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

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

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

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