gmail.com>,
Subject: Re: [Qemu-block] [PATCH] qemu: include generated files with <> and not ""
Date: Tue, 20 Mar 2018 15:30:15 +0200	[thread overview]
Message-ID: <20180320152446-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20180320131041.GB24329@stefanha-x1.localdomain>

On Tue, Mar 20, 2018 at 01:10:41PM +0000, Stefan Hajnoczi wrote:
> 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.
> 
> Stale header files are a pain.  I often do make distclean before
> checking out a radically different QEMU version to avoid the problem.
> 
> This patch trades off the stale header file issue for a new approach to
> using <> vs "", which will be hard to use consistently

The proposed rule is to use <> everywhere except if the file is in the
source directory.  It will be very easy to use consistently for the
simple reason that compiler will enforce it.  If you use <> for a header
in the current directory build fails. So you are forced to use "".

> in the future
> since it is unconventional.

All compilers I know without exception implement
include <> meaning look in -I search path, and
include "" meaning look in current directory then
in -I search path.

Looks conventional to me.

> Is the build time improvement worth it (please post numbers)?
> 
> Stefan

Haven't tested it frankly. Will it convince anyone if it's marginally
faster?

-- 
MST

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel