Re: [Qemu-devel] [PATCH 0/8] Clean up #include "..." vs "<...>" and header guards

[Daniel P . Berrangé]

On Wed, Mar 20, 2019 at 01:52:26PM +0000, Stefan Hajnoczi wrote:
> On Fri, Mar 15, 2019 at 03:51:15PM +0100, Markus Armbruster wrote:
> > * Our use of header guards is rather sloppy.  Sloppiness there can
> >   lead to confusing compilation errors.  The rest of the series cleans
> >   up existing header guards.  In particular, it normalizes guard
> >   symbols to follow a common pattern, in the hope of making clashes
> >   less likely.  It doesn't add new header guards.  We have more than
> >   200 headers without a recognizable header guard.  A few of them are
> >   for multiple inclusion, a few more don't need header guards because
> >   they don't do anything but include, but the majority probably should
> >   have one.  Left for another day.
> 
> Time for #pragma once?
> https://en.wikipedia.org/wiki/Pragma_once

That seems like a reasonable idea to me. We already mandate CLang or
GCC as only supported compilers, so there's no portability concerns.


On the subject of non-standard C extensions, I was also wondering if
QEMU should consider use of __attribute__((cleanup($func))) for doing
automatically free'ing of memory when variables go out of scope. As
well as reducing possibility of memory leaks, this simplifies code
as it often allows for many "goto cleanup" jumps to be replaced with
direct "return -1"s.  It isn't the most attractive syntax, but that
downside doesn't outweigh the positives from my POV.

We recently started using it in libvirt for this reason.

Glib2 itself already uses this since 2.44 and exposes some macros for
client code to use for this.

We bumped min glib to 2.40 a year go because Debian Jessie has 2.42
and Ubuntu Trusty needs 2.40 which Peter used as a build merge test
machine.

Our platform support policy will let us drop Jessie support when
Buster is released fairly soon. If Peter no longer uses Trusty
machines for buld, we'll soon be able to have a min glib that uses
attribute(cleanup) as a standard dep.

Regards,
Daniel
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