Re: [PATCH] util: fix to get configuration macros in util/mmap-alloc.c

[Liu, Jingqi]

On 3/9/2020 9:35 PM, Peter Maydell wrote:
> On Mon, 9 Mar 2020 at 13:23, Liu, Jingqi <address@hidden> wrote:
> > On 3/6/2020 12:40 AM, Peter Maydell wrote:
> > > On Thu, 5 Mar 2020 at 16:11, Ján Tomko <address@hidden> wrote:
> > > > On a Thursday in 2020, Jingqi Liu wrote:
> > > > > The CONFIG_LINUX symbol is always not defined in this file.
> > > > > This fixes that "config-host.h" header file is not included
> > > > > for getting macros.
> > > > >
> > > > > Signed-off-by: Jingqi Liu <address@hidden>
> > > > > ---
> > > > > util/mmap-alloc.c | 2 ++
> > > > > 1 file changed, 2 insertions(+)
> > > > >
> > > > > diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> > > > > index 27dcccd8ec..24c0e380f3 100644
> > > > > --- a/util/mmap-alloc.c
> > > > > +++ b/util/mmap-alloc.c
> > > > > @@ -10,6 +10,8 @@
> > > > >    * later.  See the COPYING file in the top-level directory.
> > > > >    */
> > > > >
> > > > > +#include "config-host.h"
> > > > > +
> > > > According to CODING_STYLE.rst, qemu/osdep.h is the header file
> > > > that should be included first, before all the other includes.
> > > >
> > > > So the minimal fix would be moving qemu/osdep.h up here.
> > > Yes, osdep must always be first.
> > >
> > > > > #ifdef CONFIG_LINUX
> > > > > #include <linux/mman.h>
> > > > > #else  /* !CONFIG_LINUX */
> > > Do we really need this? osdep.h will pull in sys/mman.h
> > > for you, which should define the MAP_* constants.
> > >
> > > Also, you have no fallbmack for "I'm on Linux but the
> > > system headers don't define MAP_SHARED_VALIDATE or
> > > MAP_SYNC". Wouldn't it be better to just have
> > > #ifndef MAP_SYNC
> > > #define MAP_SYNC 0
> > > #endif
> > >
> > > etc ?
> > osdep.h pulls in sys/mman.h, which defines the MAP_* constants
> >
> > except for MAP_SYNC and MAP_SHARED_VALIDATE on Linux.
> Why not? Is this just "not yet in the version of glibc
> we're using", or is it a bug/missed feature in glibc
> that needs to be addressed there ?

I'm using the version 2.27 of glibc.

I downloaded the version 2.28 of glibc source for compilation and 
installation.

I found MAP_SYNC and MAP_SHARED_VALIDATE are defined in this version.

Seems it's older glibc version issue.

> > How about just adding the following code in util/mmap-alloc.c ?
> > #ifndef MAP_SYNC
> > #define MAP_SYNC 0x80000
> > #endif
> >
> > #ifndef MAP_SHARED_VALIDATE
> > #define MAP_SHARED_VALIDATE 0x03
> > #endif
> You don't want to do that for non-Linux systems, so there
> you need to fall back to defining them to be 0.
>
> Are there any systems (distros) where the standard system
> sys/mman.h does not define these new MAP_* constants but we
> still really really need to use them? If not, then we
> could just have the fallback-to-0 fallback everywhere.

Good point.

So as you mentioned, it would be better to just have the following code:

#ifndef MAP_SYNC
#define MAP_SYNC 0
#endif

#ifndef MAP_SHARED_VALIDATE
#define MAP_SHARED_VALIDATE 0
#endif

Thanks,

Jingqi

> thanks
> -- PMM